Introduction to Ecology
Introduction to Ecology EVE 101
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EVEl 01 Lecture 10 Part I Page 1 Lecture 10 outline Community Ecology Part I Part I I Introduction 39 A Overview 39 B Goal for the remainder of the course II Biodiversity 39 A Spatial patterns local regional and global diversity 39 1 Definitions based on spatial scale 39 2 Determinants of latitudinal gradients in a and diversity Part II 39 B Temporal patterns Succession 39 C Spatial and temporal patterns Island biogeography and species turnover 39 D Stability and complexity in food webs III Applications 39 A World Biomes revisited 39 B Conservation planning revised March 3 2008 Molles 4 edition pages Lecture 10 Community Ecology Part I Readings Molles Chapters 16 17 20 21 22 for all parts of Lecture 10 I Introduction A Overview In the lecture on competition we gradually widened our View from two to many species at a time Focusing on just two species at a time is often a good way to understand what happens with many species Quite a few patterns can be understood by adding the subpatterns together There are other patterns however which can only be viewed and understood by looking at many species at a time This is the realm of quotcommunity ecologyquot Community ecology examines patterns only visible by considering many species at a time We have already examined some community parts by focusing on parts of communities for example many competitors one type of population interaction on 1 trophic level Now we will focus on all of the species that occur at one location including all trophic levels and all types of possible interactions For example community ecology can examine the relationships between different types of two species interactions in food web what happens when competitors are preyed upon Or how many interactions do we expect to see in a food web with a certain number of species Will all species be interacting Will some kinds of interactions be more 2008 Catherine A Toft EVE101 Lecture 10 Part I Page 2 common than others And so on Here is a list of patterns and topics that can only be understood and defined taking many species at a time Molles Ch 160 161 162 39 1 species diversity We can count the number and relative abundance of species and try to explain what determines these patterns worldwide We now call this BIODIVERSITY 39 2 community structure a general term for properties of food webs such as a Complexity This component of community structure refers to the numbers and types of species in the community and the numbers and types of interactions connections links between each pair of species These properties can be descriptors of the complexity of food webs and communities 39 number of trophic levels length of food chain 39 number of species on each trophic level and their similarity 39 numbers of interactions including of species in the food web that interact with 1 2 3 n species connectance ratio of different types of interactions etc b Stability This component of community structure refers to the dynamical properties of the community in other words the behavior of interacting populations refer to Lecture 6 if you need to remind yourself of our definition of population behavior These properties are components of the stability of food webs and communities 39 time to return to equilibrium resilience 39 resistance to disturbance 39 probability of extinction of any of the component populations 39 3 succession and community development regular or predictable changes in communities with time We can view this as predictable responses of communities to disturbance 39 4 speciesarea relationships island biogeography how number of species changes with increasing area This topic also emphasizes the turnover of species in time 39 5 ecosystem and landscape ecology study of the community and all the physical forces impinging on it at one site including energy and nutrient ow and the links between different ecosystems occupying a landscape In this course we will skip study of ecosystems It is impossible to cover the field of ecology in only 10 weeks Rather than give you a superficial understanding of everything I have tried to go into depth in a coherent set of subdisciplines of ecology 2008 Catherine A Toft EVEl 01 Lecture 10 Part I Page 3 B Goal of the rest of the course We will wrap up the course by considering community level patterns First let s take a moment to re ect on what we have covered so far so that we can use this section to pull many concepts together What we have emphasized in this course is evolutionary ecology and population based ecology Those two viewpoints are highly related as the deme is the setting for natural selection To unify the course the theme of this last unit is will be the topic of biological diversity We want to ask quotWhat determines the number of species found in one locationquot which is a rephrasing of how we defined the subject of ecology at the beginning of the class quotWhat determines the distribution and abundance of organismsquot We can also call this quotbiodiversityquot or quotspecies diversityquot Conservation Biology is a new field of study which is developing as an applied area that combines ecology and population genetics Many students want to pursue this new field because of their desire to help stem the growing quotbiodiversity crisisquot In other words the activities of humans are causing the extinction of other species on a scale not seen since the giant bolide collided with the Earth 65 million years ago Any viable applied field and its practitioners require a solid founding in the principles of the basic sciences most closely allied to this applied field For the rest of the course we will investigate the ecological determinants of biodiversity as a function of spatial and temporal variation We have gotten many of the building blocks of to address the question of biodiversity already In this section we will cover some more concepts and tie things together 11 What determines biological species diversity Because this is an ecology course we will primarily emphasize the ecological aspects of biodiversity A Spatial patterns local regional and global diversity 1 Exactly What do we mean by biologicalspecies diversity We will restrict our view of biological diversity to mean species diversity and not genetic diversity Species diversity is Molles 162 39 1 the number of species species richness and 39 2 the relative abundance of those species at one time and one place species evenness 2008 Catherine A Toft EVEI 01 Lecture 10 Part I Page 4 There are 4 categories of species diversity that each depend on spatial scale 39 0 diversity alpha diversity is strictly species diversity within one habitat quotlocalquot 3 diversity beta diversity is species diversity in one place with more than one habitat type sum of OL diversity in a place that is spatially heterogeneous Y diversity gamma diversity is quotregionalquot species diversity 39 global diversity all of the species on the planet quot Spatial scalequot is somewhat arbitrary here what s one habitat and what s a region The best way to View these definitions is as working de nitions In local or alpha diversity we are considering populations in a location that is spatially fairly homogenous with population densities and interactions being pretty much the same in the entire are In betadiversity we are conceding that populations occur over spatial scales in which the environment varies and so do the other populations that a focal population can interact with In gammadiversity we are talking about something less well defined but in general we can think of it as a group of populations unified over a larger spatial scale by something ecologically important for example a common biogeographic history or a common biome type By definition a region is somehow spatially contiguous but arbitrarily large A region might be a watershed a mountain range an island archipelago a small continent or part of a large continent In community ecology especially we enter a realm of terms that are potentially quotbuzz wordsquot that is words for which the definition takes on a life of its own We will want to keep grounded solidly in our pursuit of understanding of ecological processes In defining words we want to focus on a set of ecologically interesting processes With this View we can define a level of species diversity according to What kinds of processes occur on each spatial scale that we want to understand Finally we can talk about global diversity or all of the species on the planet In both gamma diversity and global diversity there is a significant evolutionary component to the determinants of species diversity whereas only ecological factors are considered to determine local diversity alpha and beta diversity Thus regions are large enough that speciation has occurred in the region and can be considered a source of species diversity Indeed speciation is the original source of species diversity 2 What determines global and gamma diversity a mix of evolutionary and ecological processes 39 Global and gamma diversity could be determined by a macroevolutionary process for example global and y diversity speciation minus global extinction or the available quotpoolquot of species at any one time However these levels of diversity are NOT independent of all the local events and processes that determine oc diversity that is it depends very much on local events e g Molles Ch 222 quotDifferences in speciation 2008 Catherine A Toft EVEl 01 Lecture 10 Part I Page 5 and extinction ratesquot 39 Gamma diversity and global diversity also result from adding up many many local processes over the entire region or planet For the rest of this course we are going to focus on these local processes 3 What determines local 1 and diversity primarily ecological processes 39 invasion minus local extinction which gives you the total number of species in one location 39 But we also want to know what determines exact population sizes to understand what determines the relative abundance of species ie species diversity We need to look at the ecological processes at work that determine which invasions succeed and when species will persist or go extinct and finally what determines the size of any given population Summary Local diversity is the number of species weighted by population density relative abundance or evenness of densities of all species combined If you go on in ecology you will learn about a number of species diversity indices Obviously if a species is very rare in a local area it is more likely to go extinct Conversely a species can be so abundant that its impact dominate the characteristics of the community at that site So we have to consider not only presence absence of species but also the density of individuals representing that species 4 Patterns and determinants of local species diversity latitudinal gradients Molles Ch 223 We can deduce many of these from the latitudinal gradients in species diversity A conspicuous pattern is the change of species diversity with latitude eg Figs 2215 17 There is a gradient in which species diversity is highest in the tropics astounding numbers of species and species diversity gradually gets less as you go to higher latitudes and is lowest at the poles You can see the gradient even within segments of narrower ranges of latitudes such as lizards or breeding birds of North America or United States etc For example one hectare in Peru has over 600 breeding bird species nearly as many as in all of North America This incredible diversity applies also to insects many times over No one knows or will ever know the full diversity of arthropods in the tropics because of the tragedy of deforestation at these latitudes Whatever causes the latitudinal gradient of species diversity should give us a clue as to the determinants of species diversity at any given location We know the things that vary with latitude so we can start there Unfortunately this gives us a lot of non mutually exclusive competing hypotheses but that is the way ecology is Patterns at the community level are obviously determined by several to many interacting factors I have arranged the factors determining local diversity in order of building complexity starting with mechanisms that quotstand 2008 Catherine A Toft EVEl 01 Lecture 10 Part I Page 6 alonequot and going to mechanisms that depend on previous ones Molles Ch 223 12 Obviously the time scale is important Mechanisms ie how does this factor determine species diversity are 39 1 Evolutionary With enough time species can evolve in situ Some say that tropics have been undisturbed by extinctions and major environmental disasters eg as caused by ice ages for longest time But this is controversial the tropics were indeed affected strongly by the ice ages even though there were no glaciers there 2 Ecological have population dynamics had enough time to go to equilibrium ie will we see more extinctions or invasions in the future In the tropics where there are relatively fewer disturbances see below populations have had enough time to go to equilibrium whatever that is There are two types of situations to consider 39 If populations are vulnerable for example if they are small or if they have a strong Allee effect then such populations are less likely to go extinct where there are fewer disturbances These populations could contribute to higher species diversity in the tropics if we assume that there are fewer disturbances there If the outcome of a population interaction competition or predation in particular is extinction then disturbances can prevent this outcome For such populations species diversity will be higher where there is more disturbance see below 3 Climatic quotstabilityquot By climatic stability we generally mean the constancy and predictability of climate and weather which is higher on average in the tropics Changes in weather can disturb populations Also we think of quotbenignquot climates such as found in the tropical latitudes as being less disturbing to populations Mechanism 39 Presumably in areas with more constant and predictable climates there are fewer perturbations and fewer disturbances affecting populations meaning that populations are less likely to go locally extinct 39 Also specialists can be supported because of predictability of their narrower range of resources conversely if a population cannot count on a narrow or special array of resources individuals in the population should be more flexible in their use of resources food etc such individuals would be quotgeneralistsquot But the major climatic features of the tropics leads to other major factors 2008 Catherine A Toft EVE101 Lecture 10 Part I Page 7 4 Productivity We might combine this with the energy hypothesis There is higher productivity in the tropics in terms of fixing more energy by primary quotproducersquot plants because of higher solar input and higher humidity that favors greater rates of potential evapotranspiration which favors higher rates of photosynthesis Mechanism With more total resources more total individuals possible to be divided among more species rarer species then can be supported Also with more resources around specialization is favored for example in optimal foraging theory so this factor and 3 climatic constancy both favor specialists Your book page 517 8 lists apparent contradictions to this hypothesis but we need to keep in mind an all else equal perspective Remember that these hypotheses are NOT mutually exclusive and areas such as the tropical latitudes have more factors favoring higher diversity for example Higher productivity and climatic stability leads eventually to 5 quotHabitat complexityquot Plants are 39habitat39 for animals Thus factors that favor plants produce environmental complexity for animals This is where animal ecologists start features of the physical environment and plant community provide resources for animal populations Mechanism The more quotresourcesquot ie more resource quottypesquot as opposed to amounts be they food food species nest sites shelters from microclimate or predators ie from 1 absolute amount of a resource productivity AND 2 variety of resources the more populations and larger populations are able exist in a location The more resources available the higher the species diversity eg Molles Fig 169 Bird species diversity and foliage height diversity The more resources vary the more species can partition resources again favoring specialists and in particular avoid competitive exclusion 6 Spatial heterogeneity If the physical environment is more variable then we might except more species This is in part a companion to the above habitat complexity but it is more general Species are adapted to local physical environments but because there are more of them in a given area then there are more species in a given area This mechanism is actually the quot5 diversityquot we discussed above a somewhat larger spatial scale relative to the amount of spatial variability It is not clear whether the tropics should be greater in spatial heterogeneity compared to other latitudes The specific mechanisms could include the accumulation of species with differing ecophysiological adaptations and as above the ability to avoid interspecific competition 7 Competition p 518 under quotniche breadths and interspecific interactions see also ch 163 Competition as an interspecific interaction can cause extinction and lower fitness The ways in which it influences species diversity depends very much on the time scale 2008 Catherine A Toft EVEl 01 Lecture 10 Part I Page 8 Mechanism 39 A In evolutionary time competition can increase the number of species by favoring specialists through ecological character displacement ECD While competition does not result directly in speciation ECD can reduce extinction ie competitive exclusion And it is possible that specialization could favor speciation by predisposing populations to diverge in sympatry and thus differ from the same species somewhere else For example in the Darwin39s finches we saw populations of the same species evolving different bill sizes on different islands depending on what other species they shared a given island with Such differences might eventually lead to speciation 39 B In ecological time competition can decrease the number of species through competitive exclusion Competition puts an upper limit on the number of species that can live in one location If resources are limiting then species can competitively exclude other species The limit to similarity means that niches are quotincompressiblequot beyond a certain point So there is an upper limit to the number of competing species that can coexist on a given amount or variety of resources We have already discussed factors above that can interact with competition as mechanisms for determining species diversity For example in the tropics with benign climate high productivity and high habitat complexitiy specialists can be supported While competition may be intense especially high in food webs specialists can do well and so resource partitioning is favored and competitive exclusion is decreased 8 Predation Predation also can affect species diversity in two ways Mechanism 39 intense predation can lead to extinction of prey species We expect this type of extinction more in simple food webs and in settings were not much evolutionary and ecological time has gone by ie new predators on a particular prey Thus in some settings predation can decrease species diversity Because the tropics are more complex we might expect there to be fewer extinctions based on this mechanism 39 predation on top of competition can prevent competitive exclusion chs 164 172 intermediate disturbance hypothesis We saw how predators can hold prey below their carrying capacity When prey species are potential competitors which should happen relatively often a predator or set of predators will hold them all below their carrying capacities That is predators not interspecific competition regulates the prey populations recall how we defined quotregulationquot of prey by predators What does this mean for species diversity If competition leads to competitive exclusion when species are too similar then predators that keep species from competing permit more and more similar species to coexist 2008 Catherine A Toft EVE101 Lecture 10 Part I Page 9 Summary Predation on communities of potentially competing prey increases species diversity by reducing competition and reducing the incidence of competitive exclusion In the tropics predation is often intense also depending on the trophic level This principle has been termed the quotKEYSTONE PREDATORquot effect Keystone predators are seen most often in space limited communities which tend to have competitive hierarchies superior vs inferior competitors more do than food limited communities Food limited communities tend to avoid competition by resource partitioning ie constriction of the fundamental niche to the realized niche The term quotkeystonequot implies that a single species has particularly strong effects on all of the others Is there a keystone species in the kelp food web Examples include 39 Pisuster the predatory starfish eats a competitive hierarchy of species competing for space in the rocky intertidal The hierarchy from superior to inferior competitors goes like this mussels gt barnacle species 123 gt algae in the rocky intertidal The starfish prefers the mussels as prey so the starfish opens up space for the other less able competitors to occupy Molles Fig 177 9 Darwin s lawnmower generalist grazing herbivore Darwin noticed that when he mowed his lawn regularly he could find more species of plants in it Again we are talking about species competing for space Darwin didn39t follow up on his experiment so we don39t know if there was a competitive hierarchy but that is likely based on what is known of other pasture lands Grazing herbivores may be similar to a lawnmower but unlike a lawnmower some herbivores are specialists they are likely to select species rather than graze all species equally In some settings ie on grasslands that coevolved with grazing herbivores some studies show that grazing herbivores increase species diversity However in others species diversity decreases in the face of grazing Reasons for this contraction may include 1 these examples are humans grazing rangeland with domestic livestock which did not coevolve with plant species in those settings and 2 humans over grazing rangelands in which case a similar principle to below the quotintermediate disturbance hypothesisquot may apply extreme disturbance see below or extreme grazing pressure necessarily lowers species diversity by driving some species to extinction Molles Fig 1620 p 386 Fig 17 9 p 401 39 Herbivorous insects on trees leaf hoppers histidine beetles work of Professor Strong and others This is an example that does not involve competition for space The hypothesis is that so many species of insect species all of which depend on eating leaves of any given tree species can coexist Most astonishing is that one species of tree may have a large number of herbivorous insects that specialize on that species to the exclusion of all other species of trees There is little partitioning of resources within that 2008 Catherine A Toft Ewm bssmsm Pm pssm mmmumty Thus 1 mmpeuunn m xesaumes bs bssumbg haw these sps s Daexlst Wauld bs smyssxy Tbs absrbsuys and fawxed hypadnesls bs bbsubs papula ans bf bexhwumus bbssscs ale legulaied bypssbsbsbs mbsuy the speuahzed mssmbsxssmm T Tbsss bass are pan at the famaus hypadnesls bmbbsm mm m Shhudln39n 1155an ssbsb why bs the wand green bb bbs b sswsbbb that unis plan39s ale sssb up by berhwmes Tbs bass s that bbs deiermmant afspeues abysbsuy mthm a h ayhu level snsmscss between mph levels puns ale sbbbsusb by cumpe nn because I babisz ale sbbbsusb by prelisz sb that bbsss predsz ale sbbbbusb by mmpeti nn en a nismbsnbsbnmpmmpsmbn Inspmerhmmd mmmunmes disturbance 3239s bbss pxsdsm nssbbsbsuy bubsbbbmymbsss autafspabe and EIEI syane m bbbsnbmymsbs When absbubsbbs bs bbmssnmbbaas lbke Darwin s lawn bbs m emu bysx nusessanly bbbsbs animals b super sbmp s a s 1 sub 1 Me ssbbgsgmbsubs bk thbs bbstbsbbsmbsbbsb mwn e spansandm memediversityafsessxl speuesa anhnganmcksm miemd ms F135 15 Hz ms xbsbms sla b might s bbss bsmb sbbb Lbemechan mssbsb artbalecalagls39sa gndamidiscnmm s etwe disturbancecaused b ayrsdamxanddlsmxhanueca hyan bsbybbgmmbbpmbmmmwm ab cammunmes bmbbsb hyfaad psbsbbb might ms dl elenne bbsb bbbsbymg absubbsbsss Fue s sbbbbsmsm type bmsmbsbbs capable bfbmsbg speues bwsbsny bb sbsss bmbbsb cammumnes Tbs type brpbsbbmsbbb led m bbs pmpbssbbnbs INTERMEDIATE DISTURBANCE HYPOTHESIS F1 15 18 This bs bbussuysb hypathesxs anymme Tbs psusbb has been we bsmbbsbsasb bb sbms sysbsms bbsbmss had absmrbsbss and pleda an Spsmss dwemty Dbsmrbanss Tbs bbbsmsnsbs absbubsbss hypathesxs I bss bssbbsmbbsussb m the lucky msnbs mier da numemus bmss Md had pssbsmy s39ax sh and sbsus and absmrbsbss caused by na ng 1b gs meessax meb m bu DepamnentafEuvAmnmen39al 39121192 and Puhcy and mm Gimme m EVEl 01 Lecture 10 Part I Page 11 39 2 is the leading hypothesis for the astounding tropical tree species diversity Shallow roots and frequent treefalls are the source of disturbance There is also evidence that seed predation acts as a source of disturbance in this space limited community Summary Spatial variation in biodiversity We have considered in this section the determinants of local diversity ie in one relatively limited location in space To propose hypotheses we have examined spatial variation in biodiversity to identify characteristics of one location with more species compared to another location with fewer species We have not considered any temporal variation in biodiversity or other characteristics of communities but rather we ve considered either the equilibrial state of the community at that location or at least the average number of species that occur in that location over time Next we will consider the temporal variation in biodiversity and community structure at one location the topic of succession 2008 Catherine A Toft EVEl 01 Lecture 7 Page 1 Lecture 7 Predatorprey interactions 0 Introduction I Introduction 0 A Background premises and terms 0 B Patterns in nature Hypotheses 11 Simple models 0 A Form of model 0 B Functional Responses 0 C Behavior of model l t l t l t Realistic refinements of model 0 A Prey K o 1 Paradox ofenrichment o 2 Predator regulation of prey and predator efficiency 0 B Time lags predatorprey instrinsic time scales revised January 18 2008 Molles 4th edition pages 2008 Catherine A Toft EVEI 01 Lecture 7 Page 2 Lecture739 39 to p population amp PredatorPrey interactions 0 Introduction to twospecies population interactions 1 Background We could go into more detail focusing on a single species population but in fact that focus is entirely arbitrary No species exists in a vacuum All animals eat food that is often another living organism that in turn occurs in its own population Even plant populations are better understood if nutrients N P K are treated as chemoistat populations bound in the plant and unbound in the soil And of course few populations escape having predators or parasites In addition most organisms depend on cooperative relationships with other organisms for example the gut flora that helps many animals digest food and so on In the simple models we already went over where an organism gets its food and how that translates into the birth rate is all subsumed in the single symbol b We don39t model the other population which is the food that goes into 1 Similarly we don39t know what the sources of mortality are we could put them simply into d including death from predators herbivores or disease In addition mutualistic relationships with other populations could contribute to b or reduce d In other words we are talking about population interactions All populations interact with other populations In most cases food is really in the form of another population of some kind and death includes death from interacting with other species To understand the interaction we are focusing on we need to understand the populations it interacts with as well 11 Types of population interactions First let39s take an overview of all population interactions to put the rest of this unit in context Population interactions will be the focus for the rest of the quarter We specifically mean interspecific population interactions interactions between populations belonging to two different species We can classify all interactions based on the net effect on the individual members of each species or as a populationilevel effect bene t an individual benefits from an interaction with an individual of another species it eventually gives birth as a direct consequence of this benefit or it eventually survives longer as a direct consequence of this benefit population growth rate increases population size increases 0 harm an individual is harmed by an interaction with another individual Again this harm causes fewer births or more deaths population growth rate decreases population size is lower than when the interaction is not occuring 0 no effect some interactions involve no effect on one of the two species and no harm or benefit to the other We are not interested at this point in two populations that have no effect whatsoever on each other as we are taking two populations at a time Later when we build food webs and communities we will be very interested in populations that are unaffected by other species in the group 2008 Catherine A Toft EVE101 Lecture 7 Page 3 Species 1 Species 2 Exploitation Trophic interactions Predatorprey individuals of species individuals of species 2 are harmed Herbivoreylam 1 benefits growth rate of population decreases parasiteHost growth rate of population size decreases population increases population size increases Competition individuals of species individuals of species 2 are harmed 1 are harme growth rate of population decreases growth rate of population size decreases population decreases population size decreases Mutualism individuals of species individuals of species 2 benefits 1 benefits growth rate of population increases growth rate of population size increases population increases population size increases Examples predation classical predators that kill individuals and eat them carnivores insectivores etc herbivores eats pieces of plants this harms the plant in some way population growth is slowed leaves seeds etc less photosynthetic material birth rate of plantis lowered parasites don39t kill the host outright necessarily they might cause it to be weak and die for other reasons or might lower the birth rate interspecific competition includes any organisms sharing resources going handiinihand with intraspecific competition if resources are limiting there is not enough for individuals of the same intra and different inter7species using this resource Competition may be for food nutrients water space nesting sites and other features of habitat and may involve atagonistic interactions such as territoriality or not mutualism includes pollination and fruit dispersers microorganisms that live in the gut and help to digest cellulose ants that tend aphids Mutual benefits involve resources food nutrients water shared protection from predators shelterMany food webs and biomes exist as we know them only because of underlying mutualisms such as mycorrhizae which are fungusitree mutualisms without which the tropical rainforests and many coniferous forests could not exist 2008 Catherine A Toft EVEl 01 Lecture 7 Page 4 PredatorPrey Interactions I Introduction Reading in Molles Chapter 14 and parts of Chapter 6 A Background We will use the term predation loosely to mean the general 7 phenomenon We have predators in the traditional sense like lions eating antelopes or a bird eating worms or a lizard eating crickets etc However other kinds of 7 interactions are qualitatively the same such as cows grazing on grass or tapeworms in the intestines of wolves or viruses causing small pox outbreaks Your text Molles uses the term quotexploitationquot in the same general sense that I39m using quot7quot to mean simply that individuals in one population benefit somehow by harming individuals in another population In Chapter 14 Molles starts by impressing you with how complicated systems of exploitation are While I agree that Nature is wonderfully complex I will start by reducing this complexity of exploitation to the simplest form we can make it and we39ll then build up complexity from there Fundamental properties classical predator like a lion 0 1 individuals of the prey get killed and eaten This source of mortality slows population growth of the prey lower r and the prey population size is smaller than when no predator is present If the predator is not present the prey population is increased by births they might have their own prey which causes this population to grow and the prey population is decreased by deaths not having to do with the predator in question 2 individual predators eat prey and get energy and nutrients The predator needs these prey to survive they would starve without them and to reproduce energy above maintenance goes into reproduction This causes population to grow because individuals are living and giving birth Population size is much bigger with the prey than without depends on if it is the only prey very few predators eat just one prey specieswell get to that later Terms This a trophic or trophiclevel interaction Trophic refers to food When energy in the form of food passes from one population to another we call this a trophic interaction The population that the energy comes from is called the lower trophic level prey host plant The population that the energy goes to is called the upper trophic level predator parasite herbivore When we speak of these quotlevelsquot we can visualize the concept of a food chain with species linked by their trophic interactions in order of who eats whom We can conceptualize energy quotflowingquot from one trophic level to another along this quotchainquot Regulation Can predators keep the prey population below their carrying capacity The number of prey is lower when in the presence of predator than in the absence of predator In other words the predator itself is having the largest impact on the prey population as opposed to resources or some other factor eg weather It39s not obvious in any given ecological setting whether the predator of interest is actually regulating its prey or if something else is This is most obvious in cases of parasites and diseases where prey doesn39t necessarily have to die as in the case of a classical predator B Examples of real predator prey interactions Here we emphasize the population level It39s easy to watch TV programs of single acts of predation This is really a behavioral focus as in optimal foraging or an evolutionary focus as in predatoriprey coevolution the Red Queen effect whereby we look in the present at ways in which predators have evolved to capture prey and prey have evolved to escape predators Now for examples we turn to longiterm data sets where we keep track of numbers of predators and numbers of prey in a certain place over many generations worth of time 2008 Catherine A Toft EVE101 Lecture 7 Page 5 1 Laboratory example Fig 1418 The early experiments of the Italian biologist Gause who watched closed populations of Didinium rotifer a predator eating Paramecium protist a prey in a glass jar Gause found that in the laboratory predator and prey could not coexist indefintely Without his intervention one or both species went extinct in the laboratory cultures This was not very promising because ecologists at the time wanted to understand the conditions that allow predator and prey to coexist and we still do Outcome of the interaction extinction In addition to easily docurnented laboratory experiments there are numerous records of predators or prey of economic interest 2 Removal of predators and response of prey Kaibab plateau deer vs cougars wolves amp coyotes example of steadyistate regulation of deer population which we infer from what happens when the predator is removed The deer population was regulated by predators predators were removed the deer population increased until it was regulated by resources the deer population apparently exceeded its longiterm carrying capacity hurnans intervened as the new predator and keep deer well below their carrying capacityThe Kaibab Plateau is on the north rim of the Grand Canyon in Arizona Outcome of the interaction before predator quotcontrolquot coexistence of predator and prey regulation of the prey by the predator roughly steadyistate population sizes 3 Hudson Bay fur company or other hunting and forestry records show longiterm cyclic behavior of populations A population cycle is defined as having a constant period time between any two points in the cycle for example between two peak population sizes and amplitude the difference between the highest or peak and lowest population sizes In real life cycles the amplitude varies a lot but the periods are regular 0 A Famous Canada lynx snowshoe hare 9 to 107year period Fig 1414 B Muskrat fox etc 9 to 107year period but the amplitude is especially variable C Red Grouse shot on Scottish moors W a nematodeigrouse interaction with a 9 to 107year period D Pine moths and Larch moths 9 to 107year period E Lemmings grass ilemming interaction 3 to 4 year period Shelford farnous ecologist studied se 0 F Shrewsiinsects7 miceimouse food or mouse predator 3 to 4 year period Remarkably many cycles are on either a 3 to 4 year period or a 9 to 10 year period even considering vastly different organisms What could be involved to create such a universal pattern Also most of these examples are of populations at high latitudes What kind of environment occurs at high latitudes and what effects could this environment have on populations Outcome of the interaction coexistence of predator and prey regulation of prey by predator population sizes exhibit true quotcyclesquot with a regular period and roughly regular amplitude 4 Hurnansiplagues amp parasites Hurnan populations were apparently regulated by parasites for long stretches of human history Historical records show irruptive population behavior not on a regular cycle plague comes and population size goes down after the plague population growth resurnes its former exponential rate Outcome of the interaction coexistence of quotpredatorquot and quotpreyquot and regulation of prey by predator over time although local interactions might involve extinction of prey or predator or escape by prey o regulation by predator population sizes of prey and predator tend to be locally quotirruptivequot 2008 Catherine A Toft EVEl 01 Lecture 7 Page 6 5 New predators introduced into new prey populations humans overexploiting fisheries of various kinds of real fish and of whales We see downward trend in the prey population new level of regulation and potentially extinction Examples of extinction from human predation as opposed to competition or habitat destruction include passenger pigeon Eskimo curlew dodo great auk some of the Galapagos tortoises giant ground sloth and marnmoths Humans have caused the near extincition of many fisheries Outcome of the interaction often extinction lack of coexistence predator drives prey extinct by over exploitation Summary Review examples of population behavior in chapters 9 and 14 and examples shown in lecture Patterns of real populations resulting from predatoriprey interactions that we will want to explain 0 l Extinction 0 simple laboratory experiments 0 introductions of new predators 2 Coexistence o constant population sizes of prey and predator 0 variable population sizes I irruptive I true cycles 0 regulation What are the categories of explanation Hypotheses for what causes particular population behaviors can be placed in two broad categories 0 l Extrinsic factors from outside the population environmental factors that affect the population immigration and emigration of individuals from outside this local population 2 Intrinsic factors generated from the very characteristics of the population itself parameters of birth rates death rates and other characteristics of the two populations and importantly the interaction between the two populations For example what makes some populations show periodicity regular fluctuations Is the periodicity extrinsic that is caused by an outside fluctuation like sun spots or El Nino Or is the periodicity intrinsic that is caused by the nature of the predatoriprey interaction itself We really need to analyze some models to generate some hypotheses and possible mechanisms for periodicity of population sizes 2008 Catherine A Toft EVEl 01 Lecture 7 Page 7 II A simple model A Form of the model Once again to learn how the two populations will behave when they interact you need to use a simple model Only a model will allow us to tally all the effects of prey births prey deaths and predator births as a result of this interaction See your handout 1 Verbally we want to keep track of what is in each box contributions to births and deaths of prey and predator respectively Then we put symbols for each of these ideas into a simple model to see what this model can tell us about predatoriprey population interactions Important points 0 1 We want to keep track of the number of prey and predators that result from their interaction with each other Prey 2 The prey can grow as any population would in the absence of the predator We don39t care in this viewpoint about whether the prey39s food is a population or not We39re just focusing on one interaction taking two populations in a vacuum instead of one as we did earlier 3 As a result of the interaction with the predator prey die when they are captured and eaten We could express this as part of little r and the death rate but we39re going to pull it out here for the sake of understanding it and look at how this death rate depends on the number of predators o The capture rate is of special interest to us because a lot of the predator39s behavior goes in here How the predator captures prey will determine how many it captures under certain conditions We call this the functional response ie all the predator39s behaviors that determine how many prey it will capture per unit time units number of prey capturedpredatortime 0 Also the prey are captured in proportion to how many predators there are so we need to plug in the number of predators Predator 0 4 The predator population grows in proportion to how many prey are captured per unit time The number of new predators with time is called the numerical response The numerical response is said to be a function of the functional response The number of prey per unit time eaten will be converted into offspring The conversion rate efficiency will be less that 100 because the prey will be used for the mother39s maintenance and the offspring39s growth In other words typically many prey will be needed to produce one predator offspring 5 The numerical response is a more explicit way of writing I in r bd You multiply times the number of predators there times the percapita birth rate to get the number of new predators 6 The predators die in the absence of the prey This can be viewed in one of two ways This can be viewed as the death rate similar to the d in r bd Or it is sometimes viewed as rate at which predators starve to death if there are no prey Let39s just consider it to be the simple death rate which will usually be independent of the prey 2008 Catherine A Toft EVEl Ol Lecture 7 Page 8 2 Mathematically We will simply give this ideas symbols and use algebra amp calculus to understand the population behavior See handout Edenote about symbols Your teXt Molles gives this model different symbols p 3345 I39m using another et of common symbols that are either traditional e g N and r for prey or a for functional response or uneumonic which means that they are the first letter of what we call them eg P for predator c for conversion rate d for death rate I find that using bunches of subscripts e g Nb and Np for number of prey or host and predator or parasite makes it harder for me to remember and keep track of the symbols you are elcome to learn the book39s symbols if yg prefer them Additional points about the model 0 l The prey will grow exponentially in the absence of the predator We are only going to do this at first to see what happens We want to isolate the effect of the predator to see if the predator can regulate the prey population So we don39t want to put in densityidependent regulation of the prey Thus this r is the familiar intrinsic growth rate rmX of the prey 2 We will use a to mean the capture rate lt39s constant which may be unrealistic it a minute we39ll consider more realistic but more complicated forms of the capture rate Formally aN is functional response Here prey and predators burnp into each other randomly NP just like the optimal forager that we already considered 3 Prey will therefore die at a rate aNP which gives you the probability of a prey individual encountering a predator NP and the probability that once encountered the prey will be killed by the predator a In a sense this meets the criterion of regulation because the total number of prey killed depends on the predator density 3 The symbol c will be our conversion rate So caN is the numerical response This is the per capita rate at which predator offspring are produced by each predator or the predators birth rate 1 4 The symbol d will be the predator death rate So the predator39s intrinsic growth rate rpmd caN d Thus the prey controls the predators population we can ask when does the predator control the prey B Functional response Before we look into the behavior of this model let39s consider the functional response The functional response is one of the most important features of predation because it is the predator39s behavior and our chance to consider the biology 3 general kinds of functional responses Molles Fig 621 Lecture handout We could write equations for any of these but the only one I want you to remember is the simplest case aN or Type 1 functional response IMPORTANT NOTE don39t confuse these with survivorship curves I ll Functional response curves are plotted in terms of number of prey captured per predator per day versus prey population density 0 Type I is linear In its purest form the predator never satiates The more prey there are the more it eats This does not seem to apply to most predators although it may apply to many some of the time see your book Fig 621 top Type II The number of prey levels off because the predator satiates is full and needs to digest or it takes the prey a lot of handling time with each prey At some point handling time or digestion time is the limiting factor Even if there are more prey than that the predator is eating them at the fastest rate it possibly can so at that point the prey caught per predator per unit time levels off at a maximum rate However the important point is that approaching the asymptote the slope of the mction is maximum at lowest prey density and only decreases gradually from there 2008 Catherine A Toft EVEl 01 Lecture 7 Page 9 Type III The number of prey taken levels off for exactly the same reason in the type II curve However something different occurs at low prey density At low prey density the predator may ignore the prey or can39t find it Then at some higher prey density the predator catches it at a higher rate This is exactly the prey switching we already covered Prey switching may be caused by a search image Or it may be that there are a fixed number of hiding spots and when prey get more common they can39t all hide so the predator finds and eats them at a faster rate In other words the slope of the functional response is not maximum at lowest prey densities but rather at intermediate prey densities While this may seem like a fine point to you the resulting population behaviors are vastly different for Type II and Type III functional responses C Behavior of the model lecture handout Fig 1417 1 The Volterra model uses a type I functional response lecture handoutthe simplest with the least biology As before we start out with the simplest possible model to see what happens We will add more complexity only if it39s necessary to explain what real predatoriprey populations do 2 You want to know what happens at equilibrium At equilibrium nothing is changing so the growth rate of both populations is zero averaged over time dNdt 0 and dPdt 0 Why do you want to solve for this equilibrium Answer because you want to know how the interaction comes out You want to know what happens in the long term whether the predator and coexist and whether the predator can regulate the prey population So you see how your model behaves when numbers of predators and prey are at a steady state 0 a The equilibrium number of predators P When dNdt 0 then rN aNP 0 You solve for the number of predators P Because we39re defining this as the quotequilibriumquot number we use the notation P We use the prey population equation to solve for the number of predators because the amount of food prey population size determines the number of predators aroun dNdtrNaNP0 rN aNP r aP P ra 0 b The equilibrium number of prey N When dPdt 0 then caNP A dP 0 You solve the predator equation for the equilibrium number of prey because we are looking for the conditions under which the predator regulates prey population In other words the predator population determines the number of prey around dPdt 0 caNP dP 0 caNP dP caN d N dca Summary We are asking can predator and prey coexist AND can the predator regulate the prey population So we solve the model of 2 coupled equations for their joint solution with both populations at steady state the average number of predators and prey are neither increasing nor decreasing with members of both populations around coexistence neither population goes extinct with numbers of prey 2008 Catherine A Toft EVEl 01 Lecture 7 Page 10 being determined by the numbers of predators and vice versa Once we do that we need to see how the model behaves to see if it captures the qualities of real predator and prey interactions that we summarized above 3 To understand the behavior of the model visually we can plot out the numbers of prey against the numbers of predators This is called a phase plane which is when the state variables N and P are plotted against one another Time is not on the plot but you can see time when you draw arrows from one point on the plot to another Fig 1417b On a phase plane you plot the zeropopulation growth isoclines Zero populationigrowth ZPG isoclines on a phase plane are where the growth rate of each population is zero There is a prey ZPG dNdt 0 isocline and a predator ZPG dPdt 0 isocline On one side of this line the population size increases dNdt gt O or dPdt gt 0 and on the other it decreases dNdt lt 0 or dPdt lt 0 n quotisoclinequot a line where everything is equal iso equal cline line You look at isoclines every night on the news during the weather report Isoclines on a weather map plot everywhere the temperature is equal 0 some one value like 70 or everywhere the barometric pressure is some high value or some low value 1391793 E Eam lt 9g llelEYQQQDJSQ011119 9 19I139 leEQEXVPBUiSQQEIElEQDIESEYQU7 Fm Look at the graph to see what regions the prey is increasing and what regions the prey is decreasing and similarly for the predator To make this part less confusing refer to your lecture handouts pp 29730 W99 on understanding phase plane trajectories Where the two ZPG isoclines cross you have an equilibrium point if there is one In other words at this point both populations are jointly at steady state neither increasing or decreasing that is dNdt 0 and dPdt 0 In this Volterra model things are more complicated however There is not only one possible equilbrium point but there is the possibility of stable cycles Fig 1417 0 1 There is an equilibrium point at the crossing of the two lines If the system is here population sizes of the prey and predator will be constant 0 2 However if the population sizes are disturbed from this point they are pushed into cycles The prey population size increases and decreases with a regular period and amplitude The predator population size also increases and decreases with a regular period and amplitude but the peaks highest population size and troughs lowest population size of the predator lag a bit behind those of the prey Fig 1417a See the picture of nested cycles and plot of population size in lecture on the phase planes see also the lecture handout book Fig 1417b In the Volterra model the trajectories look like eggs or ellipses You read it like this When you have this number of prey you get this number of predators and when you get the number of predators changes you end up with that number of prey it translates into population size plotted against time In other words these lines on the phase plane can be viewed as trajectories in time This model is so far too simple to be very realistic but it does produce one important behavior exhibited by more realistic models ijredatorprey interactions have a natural tendency to oscillate cycle We haven39t seen cycling behavior before in the simple models we39ve gone over in class Populations may cycle for other reasons but predatoriprey oscillations are common in nature as we saw in the examples These cycles aiise from the very nature of the interaction the predator population size depends on the size of the prey population and the prey population size likewise depends on the size of the predator population This interdependency produces a pattern of cycles The predator population pushes down the prey population fewer prey makes the predator population go down when the predator population is down the prey can increase when the prey increase the predators can increase and so on The mechanism of the tendency to oscillate in the model is an implicit time lag The predator is lagging behind the prey thus the two populations in effect overcompensate or overreact to any change in the other 2008 Catherine A Toft EVEl Ol Lecture 7 Page 11 Any kind of time lag whether due to predation or other factor will produce cycles in population size Even with the simplest possible model we now have an hypothesis for population cycles see 111 D as well We can hypothesize that time lags of both intrinsic due to age structure time to grow to maturity time to react to the other population and extrinsic seasonal environment means that breeding takes place only one part of the year and so on origin We can pursue this hypothesis in more complex models and with data collected from populations in lab and in nature More complex models than we will go over in this course predict that the period of the cycle should be approximately 4 X the time lag T ie 4T This prediction is interestingly consistent with the observed periods of high latitude cycles 34 years for small mammals suggests a 97month to liyear time lag and 97 10 year cycles of large mammals suggest a time lag a little over 2 years These time lags are consistent with the life cycles of these species and the seasonal environment in which they live So you don39t need something exotic like sunspots to explain these cycles you need only a seasonal environment and some realistic demographic parameters in your model Next we explore some more realistic features to add to the simple model that we just went over III Realistic refinements of the simple model Four factors that influence the inherent tendency of predatoriprey interactions to oscillate are 0 A Prey carrying capacity K 0 B Predator efficiency 0 C Type II or Type III funcational responses 0 D Prey vs predator relative values of their intrinsic rate of increase A Prey carrying capacity We started out with no limit on the prey population because we wanted to see what the predator alone would do Obviously most prey species will have a carrying capacity set by their resources so what effect does this have on the tendency to oscillate Prey carrying capacity counteracts the tendency to oscillate lecture handout The reason is very simple and very intuitive A prey carrying capacity puts a ceiling ie a limit from outside on the prey populations oscillations and so this also puts a limit on the predator populations oscillations and the ability of the predator to drive prey oscillations Lecture handout Mathematically this appears as a sloping prey isocline with an intercept at NK 0 P rliNKa this makes the line slope down You can see how the oscillations bump into a ceiling and this causes them to cycle inward So after a disturbance we see decreasing oscillations to return to a constant population size We call this damping oscillations By damping we mean that they get smaller through time Paradox of enrichment This effect leads to something called the paradox of enrichment The prey zeroipopulationigrowth isocline gets a steeper slope and intercepts the Niaxis K at lower N then the prey and predator 2008 Catherine A Toft EVEl 01 Lecture 7 Page 12 equilibrium population sizes are closer to the prey39s carrying capacity Near the prey39s carrying capacity the oscillations are very small to begin with and population sizes settle very quickly to constant numbers of prey and predator Say you somehow enriched the preys habitat Then you would move the prey39s carrying capacity much higher than the current population sizes This would allow room for the oscillations to occur The population sizes could swing widely again just as if there were no prey K The paradox of enrichment was first discovered in aquatic systems in predatoriprey interactions between algae and daphnia and other species which eat the algae When pollution enriches the aquatic habitats the algae and daphnia populations would go wild Some extinctions even occurred during the extreme amplitudes of the uctuations See the biggest egg on the Volterra model39s phase plane This pattern is called a paradox lmportantly the use of this term which is judgmental reflects human values We think that fertilizer and more food is good and extinction is bad But this isjust the way we as humans would see it Otherwise it is a simple and straightforward relationship high input of resources for the prey perturbs the interaction and removes the stabilizing effect of a low ceiling carrying capacity on prey numbers B Predator ef ciency The prey K is imposed from the outside on the interaction But exactly the same effect as the paradox of enrichment can come from within the predatoriprey interaction itself The predator may be more or less efficient as values of a the simple Type I funcational response varies If the predator is very good at finding and catching prey high a then the predator population can depress the prey population well below its carrying capacity See your handout Playing with predatoriprey ZPG isoclines lecture handout Once again the further the prey is held below its K the more room for oscillations More importantly we can see the meaning and effects of regulation of the prey population by the predator population The difference between N and K is the degree of regulation The higher the value of a the smaller the value of N dac the more N is below K and the greater the Egree of regulation C OPTIONAL An even more realistic model is to incorporate a type II functional response and K and vary the parameters of the response to see what happens I won39t go into the mathematical details because this is the topic of a more advanced course but you get stable cycles with a constant period and amplitude This type of cycle is stable because it is resilient to outside disturbances No matter what happens the predator and prey populations return to oscillating with a constant period and amplitude D Prey and predator intrinsic growth rate This effect has a different mechanism If prey and predator intrinsic growth rates are vastly different the system may get out of synchrony causing cycles As the prey intrinsic growth rate gets faster all else equal the prey can shoot ahead of the predator In other words if the prey intrinsic growth rate is sufficiently faster than the predator populations then the predator is slower in catching up to changes in the prey population size And vice versa also happens Predator can overrun prey knock it way down then it takes the prey a long time to recover Either effect exaggerates the time lag The bigger the time lag the bigger amplitude and longer period of the cycles 2008 Catherine A Toft EVEl 01 Lecture 3 Page 1 Lecture 3 outline Physiological ecology Readings liMolles Chapters 46 and 9 see lecture notes for specific pages to emphasize I Background amp overview 0 A Internal environment 0 B External environment amp organism s response conformers v regulators 1 Water 0 2 Temperature 11 Basic Concepts 0 A Ecophysiological limits 0 B Consequences Ecological and evolutionary significance of limits 0 1 Frog example 0 2 Plant example 0 3 Fish example 111 Application desert ecophysiology covered in section Wed Jan 27 1999 0 A Background 0 B Krat example 0 C Desert Iguana IV Slides revised January 11 2008 Molles 4th edition pages Lecture 3 Physiological Ecology Last lecture we considered broad pattems in the global environment that determined the character of whole ecosystems or biomes Today we will take those same physical factors and go to the opposite end of the spectrum to look at how individual organisms cope and interact with their physical environment NOTE Ecology as a science hopes to explain broadest pattems in ecosystems by building up from individuals if we understand the quotbuilding blocksquot we hope to understand the whole I Introduction and Overview A Internal environment It is useful to review the very basic fundamental life processes that must be conducted under thermal and osmotic conditions that support life 0 1 Obtaining and assimilating energy For plants this means photosynthesis review Ch 6 135 138 for animals it means feeding on organic molecules produced originally by autotrophs This energy is typically stored in various forms of C carbon in organic molecules known as carbohydrates This is true even for chemoautotrophic bacteria that get energy originally from nitrogen or sulphur containing compounds Figs 617 and 618 0 2 Gas exchange for respiration all organisms and photosynthesis plants C02 and 02 These gases can pass only across wet cell membranes ie at saturation with water 3 Water osmotic balance all living metabolic processes occur in aqueous solution The exact concentration for these processes is critical and subject to natural selection Osmosis is the movement of water molecules across a semipermeable membrane 4 Uptake plants animals and excretion animals of nitrogen the byproduct of using proteins to build living material 2008 Catherine A Toft EVEl 01 Lecture 3 Page 2 These are the 4 physiological processes living organisms must do to survive and reproduce and thus these processes determine an organism s fitness We will spend time on some of these requirements and how organisms meet these needs in a given environment Importantly the 4 processes are often highly interrelated For example how an organism excretes nitrogen will depend on its osmotic environment or how an organism maintains proper osmotic concentration will often depend on the temperature of the environment in which it occurs Moreover the organism s evolutionary background determines the means by which it might solve a problem such as how to excrete nitrogen or how to maintain osmotic balance in a hyperosmotic environment In addition there may be several ways to solve a problem several options open to a given organism either in evolutionary or ecological time With this lecture we will begin to consider the costs and benefits or disadvantages and advantages to a particular solution for a particular organism in a particular environment We also must consider all living organisms face constraints either constraints inherent to all life processes such as gas exchange must occur across a wet cell membrane and water carmot be actively transported across cell membranes 0r constraints specific to an organism because of its evolutionary heritage for example all mammals excrete urea as their primary nitrogenous waste Ecologists consider these costs benefits and constraints to understand Why a particular organism has adopted a particular solution We ll consider a number of examples in the next few lectures B External environment and the organism s response given the above The two primary physical factors organisms need to deal with are 1 Water 0 2 Temperature 1 Water Molles Ch 5 Water balance water either leaves or enters the organism by osmosis along concentration gradients and by evaporation along water vapor deficit gradients p 110113 For many marine organisms there is no quotproblemquot with water balance Life evolved first in the sea and many many marine organisms simply let water reach an equilibrium by osmosis These are osmoconformers While this is very easy being an osmoconformer definitely puts limits on the environments organisms can occupy basically full strength sea water or parasitic invasion of other organisms Such an organism has no exibility and little control over its own intemal environment So as we shall see there seem always to be both advantages and disadvantages to the ways in which organisms meet ecological challenges The remainder of organisms are osmotic regulators Many organisms live in other kinds of osmotic environments for one reason or other They invaded freshwater from the sea and land ie air usually from freshwater vertebrates and reinvaded the sea from those environments These organisms face a net water loss or net water gain so that life would be impossible in those environments without some kind of regulation of water balance Organic molecules must be in certain concentration for life processes to occur if too dilute metabolic process do not occur fast enough if too concentrated molecules are not properly dissolved in water and change states bringing metabolism to a halt Table see 5 113 occurs gets water enters osmosis of water osmosis or or consumes leaves organism by osmosis or loss of water 2008 Catherine A Toft EVEl 01 Lecture 3 Page 3 Question what are the most extreme osmotic environments that you can think of Review principles from Bio Sci 1 that will tell you which way water goes in or out in which type of environment Summary Osmotic conformation is the quotcheapestquot way to go ecologically and physiologically speaking an organism does nothing Osmotic regulation is more expensive requires metabolic energy and new structures need to be built but organisms that can control their intemal environment regardless of the external environment can take advantage of ecological opportunities to use new unexploited environments This observation introduces an important concept HOMEOSTASIS Smith pp 334 maintenance of a relatively constant intemal state under a much wider range of physical and environmental conditions The trend in evolution of life on earth is increasing homeostasis as you have learned in a beginning BioSci class 2 Temperature Molles Ch 4 Life is possible when water is in a liquid state making the 1 Q LOWER temperature constraint about 0 C or at most a few degrees below supercooled ocean water primarily ie 1 to 2 C 2 UPPER temperature constraint temperature at which proteins and other organic molecules retain their integrity For most things this is about 50 C There are some bacteria however that can live in higher temperatures up to over 100 C under the pressure of deep ocean water near volcanic vents While these are the extremes within this range metabolic processes occur best at certain temperatures Shortly we shall consider rigorously in ecological and evolutionary terms what might be intuitively considered quotbestquot Again there are temperature conformers and temperature regulators Molles pp 91101 Two sets of terms to discuss this dichotomy Molles p 93 Ectotherm organism s body temperature is determined by outside environment 0 Endotherm organism generates heat internally to determine body temperature endothermy is not commonit requires a tremendous amount of metabolic energy 0 Poikilotherm associated with ectotherm body temperature varies Homeotherm 39 with 39 body 1 constant 2008 Catherine A Toft EVEl Ol Lecture 3 Page 4 These two sets of terms deal with highly related concepts but they are not synanynwus We know that necessarily endothermshomeotherms the latter nearly always are regulators we don t quot know if l quot quot are or regulatorsmost of the organisms in this category are a bit of both What are examples of organisms in each category What examples can you think of for each of the four cells in this table Organisms in box 1 are the thermoconformers and organisms in box 4 are all thermoregulators In section we will consider the advantages and disadvantages of each side of this dichotomy Importantly you should consider that both conformers and regulators have both advantages and disadvantages One strategy is not clearly better than the other Summary Much of physiological ecology for both plants and animals can be reduced to regulation of these two factors temperature and water balance and of course you see that they are not independent Obviously the way organisms regulate body temperature and osmotic concentration depends on the environment in which is it found Also to understand an organism s ecophysiology we need to understand not only the organism s environment but also its life history morphology and evolutionary background 11 Basic concepts in physiological ecology Examples of physiological limits to living organisms are lethal limits avoidance limits and optima Criteria for judging these limits are primarily tolerance occurrence and performance A Ecophysiological limits Lecture Handout 1 Lethal limits The crudest way to look at requirements of temperature and water balance is to find the extreme upper and lower points where the organism simply dies This is of limited interest to an ecologist Tolerance limits Also referred to as tolerance limits the animal can tolerate conditions within the lethal limits 2 Avoidance limits Animals can move around With sessile animals and plants their offspring can move round Sessile organisms can also grow asexually which in a longer time frame is a type of movement involving quotchoicequot by the organism Thus you might test for the limits of the environment that an organism will seek out either directly by behavior or indirectly by differential growth or dispersal of offspring These limits will likely be much more narrow than the tolerance lethal limits 3 Performance optimum pp 8789 You can also examine the environment in which the organism does quotbestquot quotBestquot is measured in terms of maximizing quotperformancequot in some area something that leads directly or indirectly to obtaining energy best intemal physiology performance reproductive output and so on Ultimately the measure of performance becomes the organisms fitness determined by its ability to survive and reproduce B More concepts Ecological and evolutionary significance of limits 1 Frog example Performance of a frog jumping ability This type of study always gets the attention of senators who control funding for scientific research or entrants of Mark Twain Days frog jumping contests Because frogs are ectotherrnic poilkilotherms their ability to jump muscle fiber twitch speed is determined by the frogs body temperature 2008 Catherine A Toft mm 14msz ooNcEn F m u mama duu lv wnh pathmum cmum my ammymynrrwmm mannawan ahlun camewtrrym m m heme my mama mu m allHf nmapraiamr mm wwalmdlvpmdnmnn 3211mm cm awedumx mm ynaanmnmm m39nmnal defamer szrmancz mm mpm um i Survivalw Envuvnmzmal variable 4 mum cmdmnns Hm m 51mmme vanahle nnmzrsus mam mm max mm um and mum xqwemuem y unable nxpnmmm m xs lull gamma ni mQrwpmdnmnms m mum mummmnn nuauxms mm mm alsn max mm mm animus us Fmblenndn mamml y Emmirump n mmmmmxal cmdmmdsrby de nxnnn m m Fumble pummmce ncmls mly ma vpnmnm cmdmms 1 e m mumst rm nimvmmmmxal sandman 1 mm mm puma my mnmm mvzmi sum cmwpts amnuhe ewphysmlnly n llmts Tn mural Plats nmam may an air Themmzxaparcdnfan Lumena1 n warmqu mammwm de m ca hepmmna ylanzr yusxdqlmdm mm mamaarms am m an autumn We an memem mm was nfaplmx39s pefmmmce m H mm m phnxnsymms 3 mm max 1 nhvmnsly mm m mm mm m menu S ahmly m snrvwe and manna L um mm may m mmmnmmm s mmn IyFICany w ns m nicoz c mm m m 131 m an upmmmammmymm Exam mg mprnmmce m aw mm mm EVElEIl Lecture 3 Page 6 b temperature The rate at whlch a plant conducts photosynthesrs or any other metabolrc Thls reaction at a gwen temperature We can look at that as a performance curve whlch ls unrmodal Molles pp 90791 Frgs 4 10 and 4 ll Thls example rllusuates the concept of performance m plants and Upmmm rnpera ur l r photosynthesrs by our deflnltlon of opumum Valley rouunely populztlons l However ln lecturer well see a better gaph of th5 study whlch appears m Smth Hg 5 4 p 84 photosynthetrc rate We need to speclfy our unrts of i ii those rates m a meanrng ul my but m a general plot e w photosynthesrs exceeds the energy used m respuatron mlmnlrmwv a plant has a net garn of energy that rt can use for growth and reproducuon Thls net garn m energy xed from the sun ls what we speclflczllyman by primary production or primary productivity We can plot a c ve for pnma producuon and show MMquot s c s um te ture or morsture level measured m mter avarlable to the plant somehow that corresponds to the mammum rate of pnmary productron emu pm nmumuy We om now vlew the relatronshrp between prrmary productwrty and cllmzte r e temperature and preclpltzhon on a global scale measured m many dlfferent plant communmes on Earth up to 4 M of W m tota a ual mlnlel m the wet troprcs and up to 30 C average weekly temperature mum Cathmm A m EVEl 01 Lecture 3 Page 7 Thus plant primary productivity increases both with moisture precipitation and with temperature world wide as a result of two physiological factors 1 at higher but within optimum limits temperatures the plant s metabolic processes can occur on average at a faster rate and 2 with both higher temperature 30m BIJUEI ii it IE 5 a e a a h h LL LL qunjnjl Precipi atinn mm Tempemtum DC and higher moisture in the environment plants have higher rates of gas exchange and evapotranspiration because stomates can stay open more of the time and thus higher rates of photosynthesis and energy fixation Keep in mind that the broad empirical patterns observed in the above figures represent adaptations of plant species in each climatic region and should not be directly applied to any given plant species e g if you moved a cactus to the wet tropics it would not necessarily fix more energy under conditions for which it is not adapted See the next graph Ecophysiological limits in two dimensions humidity and temperature ff quotHum xxquot x E f E pruduc nn E m E E II139CI FquotEh L r K x Ehmrival Humiclitjr Each species will exhibit an optimum range of conditions within which reproduction occurs that is a result of adaptation to the particular environment in which that species occurs Temperature and moisture can be combined into a single index of evapotransiration Fig 152 p 345 In this graph you should notice 1 that net primary production and actual evapotranspiration are highly correlated notice that primary production is plotted on a logarithmic scale and 2 that net primary production and evapotranspiration are highly characteristic of specific biomes In other words the physiognomy of the vegetation at a given location is determined by that location s climate by both ecological and evolutionary mechanisms See the Appendix of Lecture 2 for a primer of evapotranspiration 2008 Catherine A Toft EVEI 01 Lecture 3 Page 8 Summary so far 1 We see that conditions under which an organism can survive are not totally equal Importantly there is a range of optimum conditions that allows the organism to reproduce this range of optimum conditions is that which maximizes the organism s fitness 2 For many organisms the physical environment is multidimensional in particular most organisms require a suitable range of conditions of both moisture and temperature 2 dimensional and there may be more factors that need to be taken into account 3 Fish example remember that fish are ectothermic Two and are raised in two different thermal 100 C and 20 C trout This example illustrates two additional principles a Organisms become evolutionarily adapted to a specific range of physical environments Trout are adapted to cold water and bass to warm water The mechanism involves specific enzymes which work best at certain temperatures By natural selection frequencies of genes producing temperaturespecific enzymes change until the average fitness in that population is maximized in that temperature environment b Organisms can acclimate or acclimatize Acclimation Acclimatization or is the process of adjusting homeostatic mechanisms to perform under specific physical conditions This process is a form of phenotypic plasiticity Physiologists also call this quotAdaptationquot but we can t because it s different from evolutionary adaptation Most organisms have a range of physical conditions to which they can acclimate but there is a limit to quot 39 set by 39 t 39 Note on terminology I don t care how you use the terms acclimate or acclimatize in this course Some prefer that acclimate refers only to laboratory experiments and acclimatization refers to what organisms are doing in nature Normally I prefer shorter and simpler words for things and as few special terms as possible I personally will use quotacclimatequot only The mechanisms for the above pattern in rainbow trout and largemouthed bass is determined by temperature specific enzymes Fig 48 pp 87 Evolutionary adaptations natural selection shifts the frequency of alleles coding for temperature sensitive enzymes If selection is strong enough alleles coding for temperatures not normally encountered by the organism may be lost from that population Let s consider a hypothetical mechanism of temperature sensitive enzymes from enzyme 1 that functions at lowest temperature range to 4 that functions in the highest temperature range 1 2 3 trout possess a subset of the enzymes that work in coldest to intermediate temperatures whereas 2 3 4 bass possess a subset of the enzymes that work in intermediate to hottest temperatures We can introduce two specific terms to describe the pattems in the above table 2008 Catherine A Toft EVEI 01 Lecture 3 Page 9 Acclimation p 89 The ratio of enzymes 123 etc might be adjusted metabolically according to the range of temperatures encountered by that individual Enzymes are produced by the individual as needed depending on the water temperature at that time It may take a few hours or days for the enzymes to be produced but an individual can eventually produce the exact ratio of enzymes optimal for the thermal environment at any given time Adaptation By evolution alleles that code for enzymes that are rarely or ever needed are lost presumably because there is some cost to possessing extraneous machinery for producing the temperature sensitive enzymes So the trout that live in cold water have no quotneedquot for enzyme 4 and eventually the alleles for this enzyme are lost from the population etc Another example in humans Example of adaptation by Inuit people quotEskimoquot These people live high in the Arctic Circle circurnpolarly with settlements in both Siberia and North America their ancestors have lived in this climate for tens of thousands of years They have subcutaneous fat over entire body including fingers and more blood supply to extremities opposite of immediate reaction to extreme cold shunt of blood to body core to prevent cooling so that they can use their hands without gloves to hunt and fish even in the coldest weather Inuit also have more roundshaped bodies to minimize their surfacevolume ratio why what is the advantage to them Example of acclimation by longdistance coldwater swimmers By diet and training they can add more subcutaneous fat lower their body temperature and adjust ratio of musclefat for neutral buoyancy The ultimate in ability to acclimatize may be Lynne Cox the first person to swim the Bering Straits from Alaska to Siberia in water ranging from 38 F to 44 F An ordinary unacclimatized person could live perhaps 30 minutes in water this temperatur but Cox did the swim in about 2 hours She was able to acclimate ie change her phenotype to tolerate cold environmental conditions better than the Innuit people who have a genotype adapted to tolerate colder conditions on average than Cox s genotype An Inuit person would have to acclimate just like Cox did to be able to swim in the Bering Straits cold water perhaps this acclimation would take less long for an Inuit than for Cox However the ability of individuals to acclimate is quite impressive and may more than compensate for their genotype 2008 Catherine A Toft EVE 101 Lecture 2 Page 1 1 Unit 1 Individual Ecology A The Earth s physical environment and world vegetation B Physiological ecology of plants and animals C Behavioral ecology of animals Lecture 2 outline Principles of the Earth s physical environment and World Vegetation I Fundamental properties of the Earth s environment 39 A Background B Solar Radiation 39 C Global atmospheric circulation patterns 39 D Precipitation 11 Consequences for ecologists climate and world vegetation 39 A Climate 39 1 Latitudinal patterns 39 2 Effect of topography 39 B World vegetation 39 1 Determinants of primary productivity 39 2 Classification of the world vegetation biomes 2008 Catherine A Toft EVE 101 Lecture 2 Page 2 Introduction to next unit Individuallevel ecology The next unit until the first midterm will cover the first level of organization in ecology that of the individual organism This unit will cover aspects of the physical environment particularly how the individual s physiology is adapted to the physical environment and aspects of animal behavior particularly feeding behavior and mating behavior These concepts will build up to understanding the process of population growth Note in the lecture notes texts other than Molles are referenced All these text books are on reserve at Shields Library These references are optional but they do provide clear and useful presentations of material not covered as well by the Molles textbook Lecture 2 Principles governing the Earth s physical environment and World Vegetation Readings Ch 2 1345 Ch 3 4853 Ch 18 41218 4245 The physical environment has fundamental effects on living things so we ll go over it first By quotphysical environmentquot we mean the general parameters of temperature light atmosphere moisture and climate and so on in which an organism lives ie those factors not arising from other living organisms We start with an overview of the planet Earth and its physical environments I Fundamental properties of the Earth s environment A Background The goal of this section is to understand the causes of and variation in climate on the planet Earth Climate is defined as the annual pattern of temperature and precipitation at a given location To get a feel for what this means look at your textbook Fig 27 p 18 In section we will cover how to construct and read a Walter amp Leith climate diagram which is the most ecological way to represent climate because this diagram is relevant to a plant s physiology As we shall see patterns in climate are vital to understanding the distribution and abundance of organisms on this planet Climate and indeed the development of the Earth s biosphere and the forms inhabiting it are profoundly effected by three general components of the physical environment on Earth 39 1 energy in the primary form of solar radiation which permits energy for life processes and which provides a temperature range in which life can exist H20 is in liquid form 39 2 atmospheric gases which also permit life as we know it oxygen 02 carbon dioxide C02 and nitrogen N2 which buffer living things from outer space and which form a transport system for water and energy and 2008 Catherine A Toft EVE 101 Lecture 2 Page 3 3 water which is the universal quotsolventquot for life Metabolic processes must take place in an aqueous solution except for some strange viruses These three physical components of the Earth39s biosphere that permit the biosphere are not independent or static They interact with the Earth39s 39 shape sphere gravity rotation on its axis 39 rotation around the sun and 39 angle of tilt relative to the sun to form a complex mosaic of physical environments on the earth and to produce climate Interactions among these physical properties of the planet The earth s atmosphere exhibits complex patterns of circulation because of 1 differences in solar radiation input due to 39 latitude shape of the Earth and 39 season the tilt of the Earth on its axis 39 2 the Earth s rotation daily produces not only daily variation in temperature but importantly forces on the atmospheric gases 39 annual produces seasons above These features result in patterns of global climate which the environments that organisms have to adapt to as we shall explore in Lecture 3 In contrast weather means the physical properties of atmosphere at any given moment ie 1 day at a given location in particular the temperature moisture barometric pressure and surface winds In the first half of this lecture we will develop how these features produce climatic patterns on the planet and what those exact patterns are I39m not going to go into the details of why these physical patterns occur that is the topic of a physical geography course or even a course in physics and I39m not competent to explain the physical principles to you Instead I will summarize the major global patterns in the physical environment that are important in determining ecological patterns as much as you would need to know as an ecologist I will highlight the material in Chapter 2 that I would like you to know and read more on your own On reserve the 5th Edition of Pianka39s Evolutionary Ecology has an especially nice concise explanation in Chapter 3 pages 41 51 2008 Catherine A Toft EVE 101 Lecture 2 Page 4 B Solar radiation Solar radiation is the key to understanding the Earth39s climate indeed it is the very energy that allows life to exist on this planet Key features of the earth that determine latitudinal and seasonal patterns of solar radiation 39 The Earth is a sphere 39 The Earth tilts on its axis 39 The Earth rotates around the sun These features result in systematic latitudinal and seasonal patterns in solar input to the earth That is more solar radiation strikes the Earth at some latitudes and at some times of the year compared to other latitudes and other times Further the pattern of annual seasonal variation in solar radiation depends on the latitude we will see transparencies from other textbooks in lecture Your lecture handout shows a graph of total solar radiation input by latitude for the entire year and for half the year spring equinox to fall equinox which is the northern hemisphere summer southern hemisphere winter From Pianka39s Chapter 3 Fig 31 This graph shows exactly how much solar radiation input measured in kcalcm2 falls by latitude this solar radiation input results in different temperatures which of course vary by season more below Concept of equinox and solstice What dates are the spring and fall equinoxes and the summer and winter solstices What is significant about an quotequinoxquot and a quotsolsticequot How do these times of year relate to solar radiation input on the Earth39s surface Molles Fig 23 shows the tilting of the planet by season and the angle at which solar rays enter the Earth39s atmosphere and strike the surface of the earth The angle at which the sun s quotraysquot strike the earth is very important for reasons too complicated to discuss here But you can get an intuitive feel for this angle this way When the sun is most directly quotoverheadquot the sun39s radiation strikes the Earth s surface at a 90 angle Because the earth is a sphere the sun s radiation strikes higher latitudes at increasingly shallow angles thus the energy from this quotbeamquot of light is spread over a wider area Convince yourself of this by taking a ashlight first pointing it straight down on the ground and then angling it away from you Do you see how the beam of light is concentrated into a smaller area and is brighter when you are pointing it straight down and whereas the circle of light on the ground gets larger and less bright at you put the ashlight at more of an angle 2008 Catherine A Toft EVE 101 Lecture 2 Page 5 Where on the planet latitude is the sun directly quotoverheadquot most direct entry of radiation into the atmosphere at the equinox and where at each solstice While the physics of energy heat and temperature are complex and out of the scope of this course we can easily enough see that the more total solar radiation input the higher the average temperature over a specified period of time for a given latitude You can find the table of annual January and July temperatures in Pianka s Ch 3 Table 31 Notice that the tropical latitudes receive the most total solar input This pattern results from the round shape of the earth in combination with the seasonal tilting of the earth s axis The low latitudes experience less change in the tilt toward the sun and solar radiation enters the atmosphere at closer to perpendicular 90 angle than at increasingly higher latitudes the angle depends on the season at all latitudes see Fig 23 page 15 of your text At higher latitudes the quotsummerquot season occurs when that hemisphere tilts toward the sun and the quotwinterquot season when that hemisphere tilts away from the sun The tilt of the earth determines the angle of entry of the solar rays the sun s rays enter the atmosphere at 90 over the two latitudes known as the quottropicsquot on each solistice On June 21 the quotsummerquot solstice of the northern hemisphere the sun is directly over the Tropic of Cancer or 30 N latitude on December 21 the quotwinterquot solstice of the northern hemisphere the sun is directly over the Tropic of Capricorn 30 S latitude this is the quotsummerquot solstice of the southern hemisphere Remember that the more perpendicular direct the entry the more radiant energy is absorbed by the earth s atmosphere The patterns of latitudinal solar input produce logical patterns in the mean annual temperature with latitude of course as well as the variation in temperature equally important This does NOT mean that the tropics 0 latitude are hotter In fact the world s highest temperatures occur around 30 latitudes as we ll see in a minute What this pattern does mean is that the tropics are consistently warm all year round on average in the high 7039s to low 80 s in degrees Fahrenheit We will see a graph in lecture on solar radiation input by month by latitude so that you can appreciate the latitudinal variation in solar radiation inut The latitudinal and seasonal variation in solar radiation input empowers the weather and climate systems of the planet As we shall see in the next section several physical factors combine to drive climatic variation but it all begins with seasonal and latitudinal inequities in energy input to the Earth s surface These quotimbalancesquot in energy input on the planet surface driVie the movement of water and atmospheric gases as these imbalances seek to come to equilibrium in the thin layer of gases constituting the Earth39s atmosphere At any given time the total energy budget of the Earth39s atmosphere is equilibrium total solar radiation input 2 output more or less However small variations occur during geological time such as might be driving the planet s ice ages and now we are experiencing quot global warmingquot as the Earth39s atmosphere seeks a new equilibrium as a result of the change in the composition of gases in the atmosphere In other words over short to medium time periods the average temperature of the planet s atmosphere overall is relatively unchanging particularly relative to the variation in temperature and energy input due to latitude and season 2008 Catherine A Toft EVE 101 Lecture 2 Page 6 C Global atmospheric circulation patterns The variation in solar radiation input energy and temperature thus drive the movement in atmospheric gases and their resulting ransport systems which we know as wind and precipitation water For example a volume air heated in one location has lower pressure than air in another location and this quotairquot moves quickly from higher to lower pressure regions which we experience as wind We will explore the global patterns in how the atmospheric gases move in this section The global atmospheric gases are in constant motion driven by a 39 a combination of latitudinal gradients in energy gain and loss tropical to arctic and 39 b the earth s rotation HOW 1 Pressure gradients Gradients in quotair pressurequot or the number of gas molecules in a particular volume of air are set up by temperature differentials heating the atmospheric gases at different latitudes Hot air rises which happens constantly in the tropics And these gases have to come down again because of the force of gravity If the Earth did not rotate daily on its axis the gas molecules in a parcel of quotairquot would rise at the equator 0 latitudeand fall at the poles 90 N and S 2 The Earth s Coriolis force However the earth does rotate daily and it is moreover a sphere which sets up another disequilibrium of forces on parcels of air traveling different distances in each 24 hour period This rotation produces forces known collectively as the Coriolis effect You don39t need to know anything more about the Corolis force but your book gives a brief explanation on page 16 Just keep in mind that a point on the Earth s surface travels much farther in one rotation than one near the poles and therefore much faster because it makes one compete rotation in the same amount of time Because of this Coriolis effect the parcel of air heated at the equator which rises therefore at 00 latitude returns to Earth at 30 and then rises again at 60 and comes back down at 90 So these circulation cells are set up by the high heat gain and rising air of the tropical latitudes and these cells are approximately 30 of latitude quotwidequot because of the Coriolis force Fig 24 Molles Vertical View of atmospheric circulation Your text Fig 24 and lecture handout page 1 give an idealistic schematic of the vertical circulation of the Earth39s atmosphere driven initially by the differential input of solar radiation uneven heating at the tropical latitudes Seasonally the latitude that receives the most solar radiation input changes from 30 N Tropic of Cancer at our summer solstice to 0 the Equator at the solar equinoxes spring and fall to 30 S Tropic of Capricorn at our winter solstice As a result the area of the quotintertropical convergencequot where the column of rising air occurs changes 2008 Catherine A Toft EVE 101 Lecture 2 Page 7 seasonally optional Smith Fig 47 The rising air of the intertropical convergence sets up two large vertical atmospheric circulation cells known as Hadley cells Mollies Fig 24 Smith Fig 47 To equalize pressure and because of the earth s gravity the atmospheric gases must circulate back down to the earth s surface which they do at about 30 on average producing a zone of high pressure and divergence of air at the Earth s surface Again to equalize pressure and for other reasons we see another zone of convergence at about 60 and a zone of high pressure and divergence at each pole While the Hadley cells are mostly as we see them in your text s and handouts idealistic picture the cells at higher latitudes are more irregular than you see in Fig 24 This vertical view is a quotcross sectionquot of the Earth39s atmosphere in altitude above the planet Next we consider what is happening on the surface of the Earth where we all live that is the horizontal circulation of the Earth s atmosphere otherwise known as quotwindquot Horizontal View of atmospheric circulation The horizontal motion of the atmospheric gasses also corresponds roughly to these 30 cells Molles Fig 25 page 17 lecture handout The Hadley cells the Coriolis force produce prevailing easterly Winds trade Winds between the intertropical convergence doldrums region of rising air and the falling air at around the 30 latitudes horse latitudes ie the tropics of cancer and capricorn Between the tropics 30 and 60 latitudes there are prevailing westerly Winds ie Davis and between the 60 latitudes and 90 latitudes there are prevailing easterly Winds Polar easterlies If there weren t mountains continents and oceans the earth s atmosphere would be set up in perfect circulation cells like Fig 24 and in your lecture handout as a result of the above three forces But there are mountains as well as ocean currents that affect surface temperature and that are set up by these same forces so the actual prevailing winds are really pretty messy See the transparency in lecture These circulation cells are crucial in determining the broad global ecological patterns caused by global variation in climate which in turn determines world patterns of vegetation plant life D Precipitation To understand climate we need to understand the relationship between moisture H20 in gas and liquid form temperature and the other atmospheric gases Again the physics is fairly simple and we don39t need to know much for EVE 101 The water molecule H20 can exist in liquid or gaseous forms depending on the temperature As a liquid this molecule is known as water and as a gas it is known as water vapor As ecologists we need to know two general principles 2008 Catherine A Toft EVE 101 Lecture 2 Page 8 1 The higher the temperature of a volume of air gases the more water vapor it can quotholdquot that is the warmer a parcel of air the more water vapor will be in it 2 quotPrecipitationquot occurs when this parcel of air cools and water vapor condenses to water or to ice if the temperature is cold enough which include hail and snow and falls to the ground Thus as warm air rises at the tropical latutides it also contains more water vapor As the air continues to rise it begins to cool by a process known as adiabatic cooling The of cial definition of the adiabatic process change in temperature sensible heat in a volume certain number of molecules of gases as that air is expanded or compressed without energy being lost or gained That is if you compress a volume of air the sensible heat increases and Vice versa when a volume of air expands sensible heat decreases and thus the air cools In the atmosphere a parcel of rising air is forced to expand without receiving or losing energy ie due to altitude and atmospheric pressure as the air moves away from the Earth s gravitational forces and it cools The opposite occurs in adiabatic warming in which an air volume returning to the earth s surfaces compresses as the gravitational force increases without any gain of energy and the temperature rises As the temperature of this parcel of air drops it can hold less moisture water vapor the water vapor in the air quotprecipitatesquot into water causing great amounts of precipitation mostly rain Tropical rainfall can be 2 4 meters per year Davis is 20quot or little over 05 meter 2008 Catherine A Toft EVE 101 Lecture 2 Page 9 II Consequences important for ecologists These fundamental physical properties of the Earth39s environment have important consequences for life on Earth in particular for the ecology of organisms That is we must understand how these physical properties of the Earth determine the distribution and abundance of organisms First we can view how these physical properties systematically vary across the planet s surface we call such patterns the climate Second we wish to know what patterns of living organisms correspond to global patterns in climate in particular the vegetation Plants are fundamental to all other organisms they fix energy and are at the base of many food chains and they are so predominant structurally that they often form the physical environment habitat for many other types of organisms The collection of dominant plants at a location is known as the quotvegetationquot and in turn the vegetation type is highly dependent on climate So we will cover these two topics in this section A Climate Climate refers to the annual profiles in temperature and precipitation in a given location above Climate determines a number of ecologically important patterns including 39 how landforms quotweatherquot erosion etc 39 how soils form 39 what types of plants can grow life forms 39 how plants interact with and affect feed back to physical environment 39 how animals and other heterotrophic organisms adapt to both the physical environment and the quothabitatquot formed by the plant life of that region 39 finally how water energy and nutrients quotcyclequot through the food web of that region For what we will emphasize in EVE 101 refer to lecture handouts Highlights of these figures are as follows refer to your text 1 The tropics 0 or quotlowquot latitudes low pressure intertropical convergence We see intense rainfall due to 39 a much input of solar energy heating the air and causing it to hold more water 39 b a powerful quotupdraftquot at equator that cools rising warm saturated air adiabatic cooling see above As the temperature of the air drops it can hold less moisture the water in the air precipitates causing great amounts of precipitation mostly rain Tropical rainfall can be 2 4 M per year Davis is 20quot or little over 05 M This rising air generates a low pressure area that causes the surface atmosphere to move from both north 2008 Catherine A Toft EVE 101 Lecture 2 Page 10 and south toward the zone of rising air an area known as the quottropical convergencequot This convergence zone varies in latittude according to season and its exact location is a bit unpredictable at any given time 2 The deserts at quotmidlatitudesquot high pressure This cell of air which rose at the tropical latitudes comes back down to the Earth39s surface at 30 latitude This air was cool and dry after it lost its moisture by adiabatic cooling It comes down and warms adiabatic warming from the increasing pressure due to gravity and this air takes up whatever water is available at the surface As a result these are the latitudes of the world s major deserts 3 The moist but cool higher latitudes There is rising air at 60 north generated by the interface between polar high barometic pressure and the lower pressure areas to the south This rising air causing recipitation to fall around this latitude during the year again as a result of adiabatic cooling Note a parcel of air thus rises at higher latitudes for a completely different reason than at the equator This air is forced upward by the Ferrel Cell colliding with the Polar Cell 4 The polar deserts Similarly to the 30 latitudes air is pushed down at 90 Again the air was dried by adiabatic cooling Now as it warms adiabatically it takes up moisture from the surrounding environment drying it So you see that the world s major climatic regions also correspond roughly to these atmospheric circulation cells This web site gives a summary for an entire course on the topic of this single lecture in EVE101 J JJ httpwww uwsn cu facultv ritter geoglOlbiomes tochtml B Effect of topography and continents Mountains and continents and ocean currents greatly alter these patterns of temperature precipitation and winds on the land surfaces of the Earth We can think of these modifications as local climate or even quotmicroclimatequot within a broader climatic region 1 Rainshadow effect of mountains Mountains that intercept prevailing winds cause air to rise and this air undergoes adiabatic cooling as it is forced up to higher altitudes and lower pressure The moving air drops all its moisture on the windward side of the mountain As the air moves down the other side of the mountain it undergoes adiabatic warming it expands and takes up moisture The lee sides of mountains are often dry deserts This is certainly true of our Sierra Nevada see Pianka Fig 36 2 Ocean currents Fig 35 p 51 The oceans are undergoing circulation patterns much like the atmosphere for the same reasons and these circulate water of different temperatures in relation to latitude The ocean circulation patterns like those of the atmosphere are affected by the topography of the ocean basins and the positions of the continents The ocean currents not only 2008 Catherine A Toft EVE 101 Lecture 2 Page 11 affect marine environments but also terrestrial continental and island environments Why Because air moving over the ocean surface is affected by the water temperature So warm ocean currents can go into high latitudes and moderate warm the terrestrial environments at that latitude such as the Gulf stream This is why Europe is so much warmer for the latitude than North America The opposite also occurs such as the cold currents off the coast of CA that bring cooled arctic water to CA coast causing San Francisco fog Mark Twain said that the coldest winter he ever spent was summer in San Francisco his novel Roughing It is highly enjoyable reading C World vegetation Lecture handout The vegetation of a region is the general and collective aspect of all the plant species found there What do we mean by aspect Most generally we get an impression of the size of the dominant plants in that region and all of the 111011 39 r 39 39 and 39 correlations with size In addition plants have life history adaptations related to climate and to their size In this section we ll explore why plant size responds so closely to climate In the meantime think of the common names that we use in every day English for the plants themselves such as tree shrub herb and for collections of plants such as forest woodland prairies savannahs See lecture handout p 5 6 for a glossary of all the terms that ecologists use to describe world vegetation This part of the course involves a lot of terminology and therefore some memorization but we need this vocabulary to understand patterns in the distribution and abundance of species worldwide which is of course the ultimate goal of ecology In this section we will explore why these patterns of world vegetation arise Because plants adapt to and are limited by their simple physical environment the vegetation of a region is highly predictable based solely on the annual and seasonal temperature and moisture profiles In fact a location s quotvegetationquot has little to do with the species of plants involved We see evolutionary convergence due to plant species adapting to the challenges in these physical environments Similarly animals and other heterotrophic organisms adapt to both the physical environment and the vegetation in a given region exhibiting evolutionary convergences of their own Determinants of primary productivity In a nutshell climate determines a plant39s potential rate of evapotranspiration which in turn regulates the plants overall rate of photosynthesis and its ability to fix energy from the sun The rate at which a plant can fix energy from the sun determines both the size of the plant that is possible under a given climatic regime and also collectively adding over all plants at that locationthe total primary productivity of that region See Molles Ch 18 pp 413 5 424 6 and review photosynthesis in Ch 6 pp 134 8 We won t go into a precise definition of evapotranspiration see your text s glossary p 571 evapotranspiration is the sum of the loss of moisture by evaporation from land and water surfaces and by transpiration from plants A plant just like an animal has to quotbreathequot and 2008 Catherine A Toft EVE 101 Lecture 2 Page 12 exchange gases for respiration O2 gtC02 and for photosynthesis CO2 gt02 A plant exchanges gases through its stomates stomata which are openings to stomatal chambers that function just like lungs in the next lecture we will learn in more detail how this process works All terrestrial organisms lose water when they exchange gases and plants lose water through their stomata when the stoma is open for gas exchange transpiration Plants can conduct photosynthesis only when their stomata are open to exchange gases but if too much water is lost then the plants must close their stomata to stop evaporation of water by that route Because external temperature and moisture determine the rate of evaporative water loss these physical factors highly influence how much photosynthesis a plant can accomplish in a given environment and climate and hence how much primary productivity The primary productivity of a region 1 determines the base of food webs and energy pyramids in a given ecosystem and 2 the physical structure of the plant species there that is the physiognomy of the vegetation Thus the primary productivity of the region affects all species of organisms at that location and the characteristics of the total ecosystem at that location The general vegetation of a region typified by its physiognomy combined with the food webs dependent upon it is termed a biome A biome is typically defined by the dominant vegetation but ecologists are familiar with the characteristics of the other organisms typically found in that biome Refer to your lecture handout for a glossary of important terms See the appendix for a primer of evapotranspiration The more technical information in this appendix is not required but may be helpful for those of you wanting a deeper understanding of this topic This web site gives a full survey of the world s biomes You can google world biomes and get some good pages to review including wwwworldbiomescom The simple effects of climate on the physiognomy of vegetation is remarkable Regardless of the exact species or even family of plants at a location the climate will determine the physical aspects of all the species of plants there In other words the evolutionary relationships of plants is not as important at the ecological and physiological relationships of that plant species with its environment and plant species at different locations with the same climate undergo evolutionary convergence to adapt to that physical environment For example a grassland is a biome such as the great prairies of the center of North America including the eastern quottall grass prairiequot and the western quotshort grass prairiequot see Molles Ch 2 32 34 and Fig 225 Large grazing mammals are typical of grasslands which are in turn associated with pack hunting predators The grasslands and savannas a grassland with scattered trees of Africa show considerable evolutionary convergence with those in North America regardless of the actual species involved Thus North America had bison prong horned antelope 2008 Catherine A Toft EVE 101 Lecture 2 Page 13 and wolves whereas Africa has or had gnus wildebeest and numerous antelope lions and jackals On both continents grasslands are typical of regions with moderate temperatures and relatively low rainfall Your book in Ch 2 covers a sampling of the world s biomes including a discussion of climate vegetation and characteristic animals The textbook by Smith has a map of the world s biomes on the inside cover Classi cation of world vegetation biomes Because the vegetation type is so remarkably predictable by the region s climate ecologists have originated numerous schemes for predicting patterns of the world s vegetation based on simple information on a region s climate In particular two plant ecologists have created enduring classification schemes that relate vegetation type physiognomy with the climate of the region moisture and temperature or related parameters the schemes by RH Whittaker Smith Fig 423 p 58 and L R Holdridge Smith Fig 430 p 59 Your text does not have a full chart of the world biomes on any one graph rather you will see different biomes You can google up the figures to view on the web Type world biomes whittaker or world biomes holdridge under the google image search You can also see the full color versions in the lecture powerpoint For the rest of the lecture we will review these two classical schemes We will return to this quotbig picturequot view at the end of the quarter once we have learned many underlying ecological principles that govern the distribution and abundance of organisms Whittaker s scheme is based only on the physical factors average annual precipitation and temperature Side note Robert Whittaker was a well known plant ecologist who was highly influential in the field of community ecology among others His book Communities andEcosystems is a classic text Tragically he died at a young age no doubt depriving the field of ecology of further contributions Holdridge s scheme is much the same as Whittaker s except that it makes explicit the relationship between these physical factors and latitude altitude and it incorporates that key feature plant ecophysiology quotevapotranspirationquot Notice that the physical environment by latitude and altitude varies in similar ways and so we see parallel changes in plant communities as one travels north or south or up and down a mountain Go over the two schemes now and become familiar with the names of the major physiognomic vegetation types These major vegetation types are of utmost importance in providing quothabitatquot for animals and other heterotrophs During the quarter we ll learn about the many other biological factors that are associated with these vegetation types As a working ecologist you will continually return to these major classification schemes for vegetation types and biomes in just about every endeavor an ecologist undertakes 2008 Catherine A Toft EVE 101 Lecture 2 Page 14 Appendix Primer of evapotranspiration from Smith 1996 Gates 1980 Evapotranspiration is the movement of water from the soil into the atmosphere as water vapor as a result of evaporation of water from the soil surface and from the gas exchange surfaces of plants as obligatory evaporative water loss It is a complicated concept it combines the issue of water available to plants in the soil environment and climate with the biological activity of plants as they attempt to conduct photosynthesis at a maximum rate for that climate The rate of evapotranspiration is intimately related to the rate of photosynthesis for several reasons The rate of photosynthesis is proportional to the rate of C02 uptake from the atmosphere gas exchange source of carbon and to the rate of carbon fixation as complex carbohydrate molecules output of carbon as stored energy also known as primary productivity It is dependent on temperature as a physiological process enzymes and reactions work faster or slower depending on temperature In addition photosynthesis is also dependent on moisture available to plants because this moisture potentially limits gas exchange Plants detecting a net loss of water will begin the process of closing their stomates and thus will experience lower than maximum possible gas exchange for that temperature Transpiration thus is an index of photosynthetic rate if soil moisture is not limiting to plants transpiration can occur at a maximum with no net water loss from the plant thus allowing a maximum rate of photosynthesis However once water becomes limiting transpiration also includes the net loss of water to the environment and thereby re ecting a decreasing rate of photosynthesis The water budget of a plant is a function both directly and indirectly of precipitation temperature and water vapor in the air humidity However virtually all of the water available for plants to replace water lost by transpiration is held in the soil where it is taken up by roots Soil moisture in turn is determined by the climatethe armual pattern of precipitation which recharges soil moisture relative to the location s temperature which determines evaporation from the soil surface or loss to soil moisture To make things more complex climate also determines soil development and soil type which in turn affects the soil s capacity for storing moisture Potential evapotranspiration is an index of water availability for the biological activity of plants and measures the potential for plants to carry on photosynthesis at a maximum rate for that climate Potential evapotranspiration is a hypothetical index and not directly measurable it is a function of biologically positive heat balance or biotemperature Potential evapotranspiration is the amount of water that would be transpired under constantly optimal conditions of soil moisture and plant cover This index is calculated by multiplying mean armual temperature by an experimentally derived constant 5993 The potential evapotranspiration ratio in the Holdridge scheme is the mean armual potential evapotranspiration PET mm divided by the average total precipitation mm This ratio becomes an index of biological humidity if the ratio is 10 then armual precipitation exactly replaces water potentially lost by evapotranspiration If the ratio is less than 1 then there is an excess of water available to replace all water lost by transpiration at the average temperature of that climate water is therefore not limiting to the rate of photosynthesis only temperature is However as the ratio gets greater than its minimum value of 0125 and still below 10 water may be limiting for part of the year depending on the monthly distribution of the total armual precipitation If the ratio is greater than 10 the total armual precipitation cannot recharge soil moisture sufficiently to cover water loss by evaporation over the entire year so that an evapotranspiration deficit is assured in some major proportion of the year The humidity provinces of the Holdridge scheme are categorized as humid above 1 and subhumid and ari below 1 2008 Catherine A Toft EVE 101 Lecture 2 Page 15 Note that the potential evapotranspiration axis Smith s Figure 430 of the Holdridge scheme is mislabeled and is inconsistent with the text s explanation on page 58 The axis should read potential evapotranspiration ratio other texts use the word relation which is potential evapotranspiration rate PET mm divided by the total annual precipitation The triangular shape of the Holdridge scheme results from the perpendicular axes sharing common variables The Yaxis is straightforward it is only the mean armual temperature The Xaxis is humidity which combines temperature and precipitation The independent precipitation axis then runs diagonally to these two axes The Whittaker scheme Figure 428 is much simpler to understand using the independent and easily measured variables of mean armual temperature and total annual precipitation but it is less explanatory in omitting the physiological mechanism Both schemes are graphically triangular because colder air holds less water vapor which means there is decreasing total armual precipitation with decreasing mean annual temperature Actual evapotranspiration is tightly correlated with total primary productivity and these quantities are in turn characteristic of physiognomic vegetation types Fig 152 in Molles Broadly the amount of primary productivity possible will be re ected in the size of the largest plants Thus forests require more moisture than woodlands than scrub than savarmas than grasslands than desert vegetation for example The seasonal pattem of precipitation also matters this information is more evident in Whittaker s labeling of biomes than in Holdridge s terminology 2008 Catherine A Toft EVEl 01 Lecture 6 Part II Page 1 Lecture 6 Singlespecies population growth Part II Readings Molles Chapters 1011 Part I I Introduction elements of population growth 11 Types of population growth 0 A Exponential geometric Density independent PG 0 B Logistic Density dependent PG 0 C Examples of exponential and logistic population growth 0 D Mechanisms of density dependence 111 Simple models of population growth 0 A Background 0 B Exponential C Logistic PG and density dependence 0 D Allee effect reverse density dependence Part 11 IV Demography 0 A Background 0 B Age structured population growth and life tables 0 C Estimating population growth rates V Reproductive strategies revised January 18 2008 Molles 4 h edition pages 2008 Catherine A Toft EVE101 Lecture 6 Part II Page 2 Lecture 6 Single species population growth Part 11 IV Demography A Background lecture handout Molles Ch 10 Notice that the above models are very descriptive We don39t bother to incorporate any mechanisms that determine how individuals are born grow reproduce and die at best we separate birth rates from death rates but we don39t do much with this one biological detail All of the parameters of the model are descriptive ie without speci c mechanims invoked or implied When biologists go out to estimate r then they can39t do that directly because r is an abstract concept although it is a real one Rather biologists find individuals animals or plants mark them follow them count up the numbers of babies or seeds that they have and record when they die This is the study of demography The more we know about the demography of a population the better an estimate of r we can get The intrinsic rate of increase r is an abstract concept in that it is a composite of many different J J 39 processes eg age specific births and deaths reduced to an instant of time In fact individuals in a population vary and all of the demographic processes take finite amounts of time The intrinsic rate of increase is very useful both as a simple description of population growth and for predicting future population sizes However an ecologist needs to measure much 39 detail about a population in order to get an accurate estimate of r B Age Structure Ch 104 Figs 1019 21 1124 lecture handout 1 Age distribution The simplest population models have another assumption then that all individuals are the same That is a serious error of omission In this unit we ll look at age structured population growth as described by life tables the basis for the science of demography The most fundamental way that individuals in a population differ with respect to characteristics determining population growth is their age When individuals are born they do not instantly begin to give birth to new individuals or instantly die at a constant average rate as stated in the simple models above Instead it takes a while for individuals to grow to sexual maturity In other words individuals do not give birth at the same rate throughout their lifetimes Similarly individuals at different ages have different risks of death for example young individuals and older individuals are frequently more likely to die than individuals of adult age So you see not only an age specific source of variation you see that age specific birth and death rates can show interesting relationships 2008 Catherine A Toft EVE101 Lecture 6 Part II Page 3 These distributions plot the number or percentage of individuals in a population in each age category You collect data for plotting these distributions in two ways text p 240 39 Cohort horizontal life table You start with a quotcohortquot a group of individuals all of the same age You follow a group of individuals all born in the same census interval throughout their lifetimes At each age census interval typically one year you count the individuals for the simple age distribution and in doing so you find out out many have died since the last census more below The accuracy of this kind of life table depends on your ability to follow individuals throughout their lives without losing them 39 Static vertical life table You record all the individuals in a population of all ages in a single census interval The accuracy of this type of table depends on your ability to estimate the age of the individuals in the population to at least the precision of the during of one census interval ie one year Often the age distribution is plotted so that males and females are kept separate and are juxtaposed as mirror images to one another So the age distribution looks like a quotChristmas treequot cartoon Fig 1124 In this case age or census intervals is plotted on the vertical Y axis Other types of plots are more conventional with age or census interval on the X axis and frequency on the Y axis Figs 1019 21 Usually proportions frequency of the population in each age class is plotted and not the raw number of indivdiduals You can tell a lot about population growth as we will see just by looking at one for example you can distinguish a rapidly increasing from a declining population When proportionately more individuals are in the younger age classes we infer that this population is growing at a faster rate than another population The reason has to do with proportionately more individuals moving into the reproductive age classes to give birth in future time steps Fig 1125 p 274 2 Agespecific survivorship lx Ch 103 Figs 1014 19 lecture handout Survivorship 1 is computed as the number of individuals alive in age interval X the number of individuals born ie the number at the start of the first census age 0 so that X 0 This is formally the proportion of individuals in that cohort surviving to age x ge specific XN0 or the number of individuals surviving to age x divided by the number survivorship lX f individuals born in that cohort The notation classically used for age specific survivorship is lx The age or census interval of interest is usually noted as X above time more generally is noted as t However different notation schemes vary Age specific survivorship is plotted as quotsurvivorship curvesquot with the proportion surviving to age x plotted typically on a logarithmic scale against age From plots of real organisms different patterns of survivorship can be seen These are summarized as Type I II III survivorship curves Fig 1018 and they tell us about the life history of an organism in particular its 2008 Catherine A Toft EVE101 Lecture 6 Part II Page 4 evolutionary strategy Fig 1018 lecture handout 39 Type I eg humans After perhaps a short period of high infant mortality mortality is very low for a long time Individuals then die at a faster rate as they approach maximum longevity Type II eg birds and lizards Each age class has the same probability of making it to the next age class that is risk of mortality is constant throughout the individual39s lifetime Type III eg insects and many plants early life stages have a very high risk of mortality with most of the individuals born dying before reaching sexual maturity There are two versions of this type of survivorship curve 1 all individuals in the population die in the first or second census interval as in annual plants 2 a few individuals make it to sexual maturity and then their risk of mortality is very low with some individuals living to extreme old age as in many trees Find examples from the book and from transparencies 3 Agespecific fecundity mx Table 101 and 102 lecture handout As we discussed above most species have some prolonged period after birth in which individuals grow until they reach sexual maturity Then after sexual maturity is reached individuals in a population might vary in the number of offspring they produce at different ages In most species older individuals eventually slow down or completely stop reproduction before the maximum longevity is reached We call the number of offspring that an individual has or potentially can have fecundity In formal terms we record agespecific fecundity by examining the average number of offspring produced by an individual at age X age specific fecundity mx average number of offspring produced by an individual of age x Because most species have the usual two sexes and only females give birth age specific fecundity is a female trait The number of offspring or eggs or seeds per female is mx In monoecious organisms often only the females are recorded in a census and then a 5050 sex ratio is assumed usually a safe bet However you keep track of the data is fine as long as you are consistent keeping track of demographic data is simple bookkeeping You can lump males and females and divide mX by two or you can just keep track of females Fecundity is typically highest at either the age of first reproduction or the year after the age of first reproduction and it goes down steadily from there There are two general patterns of age specific reproduction we will cover California examples in section I semelparous annual plants salmon one reproductive event per lifetime 2008 Catherine A Toft EVE101 Lecture 6 Part II Page 5 39 iteroparous perennial plants most animals multiple reproductive events per lifetime after some age of first reproduction C Estimating population growth rates 1 NET REPRODUCTIVE RATE is the rate at which the population is growing First we will derive it and then relate it to simple models we first considered Molles Ch 105 R 21me net reproductive rate R0 the average number of offspring produced per individual per generation You just take a population and add up quotlxmxquot which is the probability an individual will survive to age x and multiply that by the fecundity at age X This quantity will be the probable number of offspring produced by an individual of age x can you see how this quotlxmxquot is different from quotmxquot The latter quotmxquot is the average number of offspring produced by an indivdual of age x quot1mequot is the probable number of offspring because the average number of offspring is weighted by the probability that an individual will survive to age x In other words we don39t know for certain whether any given individual will survive to age x so we have to discount the fecundity of individuals at age x by the proportion of individuals that might die before reaching that age See how the two graphs quotcombinequot to form lxmx function bottom graph lecture handout The area under the curve is the net reproductive rate R0 which can also be thought of as the number of offspring produced by an average individual in its lifetime Two important things to learn from the lxmX schedules 39 1 Notice that the highest contribution to R0 is often right after the age of first reproduction That39s when females usually have both the highest fecundity and the highest probability of living at least that long because they are at the youngest age they can reproduce and some mortality is expected as they get older 39 2 Because you are using the probability of survival the whole thing is scaled so that exact replacement is 1 That is you replace yourself with exactly one individual and because that is true of everybody in the population then the population size is constant through time it is neither increasing nor decreasing Births and deaths are exactly quotbalancedquot on average an individual produces one offspring during its lifetime generation exact replacement 2008 Catherine A Toft EVEl 01 Lecture 6 Part II Page 6 2 Biotic potential the instantaneous percapita population growth rate How does R0 relate to little r Remember the rum of the simple population model This is also a rate of net births and deaths These two rates are related but have different units lnR r T 0 where T 1s the mean generatlon t1me See proof on web httptrc ucdavis f 101 J u r0nrf htm R0 is the finite rate of increase the number of new individuals produced by one individual during its generation It is equivalent to the geometric or net rate of increase A for species with discrete non overlapping generations where A NMNt See Molles pp 245 8 We can convert that to the instantaneous rate of increase r by taking the logarithm and dividing by generation time We won39t go into how to compute mean generation time but check out Table 102 on your own with the example of the life table the mud turtle One way to think of mean generation time as the age class that on average makes the largest contribution to the production of offspring Thus generation time is closer to the age of first reproduction than it is to the greatest age reached by individuals in that cohort This relationship of r and R0 has important implications Notice that r is related to the logarithm of R0 Remember that r represents a compounding of population size when populations grow exponentially What happens when you take the logarithm of a number Importantly the variation in that number is less than that on an arithmetic scale However r is related to T without any logarithmic transformation In other words r is much more sensitive to changes in T the mean generation time than is it to changes in the average number of offspring produced per generation To slow the per capita rate of growth of the human population for example people could have a large impact on r by delaying marriage and starting their families later Remember that T mean generation time is strongly related to the age of first reproduction rather than the maximum longevity of individuals So if people delayed having families r would get smaller faster than if they simply reduced the number of children that they had but still started their families at a young age In most cultures education and increasing the quality of life generally results in both the delay of marriage and the reduction of family size Clearly education quality of life and the ability to make choices about reproduction have extremely important effects on the rate of human population growth While increasing the quality of life increases the amount of resources used per individual this effect of resource consumption can be compensated by a correlated decrease in the per capita population growth rate So education is a good thing To limit your impact on the planet then you can choose to have fewer children later in life as well as making lower impact choices in your lifestyle that use resources as efficiently as possible 2008 Catherine A Toft EVEl 01 Lecture 6 Part II Page 7 V Reproductive strategies Lecture handou Chap 12 especially Ch 123 We might now consider how the traits that contribute to population growth evolve The environment in which an organism is found determines how organisms maximize their individual fitness What we will find is that there are variations on how to maximize the number of offspring you leave to future generations Here we can see the links between ecology population growth and evolution fitness of individuals and populations each area focusses on how organisms survive and reproduce a quotstrategyquot His a conceivable evolutionary response to a set of ecological conditions Because of the principle of allocation organisms cannot do everything equally well they must invest in some types of strategies at the expense of others The environment sets the stage for which strategy to use where Organisms evolve suites of traits that recognize tradeoffs in how organisms allocate energy and time to reproduction and survival An extremely important tradeoff greater investment in reproduction means lower investment in survival and vice versa We can expand on these ideas by introducing the concept of life history life history Hbirthgrowthsexual maturityreproductiondeath Where we putquot quot the organism is faced with the challenge of surviving to the next life history stage in particular the organism must survive to reproduce and also survive between reproductive events if there are more than one The individuals fitness is determined by its ability to survive and to reproduce Natural selection will act on the different life history stages to produce a life history that maximizes fitness in a given environment Because we are now explicitly talking about survival and reproduction we are talking about the elements of population growth Thus population behaviors will be closely correlated with life history patterns Go to lecture handout These are evolutionary generalizations about factors selecting for life history traits and determining reproductive strategies and population growth They are labeled quotrselectionquot and quotKselectionquot from the logistic equation These suites of characteristics are what tend to arise under density independence conditions rmX dominates low N versus density dependence conditions 1 N K dominates N is near K We ask what are the characteristics of the environment What then would be the evolutionary response in how organisms allocate energy and time to different parts of the life history Importantly we can recognize two ends of a continuum of environmental settings in which life 2008 Catherine A Toft EVE101 Lecture 6 Part II Page 8 histories can evolve 39 Environment in which rselection occurs ie low population densities What are the environmental conditions that would ensure that populations are at low density much of the time These conditions include unpredictable and harsh environments and frequently disturbed environments that result in catastrophic mortality Type III survivorship and density independent mortality Organisms should respond by investing little in quotselfquot ie survival and as much as possible in reproduction and dispersal Environment in which Kselection occurs ie high population densities We would expect population densities to become high in benign and predictable environments Under these conditions density dependent effects are strong Organisms should respond by investing in quotselfquot and survival and less in reproduction what they invest in reproduction should be similarly invested more in parental care and survival of young than in sheer numbers of young The table in your lecture handout details suites of traits that we might expect to be associated by natural selection why How does the principle of allocation apply here Do you agree think of your favorite type of organism that these traits should always be associated We will cover these ideas in more detail in section See Fig 1011 in Molles which shows the common sense observation that body size and generation time are correlated for all kinds of living organisms This graph gives us a specific quantitative scale for this relationship Is it valid to say that larger organisms are more likely to be K selected than smaller ones Maybe but this type of comparison is too broad to be useful It39s better to compare species or populations with a close common ancestor to get the clearest idea of how a reproductive strategy is a response to ecological conditions Alternative frameworks for understanding life histories Molles s Ch 12 is an excellent introduction to key concepts in understanding the evolution of life histories if you are going on in ecology you should read this chapter carefully Molles discusses other schemes for organizing what we know about life histories adapted from Winemiller and Rose s study of fishes and Grime s study of plants see how the unique biology of each taxon provides a more specific framework for life histories within that taxon All of these schemes Winemiller amp Rose Grime Pianka Figs 1020 22 are based upon the universal existence trade offs and therefore the principle of allocation p 280 The axes in the other two schemes Figs 1221 and 1222 indicate the key trade offs for that taxon Why would I 1 competitive ability ability to tolerate stress and ability to disturbance represent life history trade offs List the life history traits that might be associated with these axes in Grime s scheme I 2 juvenile survival fecundity and age of first reproduction require trade offs These axes of Winemiller amp Rose s scheme are explicitly life history traits Why as in Pianka s scheme do these traits require trade offs 2008 Catherine A Toft EVEl 01 Lecture 6 Part II Page 9 2008 Catherine A Toft EVE 101W08 Midterm 1 Questions EVE 101 Midterm 1 questions Winter 08 Topics covered Lectures notes and handouts through Thurs Jan 24 and assigned readings in the text Note The actual questions may differ slightly in wording or structure if we think a question was worded poorly or is too long but otherwise the exam questions will be as they are here Point values will change with any given exam Approximately 1012 questions will be on the actual exam Notice that there is often a group of possible questions van39ations on a particular topic you can expect only one question from this group on the exam Study hints Individual questions may have study hints next to them in brackets These study hints will not be reproduced on the test Here are some general study hints for all the questions When an example is called for in a question you should provide a real example such as provided in lecture section or the book You can draw on your own experience but be sure that you are correct and that your example is scientifically documented Something that you saw on Nova may or may not be backed by a Iigorous scientific study Hypothetical examples will receive no credit Also be sure not to substitute an example for an explanation if the questions calls for an explanation Remember to label axes on all graphs Not labelling axes is one of the biggest sources of lost points and it s bad form scientifically speaking In practice label the graphs axes X and Yaxis first always and then draw in the relationship between the two van39ables Keep in mind that generally the Xaxis is the independent variable and the Yaxis is the dependent van39able That is we wish to understand how one variable depends on the other Review the quotSummary Conceptsquot section at the end of each chapter that we cover from your textbook These chapter summan39es are excellent at condensing important concepts in a few words H A general definition of evolution could be genetic change in a population of organisms through time Give a more specific explanation of evolution by natural selection In your answer define adaptation The most complete and precise answers will receive the highest score 2 A Define ecotype B List and explain three conditions ecological or evolutionary required for ecotypic differentiation of populations within a species by the process of natural selection 3 A Provide an example of an ecotype B Explain how this example fits the definition of ecotype as a locally adapted population The most complete answers will receive the highest score 5 Explain how climate can cause ecotypic differentiation and evolution Choose one example and discuss how you know these are different ecotypes In your answer be sure to define ecotype Study hint This question asks you to integrate maten39al from three different lecture topics and the text Think about morphological and physiological adaptations and how to distinguish evolutionphenotypic plasticity The Yarrow example on p 1878 Fig 84 is a good way to think about this question and it s about California too U List five factors that might determine the distribution and abundance of an organism and descn39be how you as a budding ecologist would test the importance of one of those factors Study hint this is a thought question not specifically covered in any one lecture but you should have enough information to pull together an answer to this question 1 EVE 101W08 9 gt1 00 H O H H H N H W H 4 H LII H C Midterm 1 Questions Your text Molles states that quotMuch of the earth s climatic variation is caused by uneven heating of its surface by the sun quot Amplify this statement by explaining A What properties of the planet Earth cause this uneven heating B What are the atmospheric and climatic consequences of this uneven heating Be general but complete Why do the tropical latitudes receive the greatest annual precipitation Be as complete and as concise as possible Study hint include a description of atmospheric circulation latitudinal variation in solar radiation and the relationship between temperature and moisture in the atmosphere all of which you need to explain this pattem Why are the world s greatest deserts found roughly around 30 latitude Be complete Same study hint as 4 You should mention all major global pattems in temperature solar radiation and atmospheric circulation required to produce this pattem A Draw a WalterLeith climate diagram Fig 26 etc in Molles and B explain how this particular type of diagram allows us to compare climates at different locations and the conditions that affect photosynthesis by plants Study hint how are the axes aligned Why P 17 A WalterLeith climate diagram uses both temperature and precipitation axes on one graph and aligns them so that 10 C and 20 mm precipitation coincide on the Yaxis Explain A the biophysical significance of these two values and B the ecophysiological consequences for plants Study hint same as previous question and covered in the lecture on ecophysiology A Define a Mediterranean climate such as we have in California What global conditions produce ie lead to this climate pattem B How do the various regional climates of California vary within the general Mediterranean pattem OR A Use a WalterLeith climate diagram to illustrate a Mediterranean climate pattern B On your graph identify the area if any of potential evapotranspiration deficit C What effect does an evapotranspiration deficit have on plants Describe Holdridge s OR Whittaker s classification of biomes How does such a scheme promote our understanding of the patterns of world vegetation Choose any two biomes from Chapter 2 and contrast their climates and vegetation types A Sketch out an approximate climate diagram for those two biomes or describe their climates in words B Describe the physiognomic vegetation type characteristic of each biome and give a brief explanation for why that vegetation type occurs there As an ecologist you should be able to explain why trees are the dominant physiognomic form of vegetation in one location and grasslands in another In your answer define physiognomy What are the primary factors that allow you to predict the vegetation at a given location Why do these factors such a strong in uence on plants You can use trees and grasses or any other example A What is primary productivity B What factors are the major determinants of primary productivity as evidenced by global pattems in primary productivity A Give a general explanation of evapotranspiration B How is climate related to actual and potential evapotranspiration in plants C Explain why terrestrial biomes are highly correlated 2 EVE 1 17 H 00 H N N N LII 01W08 Midterm 1 Questions with a region s climate actual evapotranspiration rate and primary productivity Using a graph explain how physiological performance and the concept of performance optima under different environmental conditions are related to an organism s individual fitness A Illustrate the concept of primary productivity using a physiological performance graph Important Be specific B Explain how the physical conditions that you have chosen for your determine the plant s physiological response Study hint your performance graph will need to designate net photosynthetic rate somehow How would you do that u I I u 439 A Distinguish 39 y t quot from J B Give an example of each process but don t substitute the example for answering part A C How might acclimation itself be adaptive you should frame your answer in precise evolutionary terminology a variation on this question might give you a choice between the big saltbrush study or the rainbow troutbass study Dr Pearcy s study on the ecophysiological performance of big saltbush Atriplex lentiformis from two populations desert and coast of California illustrates both the concepts of adaptation and acclimation Describe his experiments and explain how this example shows 1 adaptation and ecotypic differentiation andor 2 acclimation Be complete and include performance curves in your answer be sure to label axes Study hint Dr Pearcy s experiments are explained in detail on pp 8990 Fig 410 411 Explain how the experiment on rainbow trout and small mouth bass illustrates the difference between 39 y 39 quot and 1 39 39 39 In your answer be specific and complete include A the experimental design B an explanation of physiological performance and C a carefully worded distinction between adaptation and acclimation Clearly distinguish the concepts of ectotherm endotherm poikilotherm and homeotherm How do these concepts relate to whether an organism is a thermal conformer or thermal regulator Use examples if you like but don t substitute an example for an explanation What are the fundamental problems facing terrestrial organisms in maintaining a proper water balance In particular explain Why at least some water loss to the environment is unavoidable Consider both animals and plants in your answer A A water vapor pressure deficit in a terrestrial environment is comparable to what kind of osmotic concentration gradient in an aquatic environment B Discuss how either condition affects an organism s ability to maintain homeostasis C Discuss how an organism might respond Study hint In your answer define and distinguish hyperosmotic and hypoosmotic regulator andor environment That is what kind of regulator is this question asking you about Define homeostasis as part of your answer Choose one of the examples from your book under Water Conservation by Plants and Animals pp 118125 examples include camel saguaro cactus cicada or scorpion or lecture kangaroo rat and explain how these desert organisms conserve water in an extremely dry and hot environment EVE 101W08 Midterm 1 Questions 26 Brie y explain the difference between C3 C4 and CAM plants and explain which are most likely to occur in desert hot dry grasslands and forest understory environments Be sure to discuss reasons for your answer N l Describe ways that ectothermic organisms can regulate body temperature and or water loss using behavioral physiological and morphological means Choose either an animal or plant example for your discussion Study hint but don t just substitute the example for your explanation N 00 A Explain how the desert iguana can control its body temperature even how this lizard is an ectotherm B Now explain Why a desert iguana would go to this trouble to regulate its body temperature in an ecological and evolutionary context N D A Define the principle of allocation and the related concept of quottradeoffsquot B Describe an example of the principle of allocation from the lecture notes section handout or text to illustrate the ecological or evolutionary significance of this principle 20 O Discuss the concept of optimality in ecological models such as in optimal foraging and optimal territory size models What are the possible objections that an ecologist might have to the concept of optimality How can you make the concept of optimum a useful and rigorous scientific concept Note in the following questions be sure you know the difference between an assumption and a prediction You will not get credit for giving an assumption when we ask for a prediction and vice versa If you re not sure which is which ASK during the preexam office hours For the following questions consider this simple optimal foraging model 29 What does the optimal foraging model predict in the following situations about the food types that an animal includes in its diet 1 If abundance of all food items increases how does this affect the range of items included in the diet 2 How do the characteristics of a food typethe relative abundance of that item p or its quality eitdetermine whether a food type is chosen once it is encountered Justify your answer Study hint there is no single correct answer to this question 30 Give the two basic predictions that arise immediately from simple optimal foraging theory about how animals forage Study hint what are the two predictions from the first two problems on your optimal foraging theory handout EVE 101W08 31 32 33 34 35 36 37 38 Midterm 1 Questions A How does the number of food types included in the diet change when the overall food abundance increases B Which variable in the model re ects the change in overall food abundance Study hint the variables in the model are e t p TS CS C Speculate on why a change in this variable produces a change in the predicted number offood types in included in the diet List and explain x assumptions x is usually 34 out of 7 possible of the simple model of how animals forage optimally Study hint an assumption is either an a priori fundamental property of the pattern or process under study OR a simplification in the spirit of scientific parsimony A What exactly is the optimization goal of the simple foraging model we covered in class B Is this the only possible goal that foragers might have List at least three other goals that might be incorporated into a different or more advanced model of optimal foraging Study hint The optimization goal of our model in class was to maximize energy yield per unit time A What kind of search does the hypothetical animal use in the simplest optimal foraging model B Why is this or any kind of search process specified C Is this type of searching realistic If yes give examples of types of foragers that use this search If not then explain how real foragers deviate from this pattem OR A What does it mean to assume that an animal searches randomly Study hint how does random search determine which types of food are encountered and how often A Give an example of an experimental test of optimal foraging theory B Explain the predictions of OFT to be tested and how the experiment tests those predictions C How did the forager perform relative to the predictions from the simple optimal foraging model What explanation do you have for deviations if any from the predictions Explain one of Werner Hall and Mittlebach s experiments on bluegill sunfish that tested optimal foraging theory Include A how the experiment or data collection was set up and what predictions of OFT it tested and B how predicted diets and observed diets compared How well did bluegill sunfish fit the predictions of the simple optimal foraging model C What is your conclusion about the ability of optimal foraging theory to predict actual diet Study hint one experiment is explained in your book on p 149150 List and explain 3 assumptions of the simple model discussed in class of how animals forage optimally Discuss two cases where one or more of these assumptions may be violated using evidence from class or your text In testing a simplifying model such as the optimal foraging model scientists hope to leam more about how real animals forage especially when the model does not correctly predict what real animals do Explain how the simplest optimal foraging model fails to predict the behavior of real foragers and what that tells us about their foraging behavior A How well do the predictions of the simple optimal foraging model match observations from nature or results of experiments B What do the deviations from the simple model if any tell you about real foragers OR if foragers fit the predications of the model well how did using the model teach us something about nature that we couldn t simply have observed directly ie without using a model EVE 101W08 39 40 41 42 43 OR 45 46 47 48 Midterm 1 Questions Contrast the two foraging modes sitandWait vs active searcher A What are the relative costs and benefits to each mode B Do you expect that the two modes will provide equal net benefits Study hint your answer could contrast time scales ie the long run ie the individual s lifetime versus the short run ie on a given day or in a given season You could talk about the study of the Kalahari lizards Two species of lizard in the genus Eremias with different foraging modes were studied in the Kalahari desert by Nagy Huey and Bennett A Explain the results of their study compare the two foraging modes Which foraging mode yielded the higher profit B If one foraging mode is more profitable than the other then can you explain how the lower profit foraging mode could evolve Give at least two reasons that could account for the existence ie evolution of both foraging modes A Explain Gary Belovsky s study that tested hypotheses on optimal diet of moose B What were the foraging goals of moose in his model and how did that make his model different from the simple model that we covered in class C Among other things he tried to predict which members of the moose population would be energy maximizers and which foraging time minimizers What were his predictions and were they correct Why or why not Be concise but complete be sure to define your terms A How is the body size of an animal related to the size of its home range B List 3 factors that seem to determine the exact form of this relationship C Why Give a reason for the observed patterns A What is the difference between a home range and a territory For each explain brie y what factors that determine the size of a B home range and C teriitory respectively Explain the factors that determine the size of A an animal s home range and B an animal s territory In your answer elaborate how the determinants of home range vs territory size differ The primary difference between a home range and a territory lies in the cost of defending a territory A List and provide a brief explanation of 5 costs of territorial defense B List and provide a brief explanation of 5 benefits of exclusive use of space Explain how an ecologist can detect teriitoriality in real animals out in nature Provide two different types of pattems andor observations that would tell this ecologist that individuals in that population are defending teriitories Dispersion patterns of animals can indicate whether the animals are territorial or not A List and describe the three types or categories of dispersion B Which of the three pattems of dispersion is indicative of teriitoriality Study hint three classes of dispersion pattems along a continuum clumped aggregated random and uniform dispersed C Explain why this pattern of dispersion would result if animals are teriitorial D Give an example from lecture or the textbook of organisms that are dispersed in this way A Identify the tradeoffs that determine optimal territory size B Sketch how these tradeoffs vary across territory size and explain how this dictates the optimum Discuss using a sketch to help explain your answer how A shifts in habitat quality will alter 6 EVE 101W08 49 o v 45 46 47 50 48 Midterm 1 Questions the optimal size of a teriitory and B how the optimal territory size depends on the cost of defending it Answer the following questions about the model of optimal territory size Study hint a real exam might pick one or more of these questions Draw a simple graph depicting the basic optimal territory size model Be complete Be sure to label everything you draw Now give one assumption that the optimal territory size model makes about teriitoriality in animals Give one prediction that this model makes about the optimal size of an animal s teriitory How well do real animals conform to this prediction Describe a test of the model of optimal territory size How well did the real animals fit the predictions Study hint pick a documented example which explicitly tests or re ects the parameters of the model We covered two good examples in lecture A List as completely as you can the 1 benefits and 2 costs of defending a teriitory B Explain two pattems of territories that arise from considering both the costs and benefits of territorial defense Study hint for B This part of the question focuses on either the assumptions or predictions of the optimal territory size model a wide variety of correct answers is possible but make sure that your answer is specifically directed at the optimal territory size model and precisely worded Answer the following questions about the model of optimal territory size Study hint a real exam might pick one or more of these questions a Draw a simple graph depicting the basic optimal territory size model Be complete Be sure to label everything you draw b Now give one assumption that the optimal territory size model makes about teriitoriality in animals c Give one prediction that this model makes about the optimal size of an animal s teriitory How well do real animals conform to this prediction d Describe a test of the model of optimal territory size How well did the real animals fit the predictions Study hint pick a documented example which explicitly tests or re ects the parameters of the model We covered two good examples in lecture A Use the graphical model of optimal territory size to make predictions about how the size of the territory that an animal defends depends on the cost of that defense B How can an anim reduce the cost of defending a territory A List and explain five mating systems found in nature B How do they vary with respect to number of mates sought by each sex and the amount of parental investment made by each sex Consider a species that is facultatively polygynous A What might a simple model predicting 7 EVE 101W08 49 Midterm 1 Questions the degree of polygyny consider Hint you can reproduce the simple model we covered in class B Under what conditions would we expect polygyny to be more common than monogamy You may use the polygyny threshold model to guide your answer B What species is an example of facultative polygyny and how does its biology fit the simple model and its predictions Give two examples of mating systems and explain how ecological conditions lead to their evolution Hint a mating system is depends on the ecological setting of that species and not its evolutionary history or phylogenetic relationships Resource abundance and defense or not dIives the evolution of different mating systems You can contrast the resource defense polygyny example with the lek polygyny example EVE 101 W 08 Lecture 1 Page 1 Lecture 1 outline Introduction to ecology and Review of evolution I Introduction to the science of ecology A Importance of ecology B What is ecology C Scientific questions in ecology II A quick review of evolutionary principles A Introductory remarks B Selection C Ecotypes Lecture 1 Introduction to EVE 101 amp Review of evolutionary principles I Introduction to the science of ecology This course will cover the pIinciples of the science of ecology It is not a course on environmental awareness However in this course we will take the viewpoint that humans are a species really no different from any other in that Homo sapiens is subject to the same ecological pIinciples as all other species We depend on the functioning of a biosphere and the ecosystems within it for our very existence Thus we will spend time in EVE 101 applying the pIinciples of ecology to humans In fact that is a good way to begin I will first tell you why the science of ecology is important to you and then discuss what the science of ecology ies to explain about the physical world A Importance of ecology First let s consider the importance of the science of ecology before I tell you what it is These are scary times The world environment may be made uninhabitable for humans in a few more generations as the human population continues to grow at a fasterthanexponential rate Many non human species will have gone extinct if they have not already Never before in the history of life on earth has a Single species dominated the entire biosphere possibly making it uninhabitable for life It is not new that living things affect the entire character of the planet Earth A thin film exists on this planet known as the biosphere that makes Earth fundamentally different from planets that do not have such a wealth of living beings Mars and some of the moons of Jupiter may indeed have life on them too but life has not become as abundant there as on Earth For example when living organisms that are capable of photosynthesis invaded the Earth s terrestn39al environments the entire atmosphere was EVE 101 W 08 Lecture 1 Page 2 transformed to provide better support for all living things As a result many taxa invaded the land surfaces and this period of Earth s history saw a sudden rise in the number of species something that we now refer to as biodiversity Now humans are having affects on the biosphere that cause it to be less capable of supporting life as we know it This has also happened before in Earth s history There have been mass extinctions before when megavolcanic explosions and meteors that have changed the earth s atmosphere for decades But now a single species specifically the human population and its rapidly developing technology in the 21 century are using up the planet s resources at a staggering rate and also causing waste products to build up in the biosphere Unlike meteors humans can think about what they do and contemplate their future and the future of the planet What should we do in the face of our species impact on the biosphere I would urge you not to get so depressed or afraid or paralyzed and say quotThere s no hope so let s eat drink and be merryquot or alternatively go into denial and claim that people concerned about the environmental changes are exaggerating or are leftwinged extremists Instead we should realize the profound importance of ecological principles and environmental ethics and try to change our own lives and lifestyles Saving the biosphere will require that humans make a profound change in their philosophy and world view This change will not be easy and we humans probably won t do it until we re pressed to the edge of extinction As an ecologist I can clearly see that humans are just as subject to the laws of nature or more correctly we should say the principles of ecology as any other species whether they like to think that they are or not A well known environmentalist said quotEnvironmentalism has less to do with solving air pollution global warming and saving endangered species than it has to do with the human race redefining itself so it is able to live in a finite worldquot As late as the 1950 s and 1960 s people really thought there could be a new frontier such as happened in the past with the European expansion and overpopulation of the North and South American continents People said that we can turn to the oceans or space Now I hope we can see how foolish such a view is The oceans are even more fragile than the terrestrial environments and they have been pushed to their limits by the 1990 s by pollution global warming and overexploitation of fisheries We have seen many pictures now of the truly precious quotblue planetquot from space we know that there is not another planet like the Earth out there in the Universe for many thousands of light years The human race has to live within finite resources or go extinct Human economies cannot grow forever quotsustainable growt quot and quotsustainable developmentquot are oxymorons My own view is that the species Homo sapiens is just as quotnaturalquot as anything else that exists in the universe I also respect the multitude of cultures and belief systems that humans have However as an ecologist I can extrapolate from ecological principles and see that the human species is headed toward selfdestruction and toward making profound changes in our biosphere Within that framework I would advocate that we alter our belief systems to allow humans to exist in a stable and nondestructive relationship with the rest of the biological world on this planet This course will emphasize ecological principles as based on latest scientific findings and present for you the rules by which plants and animals persist on the planet living within the limits of their environment or not as the case may be As we go I will let you know how these principles affect humans or tell us how humans are affecting the biosphere on our single planet the Earth This is not an environmental awareness course You can best benefit from an environmental studies or conservation biology class after you have learned basic ecological principles Beyond this quarter look out for more advanced courses in EVE 101 W 08 Lecture 1 Page 3 EVE EST and WFCB and especially for small senior seminars such as the EVE 190 that I occasionally offer I would consider this course EVE 101 to be a success if each of you permanently make sound ecological principles a way of life as you leave UCD and go out into the world Each of you will make a significant impact on the planet for better or for worse I hope that as many of you as possible will lessen your ecological impact on the biosphere as you lead your lives and even improve this planet for future generations of humans and the many other species with share the biosphere with B What is ecology Readings Molles Chap 1 pp 210 Ecology is a relatively new science it was established at the turn of century and not surprisingly the science of ecology is changing its own definition its own view of itself as time passes In this course I will interpret quotecologyquot as the science that seeks to understand the distribution and abundance of organisms A WORKING DEFINITION An ecologist asks quotWhat determines the distribution and abundance of organisms quot Various other definitions of ecology fit into this working definition for example Ecology can be considered the study of the relationships between organisms and their environment This definition itself can be ambiguous because it leaves vague what kinds of relationships are involved The important thing to keep in mind is that ecology is the study of how organisms interact with their physical environment how the physical environment affects them and how organisms interact with each other that is their biotic environment It might be better to say quotinteraction between physical and biotic environmentsquot In any case this definition has a major strength because it acknowledges that living systems interact with physical systems in ways that have profound effects on those physical systems A major question in the field of physics is why some planets develop a biosphere and what the physical consequences of having a biosphere are Ecology has many different conceptual sublevels each of which requires a somewhat different scientific approach These conceptual sublevels parallel the course schedule Individuals The ecology of individuals focuses on their physiological behavioral and morphological characteristics and how these characteristics allow them to interact with their environment and each other At this level we focus particularly on 1 how individual organisms interact with their physical environment physiological ecology and functional morphology together known as functional ecology 2 within a species how individuals interact with each other behavioral ecology 3 how and why individual organisms live their lives deciding how much to grow when and how much to reproduce how long to live life history EVE 101 W 08 Lecture 1 Page 4 Populations To me this sublevel is the heart of ecology I am a population biologist Populations are groups of individuals of the same species These individuals do things eat mate escape predators etc that ultimately lead them to produce offspring Collectively then individuals survive and reproduce This process results in population growth which is the change in numbers of individuals with time A large part of the science of ecology concerns itself with how numbers of individuals in the population changes with time We call this for shorthand population behavior We can apply ecological principles to manage populations If we study the factors that affect population behavior we can understand what determines which organisms will be found where For example a population might go extinct in one place but thrive in another One place might support a larger population of a given species more individuals than another place and so on An important area at this level is human demography Communities A community is a group of populations of different species that occur in one place Communities might be made up of species that occur in one place independently of all the other species there But more often populations of different species interact such as through predation parasitism competition and mutualism in a complex quotfood webquot Population interactions have great potential for affecting the distribution and abundance of organisms Ecosystems An ecosystem is generally considered to be one level of organization higher than a community in that an ecosystem is made up of 1 every species that occurs in a place ie 1 or more communities AND 2 the entire physical environment Is this an arbitrary distinction between community and ecosystem Yes it is but it is still useful Community ecologists focus more narrowly on population interactions Ecosystem ecologists step way back and ignore many biological details For example they might emphasize how energy and inorganic nutrients flow through all the species that occur in one spot and so ignore populations altogether They might also emphasize enormously long time scales in which population behavior is averaged out over many thousands or millions of years This is in contrast to community ecologists who emphasize shorter time scales under 100 years You need both approaches No one approach or scientist has the ability to focus on all levels and time scales simultaneously Landscapes A landscape might be composed of several ecosystems that are often linked For example a watershed could include upland forest ecosystems riparian forests and oodplain ecosystems and a riverine ecosystem Landscape ecology is a rapidly developing field recognizing the broad geographic linkages between ecological units Again the boundary between levels is not strictly defined but landscapes are more inclusive and can contain distinctly different ecosystems Biomes EVE 101 W 08 Lecture 1 Page 5 A biome is a region containing many separate landscapes which is dominated by a common climate This overriding physical environment in uences the evolution and function of organisms so that a biome is characterized by a certain vegetation typethe plants in that region must adapt to a particular regimen of moisture and temperature In turn the food webs dependent on those plants are characteristic of that biome Biosphere The planet Earth contains a thin living envelope known as a biosphere A planet like Earth with life on it develops completely different surface characteristics than one withoutfor example terrestrial plants are responsible for the current composition of gases in the atmosphere and in particular the high concentration of oxygen 02 Although we currently know of no other planet with life certainly there are many such planets in our universealthough as planets go planets with biospheres must still be very rare From a scientific point of view it will be fascinating to learn how different planets with life have developed different biospheres depending on their exact characteristics just as different biomes develop under different climates From an ethical and aesthetic point of view because our biosphere is so rare we humans should have a responsibility to protect it and allow it to continue to function to support life on Earth We are not the only species to have the ability to affect the characteristics of the entire biosphere but our species has a particularly powerful and potentially destructive in uence on the biosphere This course will emphasize mainly individuals and populations including community Your text quotEcology Concepts and Applicationsquot contains sections on ecosystem ecology which you can review on your own However we have only 10 weeks and we can get through the community level but not more in that short period of time in the formal course work C Scientific questions in Ecology Here is a list of the still answered questions in ecology so that you get a more practical feel for what this course will be about 1 Why are there so many kinds of organisms Or why aren t there more kinds or fewer kinds This is one of the major unanswered questions in ecology Darwin who thought of almost everything we still study today wrestled with this question For some reason there are around 107species of organisms not all are described yet It s not at all obvious why there shouldn t be 102 103 104 or 1010 1015 We now refer specifically to quotbiodiversityquot when we consider the numbers of species in any one place or the total on the planet The new ecological field of conservation biology focuses on understanding the origin and maintenance of biodiversity By the way we may never know exactly how many species of animals there really are were Most species are arthropods and many thousands of them are going extinct right now because of the destruction of the tropical forests There may be over a million species of nematodes and of soil mites and they are also going extinct with the rainforests As you can see answers to this question are vital for facing the crisis of loss of biodiversity on the planet at this moment 2 What is the balance of Nature Is there one Or more technically are there ecological and evolutionary equilibria EVE 101 W 08 Lecture 1 Page 6 3 What causes populations to behave as they do What causes cycles or outbreaks or other variation in population sizes What causes extinctions 4A What determines the length of food chains or the complexity of food webs 4B Are there upper andor lower limits to the number of species that can occur at one place What determines the pattems worldwide in species diversity biodiversity 5 Why do some organisms reproduce once in their lifetimes salmon barnboo agave and others many times Why do some organisms have many offspring and give them little care and other organisms have few offspring and invest greatly in their care 6 Why do some organisms defend territories What determines how many mates an organism has some have many others only 1 in a lifetime 7 Why do some organisms escape predation in one way while other organisms use other methods Conversely why do some predators eat many prey species and others only 1 or 2 prey species In other words why do some organisms specialize and others not And so on This lists goes from the big picture into increasingly more detailed questions In the course we ll do the opposite and build from principles of quotindividual ecologyquot to wider perspectives At the end of the course we hope to have some understanding of what causes the global pattems in the distribution and abundance of species II A quick review of evolutionary principles Readings Molles Ch 8 pp 185192 195202 A Introduction Evolution is fundamental to understanding life on Earth as we know it Therefore all fields of biology have evolution as an underlying paradigm A paradigm is a fundamental assumption in a particular field that govems how every scientist in the field views the world or at least the part of the world under scientific study in that field For example in physics before Copernicus the paradigm was that the earth was the center of the universe Other paradigms include more recently the Bohr model of the atom Big Bang theory of the universe and other such grand assurnptions Evolution may be more or less important to a particular biological field depending on what the focus of the field is Most cell and molecular biologists need never think about evolution although it is clearly important in how cells and biological molecules are structured However these scientists focus specifically on mechanisms HOW cells work and not WHY they might have evolved to work that way Ecologists think about evolution much more often than cell biologists In fact an understanding of an organism s ecology typically requires a strong foundation in the principles of evolution And conversely the study of evolution is very dependent on understanding ecological principles A famous ecologist GE Hutchinson wrote a book entitled quotThe Ecological Theatre and the Evolutionary Playquot which summarizes the intimate relationship between ecological and evolutionary processes Finally Charles Darwin was the EVE 101 W 08 Lecture 1 Page 7 first real ecologist in the science as we have come to know it and in his book On the Origin of Species he poses many ecological questions that are still not answered today Your textbook by Molles states that much of what ecologists study is meaningful only in the context of evolution So in this course we will pay attention to evolution particularly at the start Because evolution is so important we will spend some time reviewing it now Evolution can be defined as follows 1 Evolution is the change in the quotgenetic structurequot of the population More specifically this means that 2 Evolution is the change in the frequency of alleles genes in a population WHY this genetic change occurs very often has to do with ECOLOGICAL conditionsDarwin was one of world s greatest naturalists He thought of evolution because of the ecological pattems that he saw This is why we want in an ecology course to remain founded in the fundamental principles of evolution The mechanisms for evolutionary change are 1 mutation 2 genetic drift 3 gene ow and 4 and most importantly of all selection We shall spend all of our time here considering the process of evolution by natural selection because we are most interested in how evolution occurs as a result of the ecological environment in which an organism occurs B Selection The mechanism behind evolution is the process of selection Darwin concentrated most on quotnatural selectionquot which is also known as quotindividual selectionquot Natural individual selection is he process by which frequencies of alleles enhancing reproduction and survival increase in a population through time It is also viewed as the differential reproduction and survival of 39 quot 39 within a l l 39 some 39 quot 39 reproduce more and survive better than others Thus some individuals contribute relatively more genes to future generations than others Thus we define working definition of fitness the number of offspring that it leaves relative to the average number of offspring in that population RELATIVE FITNESS And we can develop a working definition of adaptation in the evolutionary sense Adaptation is a process by which the average fitness of individuals in a population increases with time That is through the process of natural selection individuals in each generation survive better and leave more offspring compared to the previous generation EVE 101 W 08 Lecture 1 Page 8 Now let s see how natural selection works through the concept of ecotype An ecotype is a population that is LOCALLY ADAPTED to ecological conditions at one location Keep this definition in mind as we go through some more concepts needed to understand the process of natural selection The local population is formally a deme which is in turn the setting for natural selection Evolution and Ecology have this major feature in common the population is an central entity to both fields Earlier I mentioned quotpopulation quot as a level of organization Most basically it is a collection of individuals But we need to know a little bit more about it to understand how the population functions as a biological unit The strictest definition of population is to define it as a single deme A deme or population in the strict sense is a group of individuals among which mating occurs randomly This does not mean that individuals are promiscuous or totally indiscriminate or that they don t stay with their mates etc It only means there is no genetic bias in how mates are chosen The requirement of random mating has an important implication The result of random mating is that genes are mixed among individuals in the population in each generation We might also refer to a deme imprecisely as a gene pool We define population or deme this way to understand gene ow and changes in gene frequencies whichis the basis for evolution So a demebased definition of quotpopulationquot is an evolutionary definition To understand the ecological functions of populations without genetic change we will use a very similar definition of quotpopulationquot so this definition is a useful one This definition has important implications for how natural selection works The deme can determine the ideal conditions for natural selection to occur depending on how the scale of the deme matches the scale of the environment in which it is found 1 That the population is essentially closed That is immigration and emigration is negligible Of course in nearly all populations some immigration and emigration occurs as individuals move between populations carrying their genes with them Depending on how mobile the organism is immigration amp emigration might occur frequently or rarely 2 There is no genetic or geograhic bias in how mates are chosen This feature means that allele frequencies are quotfreequot to change with each generation as a result of selection 3 A deme will therefore be restricted geographically depending again on the mobility of the organism But very few species have one population that is worldwide Very rare species might be just one population however such as the whooping crane about 150 individuals that all live and migrate together Most species are collections of populations In other words most species are not perfect demes but are groups of demes between which some genes may quot owquot with immigration and emigration but not perfectly randomly We might say that there is a quotmetapopulationquot made up of smaller imperfect demes Nothing is Nature matches our ideal of course but the deme is a useful concept to start from Review of the process of natural selection 1 Genetic variation is essential Variation occurs among individuals within a population That is some individuals within a population have different alleles than other individuals 2 Many more offspring are born than can survive to reproduce later in their lives Whether an individual does survive to reproduce depends on its genotypethe alleles that it possesses relative to others in the EVE 101 W 08 Lecture 1 Page 9 population 3 Different phenotypes have different rates of survival and reproduction different quotfitnessquot The genotype determines the phenotype or how those genes are actually expressed and natural selection works on the phenotype Some individuals possess traits that allow them to survive or reproduce better than other individuals In their lifetimes they produce more offspring than other individuals in the population 4 By definition individuals with higher fitness leave more offspring Those offspring possess those alleles that enhance reproduction andor survival In this way genes alleles enhancing survival and reproduction increase in the population with each generation This is basically the process of natural selection In other words individuals possessing genes that enhance their ability to survive andor reproduce will leave relatively more offspring that possess these particular genes and so on through time If the environment does not change we can expect the average fitness over the entire population to increase with each generation In other words organisms become quotadaptedquot to their environment In this context can you see why is the deme the ideal setting for natural selection So ecology is the setting in which evolution takes place With each passing generation organisms in a population become more adapted to their environment This is where ecology comes in C Ecotypes To wrap up this review of evolution we can apply these principles to our first ecological concept that of the ecotype An ecotype is a locally adapted population that is a population adapted to local ecological conditions In section we will be covering some examples of important ecotypic populations in California and focus on how ecotypic differentiation occurs by natural selection Ecotypes develop when most of the conditions of the ideal deme are present We cover them in this course because ecotypes illustrate not only how natural selection works but also how important the ecological setting is in guiding natural selection 3 conditions leading to development of locally adapted populations otherwise known as ecotypes geographic variation in environmental conditions abiotic or biotic natural selection on a character related to local environmental conditions limited gene flow relative to variation in environmental conditions Under these conditions natural selection occurs in each generation to the environmental conditions found in that local geographic area With time the average fitness of the population increases as a result of this natural selection This happens because gene flow is restricted and thus natural selection can respond to EVElOl Lecture 5 Page 1 Lecture 5 outline Home range territoriality and mating systems Readings Parts of Ch 6 7 and 9 Molles doesn39t much cover this topic so we will depend on class notes and handouts I Introductory remarks and overview II Home Range 0 A De nition 0 B Function of a home range 0 C Characteristics of home ranges III Territoriality o A Background 0 B Patterns and characteristics of resource based territories o C Theory of OPTIMAL TERRITORY SIZE explain B o 1 Assumptions 0 2 Predictions o 3 Tests IV Mating Systems includes mate based territories o A Background 0 B Classi cation of mating systems 0 C Ecological aspects of mating systems Section 4 revised January 17 2008 Molles 43911 edition pages 2008 Catherine A Toft EVElOl Lecture 5 Page 2 Lecture 5 Home range territoriality and mating systems How individuals use space I Introductory remarks and overview This set of topics logically follows foraging because foraging is the primary basis for most home ranges and many territories in animals A more general View of this lecture 393 topic is that it is about an individual 393 use of space We will focus on the ecology of mobile animals Because they are mobile they use home range and defend territory space in ways not truly comparable to plants and sessile animals However plants and sessile animals use space in very explicit ways indeed exactly because they are sessile their use of space is critical from both ecological and evolutionary points of View For example plants can forage underground using their roots the volume of their roots can vary in size depending on resource availability text pp 1523 exactly as an animal can increase or decrease the size of its home range or territory depending on food abundance Plant and sessile animals can be aggressive about space they can respond physiologically by growth pushing out other individuals or by chemical warfare allelopathy However in EVE 101 we will stay with the traditional topics of behavioral ecology applying mainly to mobile animals simply because of time limitations How animals use space in turn leads to the topic of mating systems because mates are an important resource distributed in space and many mating systems are based on the defense of space and resources such as food that are important to attracting mates and raising young quotMating systemquot refers to the way in which individuals of a given species accomplish sexual reproduction both ecological and evolutionary points of View including how mates are chosen how many mates are chosen and in particular what factors are in the best interest of males and females This topic encompasses all types of organisms most have some type of anisogamy which means separate different sexes or mating types bacteria fungi plants and animals Most scientific work in this area began with animals hence the concept that plants quotmatequot The principles of how mates are chosen by individuals are the same regardless of the type of organism In EVE 101 we will only brush on this topic the study of mating systems occupies a large part of courses on behavior and behavioral ecology In this course we will limit our discussion of mating systems to explore brie y how ecological conditions affect how an organism finds and chooses mates We will cover this material primarily in the Section on mating systems 2008 Catherine A Toft EVElOl Lecture 5 Page 3 II Home range A De nition A home range is simply where an animal goes during its activities A formal definition could be quotthat area traversed by the individual in its normal activities of food gathering mating and caring for youngquot The important feature of a quothome rangequot is that it contains everything the individual needs food and other lifesustaining substances such as water mates nests dens or other requirements for caring for oiTspring protection from predators or physical environment The quothome rangequot of an animal can be complex it depends on the time scale that you consider along with the age sex and other characteristics of the individual For example an animal may shift its home range during different parts of the year and of the life cycle An animal could have one home range during the breeding season and another during the rest of the year as for example a migratory animal would have Thus when you start to generalize about the home range of species of animals you should specify the period of time and the parts of the animal39s life history that you wish to understand In general the concept of home range is used for mobile animals that are relatively sedentary during at least some part of its life cycle Some animals are truly nomadic never visiting the same location again except possibly during breeding season The most extreme example might be pelagic invertebrates in the ocean these animals simply oat at the whim of the ocean currents For such species the concept of home range would be unde ned and not biologically very relevant Rather we want to consider in the next section the functions of a home range and why a mobile animal might want to revisit the same areas during parts of its life cycle B Function ofa home range We should take some time here to consider what might be important about the space that an individual uses and therefore why an individual might want to use the same space repeatedly We have been discussing food and foraging and primary among the functions of a home range is a place to nd this food We can be more general and include all resources that an organism uses The following are the major functions of a home range 1 A place to acquire important resources including food energy or nutrient sources water mates shelter thermal microsites and so on whatever the individual requires to promote its survival growth and reproduction 2 Familiarity Even a nomadic organism could find the above resources somewhere but a critical advantage of having a home range is that an individual can have knowledge of the location of these key resources Examples of how this familiarity can affect an organisms tness include A A refuge from the environment or predators If an individual can nd shelter quickly because it knows the locations of hiding places this knowledge could be a great 2008 Catherine A Toft EVElOl Lecture 5 Page 4 advantage for promoting survival B Knowledge of the location of food or other resources are seasonally available resources An example of this advantage would be howling monkey troups which are led by the troup matriarch She knows when and where rare fruits will be ripening or seasonal trees will be ushing out new leaves In this way a troups foraging ef ciency can be increased C Characteristics of the home range Ecologists might want to measure characteristics of a home range the most revealing of which is its size The size of a home range is related to fundamental properties of the animal in particular its ecophysiology and its foraging mode This relationship is part of the study of quotscalingquot in the eld of quotfunctional ecologyquot As the terms suggest ecologists study the physiology and morphology of different types of organisms and they attempt to understand how organisms function at different scales One critical scale in the eld of ecophysiology and functional ecology is the size of the organism Different sizes of animals for example have different pergram metabolic rates different absolute total metabolic demand different ef ciencies of locomotion thermoregulation and in other ways that affect its energetic need These relationships affect population patterns such as density and are affected by other ecological factors such as position in food webs Given the size of an organism what kind of space and resources does it need or can it use Why We can study this under the topic of home range or we can take this question to the next level Unit 11 to see how abundance and distribution of organisms of different size scale to the population level Molles Ch 942446 Here we can relate the size of the animal to the size of its home range Not surprisingly the larger the animal the larger the size of its home range Notice that the relationship of body size and homerange size is plotted on a loglog plot Advanced question Why How does body size scale with metabolic rate hrsizehtm Home range size versus body size quotHumers39 IV I Croppers Home range size log hectares Body Weight Mg kg 2008 Catherine A Toft EVElOl Lecture 5 Page 5 biomhomehtm Biomasshectare by trophic level U weasel lynx meateaters gt i cou ar g g 0 omnivores skunk fox black bear mouse seedeaters chipmunk 2 squlrre vole 399 5 follage eaters woodchuck m deer Biomass kghectare We can summarize the factors determining home range size as follows 1 Energy needs a For bodies ofa given size The larger the body size the more tissue needs to be supported therefore the greater resource energy needs Thus the larger the body size the larger the home range For a given basal metabolic rate The smaller the animal the greater the basal per gram metabolic rate which to some extent reverses the trend in a endotherms have a higher metabolic rate than ectotherms Thus for any given body size animals with a greater metabolic rate will have greater total energy demands and require a larger home range For a given type of locomotion Some types of locomotion are more energetically costly to perform others are more efficient for a body of any given size some environments require more effort for a range of locomotion types For example ight is very energetically costly so for any given body size animals that y have a greater home range size than animals that swim similar mechanics of locomotion 2 Position in a food chain Herbivores which eat plants have smaller home ranges for any 2008 Catherine A Toft EVElOl Lecture 5 Page 6 given body size than animals that are omnivorous or carnivorous This pattern presumably is because population density varies with position on a food chain perhaps because of the ef ciency of energy transfer between trophic levels So plants are more dense than herbivores which are more dense than omnivores which are more dense than carnivores In general population density varies with home range size such that animals with smaller home ranges occur at higher densities Thus herbivores have smaller home ranges than do carnivores III Territoriality A Background A territory differs from a home range in one important feature DEFENSE Defense is like it sounds an individual actively chases or attacks other individuals that come into its quotspacequot Importantly the individual invests some kind of cost into defending a territory against intruders and it gains some kind of bene t from doing it 1 BENEFITS Exclusive access 0 a The major bene t is exclusive access to resources food nest sites whatever This area contains enough food for the territory defender mate and offspring or group herd troops ock etc members covering present and future needs 0 b Along with this the territory defender has exclusive access to MATES This bene t applies primarily to males as we ll see when we get to mating systems When would exclusive access be bene cial to an individual and when would exclusive access not matter This question is important in determining whether the cost of defending a resource is worth it 2 COSTS o a Energy Territory defenders engage in heightened activity such as running charging aerial hovering etc all of which have higher metabolic costs than just walking or normal ying Individuals may make metabolic investments in chemicals to mark their territory and so on b Time An animal just like us has only so much time in a day Time spent chasing intruders may be at the expense of time spent in other important activities such as feeding or mating This is an application of the Principle of Allocation c Risk of damage during territorial defense The story you see on TV nature shows that animals fall always short of hurting each other is a myth Individuals often have no 2008 Catherine A Toft EVElOl Lecture 5 Page 7 qualms at all about hurting another individual especially if they can do it without much damage to themselvesthe result may often be death either directly or indirectly to the intruder Territory defenders therefore often in ict damage to intruders on purpose but they therefore risk damage because the other individual is trying to do the same d Increased exposure to predation or elements while the individual is concentrating on other activities The territorial individual might spend more time out in the quotopenquot where predators can see it or spend more time moving again allowing predators greater opportunity to find it Territorial individuals often defend their space at the expense of not eating or not paying attention to their other needs Thus territory defenders are more vulnerable to marginal environmental conditions and may for example starve during storms or other inclement weather B Patterns and characteristics of resource based territories 1 How to detect territories o a Boundaries One easiest way to detect territoriality is to look for an animal defending its boundaries This information can tell you many things how costly the defense of the territory is what bene ts are inside these boundaries and what the overall size of the territory is b Distance between nearest neighbors You may not always see territorial defense in action in fact chances are you will rarely see it more on why later Nonetheless the territory exists and the animal is defending it when you are not looking or has defended it already before you found it Molles Fig 910 914 pp 21720 To detect territoriality you can measure the distance between nearest neighbors ie the potential territory holders and their rivals The null hypothesis is that individuals are distributed at random under the assumption that conspecific individuals do not in uence each other s positions Why is this the null hypothesis If individuals defend territories against conspecifics then individuals do in uence each other s positions in the direction of driving individuals away from the territory holder The alternative hypothesis is that individuals will be farther apart than expected by chance random If you measure the distance between two nearest neighbors and do that many times you can test whether the distance to the nearest neighbor is greater than you expect Under these conditions we might expect a uniform distribution of individuals in habitat ie all individuals are about the same distance apart Why What is the expectation of distance to nearest neighbor if individuals are distributed randomly Dispersion of individuals can reveal many interesting ecological processes not only whether they are territorial More generally uniform dispersions are indicative of some kind of competition or interference between individuals typically those of the same species Uniform dispersions are typical of plants that compete for resources too text page 1712 even though they are not quotterritorialquot 2008 Catherine A Toft EVElOl Lecture 5 Page 8 2 Characteristics of territories that we want to explain To explain why animals defend territories a scientist can first turn to explaining important characteristics of territories o 1 Resource density When are territories defended If resources are too abundant or too scarce many animals are observed to stop territorial defense Why 0 2 Size area defended There might be a number of characteristics of territories we could try to understand but the single most important one is territory size That tells us a lot about why animals are territorial and about the factors affecting territory holders Because size is the most informative characteristic about territories it is also easiest to measure from now on just concentrate on ONE feature size C Theory Of OPTIMAL TERRITORY SIZE not covered in Molles 1 Background Like optimal diet a powerful way to proceed is to make some simple models to predict what an animal SHOULD do and then see what it DOES do If our predictions match the observations then we can be satisfied that we have a good understanding of the causes of territoriality Trade offs in territory characteristics Territory size The larger the territory 0 Benefits the more food availablemates available 0 Costs more intrudersunit timethe more costly the act of expulsion have to chase them farther Define OPTIMAL as the size area that maximizes the difference between the bene ts and the costs and thus allows the largest possible net bene t In what follows we will think of FOOD as the primary quotbenefitquot in defending a territory although a number of other currencies could be importance in territorial defense 2 A MODEL of optimal territory size assumptions and form of the model This model is designed specifically for an energy maximizer with a processing constraint you ll see why in a minute Thus it is an economic model the benefits from the territory are in units of energy gained per unit time the costs are in units of energy invested or risk per intruder LECTURE HANDOUT You see in this simple model the optimal size of a territory which maximizes the difference between benefits accrued and costs of defense 2008 Catherine A Toft EVElOl Lecture 5 Page 9 Key features AS SUMPTIONSof the model 0 1 Upper limit to bene ts Usually bene ts asymptote for a given territory size An energy maximizer might want all the energy potentially available to it linear increase in bene ts but more realistically it might have an upper limit on the time it can spend foraging so after a point it can39t get any more bene ts from a territory even if there are more resources present This is inherently true of energy maximizers with a processing constraint 0 2 Costs The costs of defending most territories will be non linear because territory size increases with area ie the quotsquarequot and you might expect the larger the area the proportionately harder to defend it and be everywhere at once Whatever shape of the two curves there has to be some NET gain somewhere which could not be available without some investment or a territory is not worth defending above the point where lines cross Under any other conditions then we would expect animals to stop defending the territoriality because doing so is not pro table ie there is no net gain The optimum size of territory to defend will be widest separation of the cost and bene t curves Now let s vary parameters of this model and see what happens Another way to view this process of analyzing the model is to think of it as comparing two territories which differ in only one respectall else is held equal 3 Predictions and tests of the model 1 Allow bene ts to vary First and most obvious thing to do is see what happens when one territory is higher in quality than another That is there is more foodunit area higher density resources This change causes benefit curve to go upward to asymptote sooner and at a higher value on the quotbene tsquot axis for any given territory size All else equal cost function does not change the optimum territory size goes down Why You get same bene ts in a smaller area which is less costly to defend The speci c size of territory will depend on exact form of these functions but you can certainly as we do here make a relative comparison and therefore relative prediction about two different territories PREDICTION 1 The richer the territory ie the more food it has per unit area the smaller it will be for a given cost of defense In other words a higher cost of defense is not necessary if the territory holder can get enough resources in a smaller area Test of Prediction 1 examples lizards and harriers Lizards In many species of lizards males are typically larger than females and they need more food Larger males can also defend larger area with the same cost compared to smaller males because they are simply largerthey can run faster and scan a wider area for intruders So a large male39s territory size is typically larger than that of a smaller male In an experiment on spiny lizards the scientist supplemented food and found territory size to 2008 Catherine A Toft EVElOl Lecture 5 Page 10 DECREASE relative to a control Then she removed the food supplement and the average territory size went back upsee transparencies in class Her results suggest that food is primary motivation for territory in both sexes Harriers old name marsh hawk Both sexes defend a territory based on mouse availability even though harriers prefer birds to eat But birds are much harder to catch and unpredictable in abundance Harriers therefore use mice for a quotstaplequot and the size of their territories is based on mouse abundance 2 Allow costs to va The more costly territory to defend will have the cost curve rising faster relative to the size of the territory see your handout PREDICTION 2 The more costly a territory is to defend the smaller the optimum size for a given benefit function Of course net bene ts will be less at quotoptimal sizequot in costly territories compared to territories that cost less to defend Again we can separate the speci c prediction of actual territory size in a given situation versus the relative prediction of 1M the territory size will change increase or decrease when a given condition varies Tests of prediction 2 are more complicated than the study we considered for prediction 1 One hypothesis is known as the Dear Enemy hypothesis the idea is that territory holders lower their costs of defense making a territory more profitable by getting to know their neighbors that is individuals that hold adjacent territories However Ethan Temeles studies harriers a raptorial bird common around Davis and refuted the Dear Enemy hypothesis In contrast to the prediction of this hypothesis female harriers were more likely to escalate fights with neighboring territory holders than against oaters which are females with no territories and males which do not hold territories He reasoned that the adjacent territory holders presented the greatest risk of losing territory or the resources therein hence cost of defense should be invested in the neighbors and not the oaters Nonetheless his study does confirm a general pattern that territory holders try to reduce cost of defense somehow in order to gain more profit from territories 2008 Catherine A Toft EVElOl Lecture 5 Page 11 III Mating systems including matebased territories A Background De nition mating system is de ned as quotensemble of behaviors and physical adaptations speci c to mating and the social consequences of these behaviorsquot While the topic of mating systems would be covered more extensively in courses in behavior or evolution in EVE 101 we will go over mating systems brie y for three reasons 0 1 Mating systems are far more A J J on 39 39 Jquot eg ecology than phylogenetic heritage So is an obvious subject for this course on ecology We concentrate on this principle in section 5 2 This topic is a prelude to the next unit on population growth obviously mating is involved 3 Mating systems are intimately involved with what we just studied foraging ecology energy for reproduction and territoriality defense of space for access to food or mates Mating systems often involved foodbased territories at least in animals B Types Of mating systems The evolution of mating systems and therefore types that we see now revolves fundamentally around the asymmetry of the two sexes in investment in the gametes and offspring same as energy maximizertime minimizer o FEMALE large expensive gametes Large stake in EACH mating 0 MALE small inexpensive gametes Small stake in EACH mating A female39s main concern is to maximize investment of energy and time directly into gametes Because of limited time and energy this means investing in FEW gametes with large investment in each relative to male A male39s main concern is to maximize number of gametes that result in successful fertilizations which often means to maximize the number of mates Why He makes a small investment in each maximizes his fitness with MANY offspring relative to a female Therefore he will mate with more than 1 female This basic dichotomy explains many mating systems but not all as follows The actual care of gametes can 0 1 accentuate this difference if female cares for gametes and young which is very often the caseshe already has made a larger investment in gametes than did the male and so she continues to support this investment with more time and energy or 2008 Catherine A Toft EVElOl Lecture 5 Page 12 o 2 decrease this difference if the male invests in young beyond the gamete stage which happens reasonably often too Such investment of males in care of the offspring results in interesting quotrole reversalsquot Why quotreversalquot We expect females to perform certain roles involving care of offspring by definition When the male in a given species takes over those roles females are free to engage in other activities Thus in some species males perform activities more often associated with females and vice versa So the form of a particular mating system will depend on 1 care of offspring beyond the gamete stage when why also topic of later lecture 2 which sex or sexes contribute to care beyond the gamete stage and why EG Types of mating systems Monogamy one individual of each sex stays together during breeding event or lifetime 0 Polygamy more than one matebreeding system or lifetime 0 Polygyny male has many mates females one mate 0 Polyandry female has many mates male one mate 0 Polygynandry both sexes have many mates 0 Promiscuity both sexes mate indiscriminately Really NO mating system What determines the mating system of a given species Answer to this question can be approached as follows 0 1 What will maximize the tness of a female and a male under given ecological conditions 0 2 Which sex invests in offspring beyond the gamete stage and why We can t go into that much detail about how mating systems evolve but here is a general summary based on investment of each sex in offspring Lecture handout p 15 o MONOGAMY quotParental carequot Offspring are invested in extensively for some significant portion of the period when the offspring is still sexually immature Both sexes are required for care ofthe young because it is such a quotbigquot job 0 POLYGYNY Male invests nothing but sperm in care of the offspring he may invest in defense of a territory that attracts females While this may constitute a form of quotparental carequot his main interest in maximizing the number of his mates Females in contrast 2008 Catherine A Toft EVElOl Lecture 5 Page 13 invest heavily in offspring and often there is extensive maternal care POLYANDRY Simply the opposite of polygyny Males invest in care of the offspring beyond fertilization females maximize their reproductive success by mating with as many males as possible This condition is rare probably because of how we de ne quotmalequot and quotfemalequot in the rst place Usually production of eggs is a considerable investment to begin with so females are already inclined to extend care to offspring as well However in some species there is extensive care of offspring which can be and is done by males in these systems POLYGYNANDRY Both sexes have multiple mates and either sex can invest in offspring Some systems thought to be polyandrous may be polygynandrous for the reason mentioned above Females should be reluctant to stop investing in already expensive gametes o PROMISCUOUS Both sexes have multiple mates and neither sex invests in offspring beyond the production of gametes Most common in marine invertebrates which shed gametes into the open ocean Otherwise promiscuity is rare as there is usually an advantage to some degree of parental care and in any species that invests in offspring individuals bene t from being selective about who they mate with While these mating systems were de ned with animals in mind they also apply to plants and animals The patterns in plants and animals should be very similar with male individuals investing more in numbers of gametes and the ability of those gametes to disperse and with female individuals being selective about which male gametes fertilize her eggs How can a plant be selective Once a pollen quotgrainquot arrives at a ower the process of fertilization of the female plant s ova has only just begun A pollen tube must grow and reach a receptive ovum egg cell There are many sophisticated mechanisms for the reception or not of pollen tubes by the female plants owers have a limited period of receptivity and so on Even in plants with owers of both sexes producing pollen vs seed the same strategies can be used as most plant species are quotoutcrossingquot and receive pollen from another individual In such cases a plant will have typical female quotstrategiesquot for the females owers and male strategies for the male owers Here and with other topics a plant s physiology is a form of quotbehaviorquot Choices are expressed as physiological responses In the evolutionary sense a plant s choice by physiological mechanisms is exactly the same as an animal39s choice by behavior and cognitive mechanisms 2008 Catherine A Toft EVEl 01 Lecture 4 Page 1 Lecture 4 outline Foraging ecology I Introduction Overview of a forager searching heterotroph 39 A Needs and constraints 39 B Premises assumptions 39 C Types of choices that foragers make 11 Optimal Foraging Theory Optimal Diet 39 A Background 39 B Rationale to model 39 C Model 39 D Tests of model 111 Types of foragers 39 A Background role of evolution 39 B Interspecific comparisons 39 C Intraspecific comparisons revised January 11 2008 Molles 4 h edition pages Lecture 4 Foraging Ecology Molles Ch 6 especially 63 his lecture begins to look formally at how an ecologist does science Look for boxes that amplify how the scientific method is applied in ecology I Introduction Overview of a forager This subject foraging ecology is at the interface between physiological and behavioral ecology even more than the thermoregulatory behavior of desert lizards Because plants are autotrophs their acquisition of energy falls entirely in the field of physiological ecology However because quotanimalsquot are heterotrophs and must find their food in the environment acquisition of energy in animals and other searching heterotrophs is partly physiological and partly behavioral The field of foraging ecology tries to predict the decisions that any organism would make in the act 2002 Catherine A Toft EVEI 01 Lecture 4 Page 2 of foraging for food prey This goal leads us to make the following distinction Feeding is a physiological and morphological process it includes consuming and digesting food items often other organisms Foraging is a behavioral process it includes searching and capturing prey and the decision making involved in how when and where to search and when and what prey to capture A The Organism s needs amp constraints in food nding Organisms mostly animals get bene ts from food 39 1 energy measured in calories for metabolism to store for growth migration reproduction producing eggs offspring finding and defending mates competitive ability escaping predators 39 2 water 39 3 nutrients protein nitrogen for enzymes tissue etc carbohydrates and lipids for energy and various functions micronutrients vitamins minerals trace elements However animals also have costs in getting and processing food 39 1 time to forage when time is limited and could be spent on other things 39 2 chemicals and toxins other living beings don39t want to be eaten 39 3 danger and damage again things don39t want to be eaten foragers are exposed to predation while foraging In this course we will learn to think in terms of costs and benefits from both ecological and evolutionary standpoints While it s easy to think of benefits to organisms it39s equally easy to forget that there are always costs Organisms weigh the benefits against the costs and are often faced with something ecologists refer to as quottradeoffsquot We assume that organisms quottryquot to maximize the net benefits total benefits minus the costs We also assume that the net benefits to an organism are directly related to its fitness In the last lecture we saw how plants maximize net photosynthesis which leads to left over energy that a plant invests in growth survival and J quot fitness In this lecture we will apply this concept further Barry Commoner an ecologist famous back in the 1970 s for his environmentalism summarized this principle as one of the three Laws of Ecology quotThere is no free lunchquot A tradeoff is defined by Webster s dictionary as an exchange especially giving up of one benefit advantage etc in order to gain another regarded as more desirable In an ecological context we view trade offs as arising from conflicting demands An organism has the choice of exchanging one benefit for another given changing conditions that make one choice more beneficial than another under those conditions Trade offs are necessary because of the principle of allocation which states that all life functions cannot be simultaneously maximized ie all of life s needs maximally satisfied EVEI 01 Lecture 4 Page 3 B Premises in the study of foraging ecology When a scientist begins to propose hypotheses to explain some pattern she or he begins by making a series of assumptions or premises about the processes leading to that pattern Typically these are either fundamental properties that define the question to begin with or they are simplifying assumptions that allow a scientist to start with the simplest possible case from which to build complexity if that is necessary we will talk about the role of quotparsimonyquot in scientific explanations many textbooks discuss aspects of the scientific method in ecology In general scientists start out with the simplest possible model or hypotheses At first students tend to reject this simplifying approach based on the understandable common sense observation that overly simple models are not quotrealisticquot Yet the scientist39s job is not necessarily to describe Nature with total realism in fact that is a minor part of what a scientist does Rather a scientist39s task is to understand the reasons for the existence of patterns in Nature To do this a scientist seeks the simplest possible explanation that will account for the observation and most 39 y to allow the scientist to predict something in advance This goal of seeking the simplest possible sufficient explanation is known as the principle of parsimony The following are assumptions we are making about the foraging process as we begin our search for patterns and explanations includes proposed fundamental properties of foraging and simplifying assumptions to reach the goal of parsimony 39 1 Animals feed quotsensiblyquot evolutionarily speaking Individuals try to get the most benefit for the least cost Specifically they maximize difference between benefits and costs for the largest net bene t doing so will allow the greatest fitness why 39 2 Animals therefore evolve morphology physiology behavior that allow them to feed profitably in their environments 3 Animals and all organisms can39t do everything perfectly or equally well and all organisms face important limits There must be tradeoffs involved Animals make evolutionary and ecological quotdecisionsquot on what to concentrate on or what to put effort into In more precise terms we speak of the allocation of energy time or other currency to accomplish different goals or tasks when energy time or other currency is limited This constraint for all living organisms is known as the principle of allocation Molles p 150 You are already familiar with the principle of allocation in your life You have the following limits You have only 24 hours in each day limited time and you have a certain amount of money in your bank account limited energy If you spend more time studying for ecology you have less time to study for organic chemistry You have constraints because you have to sleep sometime eat sometime etc If you spend more money on rent you have less money to spend on food These choices all represent trade offs more time on organic chemistry means less time on ecology 2002 Catherine A Toft EVEl 01 Lecture 4 Page 4 C CHOICES or decisions in the foraging process primarily behavioral These quotchoicesquot or quotdecisionsquot need not be conscious on the part of the organism they make be fixed genetically as a result of past evolution e g quotinstinctquot However many animals in fact are intelligent Animals by nature tend to be mobile heterotrophs that need to detect and act on environmental stimuli In addition they may have to react to multiple possibilities in unpredictable environments Intelligence evolved as a mechanism to allow animals to make good decisions in terms of fitness based on information that they gather from their environment Here we focus on the important process of foraging Important choices include 39 1 How much to eat in units of energytime or effort 39 2 What kinds of food prey to eat Do they need to balance diet or tradeoff costs Factors in uencing these decisions are 39 size and metabolic rate 39 point in the life cycle growth reproductively active adult 39 point in the reproductive cycle amp sex of individual including whether the individual need to produce eggs feed young defend young defend territory or mates 39 3 Where to eat The world is not uniform it is quotpatchyquot or heterogeneous Choices depend on 39 food density and quality in a patch 39 distance of feeding patches to other activities such as dens nests etc 39 risks of predation in a patch or in traveling to a patch 39 presence of competitors in a patch same amp different species In this course we will consider how an ecologist does science You should all be familiar with the scientific method and may already have learned to apply this method in your other science courses In a nutshell the process goes in this order 39 1 A scientist makes an observation about the physical world and measures it somehow this part is the descriptive phase of science In ecology the descriptive phase is often referred to as natural history 2 The observations seem to form a pattern which the scientist seeks to understand In other words the scientist seeks to learn the cause of mechanism for that pattern 39 3 The scientist formulates hypotheses to explain the cause of this pattern or observation 2002 Catherine A Toft EVEl 01 Lecture 4 Page 5 Often the scientists contrasts a quotnullquot hypothesis against an alternative hypothesis quotnullquot then means that the proposed mechanism is not operatng or a scientist can propose several alternative hypotheses the alternatives represent different possible mechanisms 39 4 The scientist finds ways to test herhis hypotheses Tests can take two forms 1 conduct a formal experiments with controls the most familiar way of testing hypotheses to most students or 3 construct a formal theory or model to suggest further data to collect from the physical world Either way prompts the scientist to make further observations that will confirm or refute the hypothesis Chapter 1 gives some examples specific to ecology The following section provides our first example of using a simplifying model principle of parsimony to formulate hypotheses 11 Optimal foraging theory or Theory of the optimal diet 39 A Background 39 B Rationale to model 39 C Model 39 D Tests A Background amp Introduction Molles pp 148 152 The theory of optimal foraging is a simplified theoretical mathematical framework that tries to predict what animals should eat if they foraged quotoptimallyquot In this case optimal is defined as maximizing energy gained per unit time et We assume that maximizing profit during foraging maximizes the individuals fitness We say that the currency to be optimized in these models is energy and that the major constraint is limited time We know that evolution does not necessarily quotoptimizequot anything However we begin our model building process here with a simple ideal prediction How quotreal lifequot deviates from this ideal starting point brings many fascinating ecological details to our attention You could also include other types of currencies such as any of the benefits listed at the beginning of the lecture and you can include any kind of cost or constraint such as we listed 39ust now After we go over this simple et model framework we will quickly review other more realistic considerations However the et approach works surprisingly well to predict the foraging behavior of real animals It is especially effective with predators of other animals seeds and fruits and animals 2002 Catherine A Toft EVEl 01 Lecture 4 Page 6 that eat nectar It is somewhat less effective with herbivores that eat leaves but it still works remarkably well to predict their diets It is as if energy assimilation overrides balancing of nutrients or other trade offs at least in the short run HANDOUT B Rationale Let s go over the situation we are trying to predict amp what we need to consider A Prey types You have a bunch of different food types available in the environment They are not perfectly interchangeable Now we are only considering two variables 39 1 Energy content the energy they contain and 39 2 Handling time the time it takes to pursue capture and eat and digest them Sometimes we lump all the activities after the predator finds a prey as quothandlingquot time Prey can be ranked according to units of et THE QUESTION IS If you rank prey items in order of decreasing et at what point does the predator no longer want to eat a prey type of lower quality In other words what are determines the number of prey types in the diet We can39t compute that unless we know some more about the predator and the environment Assumptions 39 Energy and time are the relevant currencies 39 Forager knows et of all food types upon encounter ie without testing 39 Forager knows all of the i types of food available without exploring B Prey search The predator has to find the prey that it will try to capture There will be some costs of quotoverheadquot of searching for prey There are two types of costs 39 1 Energy The predator uses up energy searching for prey It might be moving around walking swimming flying and this takes energy Or it might be sitting and waiting where there will still be a net energy loss because of resting metabolism This should not depend on the type of prey the predator is looking for but instead it depends on the type of predator and the strategy it uses for finding prey its metabolic rate body size etc We treat it as a xed overhead cost search cost in energytime because we are not comparing types of predators we are only comparing types of prey for one given type of predator 2002 Catherine A Toft EVEI 01 Lecture 4 Page 7 39 2 Search time The predator needs to take time to search Search time does not depend directly on the type of prey either in this model It depends instead on 39 a the type of predator again treated as a fixed cost and 39 b the overall prey density which is especially important in this model because we assume that the predator encounters all the prey types at random SEARCH TIME thus is the average time between going from one prey to the next Assumptions 39 Search energy cost does not depend on the food type but on the type of forager Search time does not depend on the food type but on the type of forager and on the total food density available all types combined Foragers are either searching or handling during the foraging bout they are not engaged in any other activity that takes time such as looking for mates or predators 3 Type of search random We assume that the predator encounters prey in exactly the same proportions as occur in the environment One type of prey is not inherently easier in this model to encounter than another due to any quality that prey might have This assumption allows us to calcuate the number of each food type encountered The probability of encountering any given type of prey is proportional to its relative density So a predator will encounter prey A more than prey B only if prey A is relatively more abundant than prey B not because prey A is easier to see or to detect from longer distances This can easily happen but we are ignoring this complication right now Assumptions 39 Forager searches randomly food types are encountered in proportion to their relative density pi 39 Forager knows the pi of all food types without exploring first C The model That background should make the simple model easy to understand See your lecture handout Note that Molles has this model with different notation on p 149 The two systems of notation are identical which you can show algebraically However I prefer the notation in the lecture handout because it s more intuitive and easier to understand To see what I mean try to explain why the demoninator in the model in your book starts with a quot1 everythingquot That39s not very intuitive to me Can you see how to get from the book s formula to the one below 2002 Catherine A Toft EVEI 01 Lecture 4 Page 8 YT is the ratio of net energy gained over the time it took to gain it Units of kcalsec calmin or whatever the scaling is up to you YT is in units of energytime eg kcal sec Epiei CSTS Y T Etpiti i39Ts x ere YT amount of energy gained per unit time while foraging pi the proportion of food items that are type i e energy gained from one item of type i t time to pursue handle and swallow a single type i item 0 T5 mean search time per item of available food all types average between any two items 39 C5 cost in energy per unit search time 1 In the numerator net energy gained GAIN total The prey types have different energy contents so you need to add up all the prey the predator can take in that time unit Which prey types it encounters will depend on the relative abundance so you weight this summation of energy gained by the proportions of different prey types minus LOSS There will be energy lost to get this prey The predator uses energy per unit time it searched We will clock the time it searched as the average time between two prey items This search rate will depend on the density of prey in the environment 2 In the denominator time is used to eat those prey The predator uses a different handling time with each type of prey item Again to add these up we have to weight the sum according to the different prey types and the proportion of those prey types in the diet And we have to consider the time it searches that is the average time it takes to find a prey item 3 How to figure out the diet First You rank the prey items from best to worst ie highest to lowest et Then You add one at a time to the diet and see how much energytime you get At some point a poor quality prey item will make you lose energytime because it has too little energy or it takes too much time to eat it So the predator eats all the prey types that maximize the et Say the predator ate only the best 2002 Catherine A Toft EVEI 01 Lecture 4 Page 9 prey type and ignored the second best prey type If the second best prey type is pretty good this predator might do better if he ate both the first and second types of prey whenever he encounters either of them And so on However some types of prey might be so poor in quality that the forager actually loses net energyunit time if he bothers to catch and eat it If so it pays the forager to ignore that prey and go on and try to find a better one 4 UNDER SPECIFIC CONDITIONS This above reasoning so far is qualitative What OFT does is try to predict 1 the diet exactly what prey types i are included in versus excluded from the diet and 2 the specific factors that cause the predator to add or to exclude items from the diet and 3 a quantitative estimate of the energy gained by the optimum diet under those conditions of prey density You definitely should go through the handout on your own and that is your homework assignment Let s look at the two problems I already worked out Problem 1 This first exercise works through the process With the particular items we have listed the predator profits from eating types 1 and 2 when it encounters them Item 3 should be ignored because it is very low in energy and even takes more time to eat than the others do at least under the current conditions This brings up the first counter intuitive prediction a food type should be ignored if it is low quality even if it is more common than other food types Our first principle then generated by the model is Whether a food item is taken depends on the abundances of better items not on its own abundance see answer to Homework problem 1 Problem 2 The second exercise illustrates the second principle As food density increases overall animals should become more selective In this problem we raised the density of all food types proportionately pi s stay the same search time T5 decreases when prey are abundant it takes less time to find the next one Under these conditions the best item is common enough that the forager can maximize its energytime by eating only that best item it drops the second best item from the diet even though it was acceptable before These two predictions nicely illustrate the value of a simplifying model This model yielded counterintuitive predictions Animals should quotselectquot items for the diet which means that they reject some items even when that item is the most common that the forager encounters and even when that item was acceptable before Ecologists at the time relied on their quotcommon sensequot that animals feed totally quotopportunisticallyquot that is animals fed on any suitable prey that they encountered when they encountered it The trouble was their quotcommon sensequot was wrong That is what science is the formalization of quotcommon sensequot into testable hypotheses and the rejection of hypotheses that fail the test Theory and modeling is a powerful way to formalize quotcommon sense quot We will see numerous examples of this scientific process in EVE 101 2002 Catherine A Toft EVEl 01 Lecture 4 Page 10 Now for the tests D Tests of the model Most of the tests of simple OFT are necessarily done in the laboratory where conditions can be carefully controlled and factors varied one by one a Great tits This small passerine bird occurs in England amp Europe The quottitsquot are the same birds we call quotchickadees quot and are closely related to the quottitmicequot Krebs and his colleagues took this intelligent bird and taught individuals to take food off of conveyor belts This is the same species that learned to take the caps off of milk bottles and drink all the cream This learned trait spread culturally until so many great tits knew how to do this they had to redesign milk bottle tops The birds foraged on larger and smaller meal worms on the conveyor belt the conveyor belt changed speed to simulate the quotdensityquot of prey ie the search time The large and small meal worms were put randomly on the conveyor belt so the bird did not know which was coming next thus simulating random search for the purposes of testing the simple model Their experiments were set up to test both predictions 1 and 2 but their experiments did a better job at testing prediction 2 than prediction 1 The birds made choices that conformed very well to predictions of OPT but not perfectly as you see refer to lecture transparency in particular the birds got more selective when density of both prey types increased faster conveyor belt However in all experiments the birds still took a small number of lower ranked prey even when the model predicted they should always reject the lower ranked prey they ate some small mealworms even when large mealworms were relatively more common Keep this quotmistakequot in mind as we continue b Blue gill sunfish if you don39t remember the lecture transparencies of the first two examples then concentrate on this one discussed iin your text on p 150 Figure 624 Werner Hall and Mittlebach set up experiments in the lab and observations in the quotfieldquot on wild bluegill sunfish Bluegills eat aquatic invertebrates such as daphnia copepods and insects which come in a range of sizes They calcuated the et of each of the prey types which was mostly dependent on the size of the prey energy content increases faster than handling time with increasing prey size Then they too manipulated total prey density and relative density of the different prey types testing mainly prediction 2 and to some extent prediction 1 Again bluegill sunfish fit the predictions of the model pretty well but not perfectly The deviation is toward including slightly more suboptimal prey in the diet than the simple OFT would predict This was true both in the controlled laboratory experiments and in the field observations of wild bluegills c Trout This example is presented a little differently The trout were starved for a consistent 2002 Catherine A Toft EVEI 01 Lecture 4 Page 11 amount of time eating brine shrimp is about the same as starving and then offered a mixture of large and small trout chow pellets The experimenters calculated the maximum energy gain in foraging if the fish foraged optimally rejecting small pellets to search for larger pellets and they calculated the energy gain if the trout ate the pellets in the same proportions as they encountered them ie if they foraged randomly The trout did not perform perfectly either although they eventually matched foraging predictions pretty well refer to lecture transparencyThis example shows that it took trout some time to achieve the optimal predicted diet they did not do this instantly Eventually their observed diet was close to optimal but slightly below it in energy gain slightly suboptimal I could give you any number of examples and they all conform to these Vertebrate predators all match OFT predictions well but not perfectly Your textbook author Molles calls the match between observed and predicted quotuncannyquot so he39s pretty happy with it However the tendency to accept a few lower ranked prey when they shouldn39t partial preference for low ranked prey seems to prevail in so many experiments perhaps we as scientists should not ignore it Question Is this lack of exact fit just part of experimental slop or is there some biological significance to it Possibilities are 39 1 OFT is quotwrongquot However fits are too close to be totally wrong Maybe there needs to be some fine tuning 39 2 Let39s examine some of the assumptions of the model Important ones are 39 a forager can assess the value of food upon encounter 39 b forager knows the array of different foods available 39 c forager searches randomly The first two assumptions expect the real world to be perfect which it s not Maybe a forager has encountered a food item before and recognizes and accurately remembers its et value Or more likely the real world is unpredictable Novel food items are often presented previously encountered food items may change in value Foragers migrate through different habitats seasons change and chance events occur The forager might therefore make mistakes In this instance we have overestimated the forager The third assumption underestimates the forager in that we assume that the forager does not have a sophisticated ability to search However there are three important reasons why it benefits an animal to behave non optimally as predicted by our simple model in the short run 39 1 Foragers continually explore and test Sampling Maybe that food item was of low quality before but what if it changes Fruit ripens prey becomes gravid full of eggs or whatever It pays to take some risk of loss of energy or time to gamble on a better gain 2002 Catherine A Toft EVE101 Lecture 4 Page 12 Foragers are not omnisicent like the model assumes Exploring and testing may result in more profitable foraging in a time frame somewhat longer than a single foraging bout 39 2 Search image amp prey switching Many visual vertebrate predators develop a search image When one food type is abundant and if it pays in et to eat that food type then the forager focuses on that one food type It continues to eat that food type preferentially that is in higher proportions than found in the environment relative to other acceptable foods and it may not even notice other acceptable food types while it is foraging on that one Eventually when the forager concentrates only on that food type it will be depleted When the density of that food type falls below a threshold density then the predator switches to the new food It now seems to avoid the original food eating it in lower proportions than found in the environment GRAPHS of search imageprey switching Fig 621 Type 3 One food type might take an entirely different mode of searching than another or present a totally different image And once spotted it may require an entirely different pursuit and handling mode The forager can decrease search and handling time by specializing on that type of food that is most abundant that is even if the prey is abundant the forager is choosing it disproportionately often more often that it would if it look prey at random Believe me this works I have personally tested this idea many times in trying to collect insects as part of my field work in the desert If I39m trying to census two different types it is often easier to census one type and then census the other type 39 3 Finally the forager may have constraints not built into the simple framework of energy and time Many foragers are trying to balance protein and carbohydrates amp lipids or are trying to minimize undigestible material e g cellulose or are trying to get micronutrients eg leaf eaters are often sodium limited all organisms need vitamins minerals and trace elements that might not be found in the most energy rich food Summary of OFT OFT is not the only model framework for predicting diet Its appeal is that it is simple and yet highly predictive However more complex models do a better job of predicting diets although the problem is that the models are more complex and harder to test Two examples of more complex types of models are linear programming and dynamic modeling both of which you could learn about in a more advanced course than EVE 101 OFT provides good but not perfect predictions about how real animals forage Tests of the model deviate in ways that we expect by replacing the unrealistically simplistic assumptions 2002 Catherine A Toft EVEl 01 Lecture 4 Page 13 39 1 real animals don39t have perfect knowledge of the environment 39 2 real environments are changing and variable and often unpredictable 39 3 real animals don t search randomly rather evolution has fine tuned their searching abilities to make search more efficient more benefitless cost 111 Types of foragers A Background Beyond the single foraging bout Everything under OFT occurs in ecological and behavioral time explicity during a single bout of foraging We have aleady seen how the forager might be maximizing et over a longer period than that such as its lifetime In particular there is explicitly NO evolution incorporated in the simple model which would view foraging over more than one lifetime generation The variables in the simple model are considered fixed properties of either the prey type or the forager and during the single foraging bout they are assumed not to change However ei and ti are properties the prey and TS and CS are properties of the forager predator that might be determined through evolution In particular the interaction between the forager and its prey should be subject to natural selection 39 1 Evolution might make a forager39s senses better so that it can detect food items faster or from a greater distance and so reduce TS and similarly the food item would benefit from being harder to detect so that evolution should thereby increase T5 2 Evolution might adjust morphology and physiology to reduce the search costs in energy CS and likewise evolution on the prey item might make it harder to detect increasing CS 3 Evolution might also adjust the forager s food gathering or capturing morphology to reduce handling time ti and similarly evolution of the prey species should be to make the prey harder to pursue and digest increasing ti 39 4 A forager39s digestive physiology might change to allow it to get more energy ei from eating a type of food and likewise natural selection on the prey could make this energy harder for forager to extract thus causing the forager to ignore that prey when it is encountered So many of the parameters of the OFT models might evolve by natural selection to increase a forager39s net gain in foraging and evolution in the prey might counter this evolutionary change in the forager Plants evolve defenses that reduce the value of food for foragers Animal prey evolve mechanisms to detect the forager sooner or at farther distances and TS goes back up 2002 Catherine A Toft EVEl 01 Lecture 4 Page 14 Animals might have anti predator defenses such as stings morphology and other such to increase handling time and therefore decrease et for the forager When forager and the food predator and prey etc evolve in response to selection pressure from the other we call that coevolution Your book covers these coevolutionary aspects of predator prey coevolution in the chapters on specific quotpredator preyquot systems Molles Ch 6 139 144 Ch 14 pp 321 334 39 Plantherbivore systems 39 Herbivorecarnivore systems 39 Parasitehost systems Take some of these examples of free living foragers ie herbivores or carnivores and speculate on how these defenses and counterdefenses might change the terms of the simple OFT model Red Queen Effect The Red Queen in Alice and Wonderland had to keep running faster and faster to stay in the same place Ecologists refer to coevolution between forager and food predator and prey as the Red Queen effect As evolution in one species improves foraging evolution in the other species improves the ability to escape or discourage the foragers so the forager and food species stay in the same quotplacequot Ecologists also refer to this coevolution as an quotarm s racequot making the analogy to the Cold War in which nuclear powers keep having to increase their arsenals to keep up with the other nation which may then try to get a little better to be sure of winning in an actual conflict The princple is the same as in coevolution Finally keep this thought in mind such predator prey coevolution leads inevitably to specialimtion as foragers get better and better at certain things and prey get better and better at escaping predators Can you see why Recall the principle of allocation We also could think of the common saying quotA jack of all trades is master of nonequot meaning that an organism cannot be very good at everything Instead we see what evolutionary biologists call quottrade offsquot in other words they trade off being not so good at one thing in order to be good at another Or they give up one thing in order to get another because they can39t quothave it all quot We can relate to this principle all the time in our daily lives 2002 Catherine A Toft EVE101 Lecture 4 Page 15 B Foraging quotmodesquot Because of this coevolution often suites of characteristics go together necessarily to quotbalancequot what we might call a foraging mode First as a forager gets better and better at getting certain kinds of food the forager loses its ability to forage on other types Second we will see that there are consequences to adopting a certain mode of foraging We also can call these quotmodesquot strategies 1 Interspecies comparisons There are two broad categories of foraging mode in many predators that we see arising by convergent evolution over and over again primarily relevant to predators rather than herbivores 39 Actively searching forager widely foraging goes out and finds the food May be non mobile food such as plants or more often mobile food such as other animals 39 b SitandWait forager ambush waits for the food to come to it Mainly predators although you might put filter feeders in this category this is stretching things a bit HANDOUT from lecture Most interesting is to compare a single limited taxon with both types of foragers Some things are obvious at first the sit and wait strategy has a minimum of search energy costs but it might have very large quotsearchquot time if we mean time to encounter prey For example bushmasters a large tropical snake wait for 3 to 4 weeks between meals and then eat 1 deer In contrast garter snakes actively search for small fish and invertebrates Their prey are small but common so they eat many meals per day Can you think of other comparisons within a taxonomic group Searching foragers have much higher quotenergyquot overhead in process of searching However they are less at the mercy of environmental unpredictability Let39s look at some other correlates in your table on the lecture handout Eric Pianka and Ray Huey are lizard ecologists and I did the work Toft 1981 on tropical forest litter frogs for this table Examine the table on page 11 W 98 of your lecture handouts and list all the trade offs you see within each of the foraging modes or you can think of your favorite taxon and made a similar list comparing two different foraging modes Now let s examine the ecological details for each of the two foraging strategies and see whether one is better overall or not To do this it39s best to study two closely related species with different foraging strategies that occur at the same location Handout from Nagy Huey amp Bennett 1984 These scientists studied two lizards of the genus Eremias Lacertidae in the great Kalahari desert at around 30 S on the African continent In the period of study the actively foraging lizard did much better than the sit and wait lizard in simple et terms The costs of searching 2002 Catherine A Toft EVEl 01 Lecture 4 Page 16 were much higher for the searcher than the sit and wait of course but the searching got proportionately more prey and did much better in net energy gained It grew nearly twice as fast during the study So why aren t all lizards active searchers Perhaps the ambush lizard does better at other seasons Or maybe ambush lizard has a different life history strategy the topic of a coming up unit For example might grow more slowly but it might encounter less predation and live longer Or the ambush forager might use foods unavailable to the searcher and vice versa and therefore benefit from reduced competition a topic we will cover nearer to the end of the course 2 Within species 39 a Energy maximizers An individual with this strategy tries to get the most energy it possibly can from foraging so that it can put that energy into other uses growth eggs offspring parental care etc 39 b Foraging time minimizers An individual with this strategy tries to get just the energy it needs in the least amount of time in order to have time left over for other activities primarily territoriality and mating In most species typically females are energy maximizers because by definition females produce the expensive gametes EGGS or otherwise care of offspring such as live birth A female39s fitness is typically highest therefore by investing relatively much in each offspring Females thus need a great deal of energy to maximize their fitness to produce large eggs to give birth to well developed young to invest in feeding and care of the young By definition males produce small inexpensive gametes SPERM Because the gametes are small and cheap males can produce lots of these gametes and typically they spend a lot of time spreading these gametes around Therefore males are typically foraging time minimizers it is thought in order to spend more time in activities leading to mating Is this simple dichotomy which comes from the fundamental property of anisogamy true This topic leads us directly into the next unit where we will look at these notions in more detail less from a foraging point of view However most tests of this dichotomy reveal that a surprising number of males are ALSO energy maximizers Why Example of Belovsky s study of moose Belovsky did one of the first extensive tests of OPT using the technique known as linear programming a branch of linear algebra Like most herbivores moose need to minimize cellulose and make a special effort to get sodium in otherwise low quality food Linear algebra is a field of mathematics that allows you to solve several related equations simultaneously A scientist need to take not only energy into account but also sodium and cellulose linear algebra provides the tools to do this In his study of moose Belovsky found that pregnant female moose are definitely energy maximizers as he predicted He predicted that nonpregnant females would not be energy 2002 Catherine A Toft EVEl 01 Lecture 4 Page 17 maximizers but he was wrong because nonpregnant females nevertheless store up energy for pregnancy the following year His biggest surprise was that male moose were also energy maximizers It turns out that competition among male moose for females is intense and the biggest baddest male moose gets most matings In order for a young male reach his highest fitness potential as quickly as possible he needs to maximize his growth rate and reach a larger size than female moose and as large a size as possible So male moose are energy maximizers too Calling male frogs might be considered foraging time minimizers during the mating season often males do not eat at all during the few weeks that mating takes place Summary Likely both sexes are energy maximizers during much of their lives but males are most likely to be foraging time minimizers during breeding season Nonetheless our biases somehow lead us to underestimate the amount of energy a male needs to maximize his reproductive success 2002 Catherine A Toft mm HAW p 1 m m 7m Duls yrwbpudznl papm mnngwth Mallzs Figs nan pp 259752 13 377 pp sum 1 Disnydzpuldznlhlm mumwbatnnks a Nam ms xmxnzmsnm K Papulaunn Density N a u Wrmm mum nu nimneu a W W ms xmxnsvnsnw Ths pamm Dr W at lags papula an vah x mm as mm mm a e 1 mu m slap at ths plm at pmapna papulaonn yuwth agam papula an dznsxty 1 7 mw mu M 11 am mam Whmpmmmwmpucapm an mm mm T mstantammls m at nuclease EVE 101 7 W08 Lectures 10711 Handoutp 1 Predator prey interactions Verbal explanation of model Trophic Level 1 Lower trophic level LTL prey plant host Rate of growth 93113312131231 m magma DI funntmml reap 3 Number of 39339 PUP 1103 population 2 or capture rate predators Trophic Level 2 Upper trophic level UTL predator herbivore parasite 39numeriml lespume39 I Change 1113133 functional response x x Number of LU353 m T1113 11733611133 0139 PDPUl D 3 The conversan rate of predamrs 0f PDPUl UD 1 fund into offspring Volterra predator prey model Molles Ch 143 pp 334 336 Don t let the differences in notation worry you dN Trophic level 1 Prey t rN aNP dP Trophlc level 2 Predator 3 caNP dP where number of individuals on trophic level 1 prey number of individuals on trophic level 2 predator r intrinsic instantaneous per capita rate of increase of prey births quotnaturalquot deaths quotUZ a capture rate of prey per predator functional response c conversion rate of prey into predator progeny a constant that relates the numerical response to the functional response d quotnaturalquot death rate of predator EVE 101 7 W08 Lectures 10711 Handoutp 2 Types of functional response Molles Figs 621 to 623 pp 147 8 Type I Linear predator never satiates Capture rate aN Capture rate Prey density N aN aNT Type II asymptotic handling time or predator satiates optional eg m or m Capture rate Prey density N Type III sigmoidal predator switches or prey have hiding places example formulae are all pretty complicated Capture rate f Prey density N m m 7m 1mm m H mm 111 cm I number at pny taken per pledamr per day mnmmsmm anm puntan mm qumn39uun mm ans Wm H pndamx p a a Wham pny w Mphnzuulymwlmzmpup zmnrgmmmhus Mallzs n 1m p 335 mm maum P Mum 11mime um p m 7 Wm mm mm hummus N N munm mum dznsny um EVE 101 7 W08 Lectures 10711 Handout p 4 Add prey densitydependence to the Volterra predatorprey model Prey familiar logistic with prey carrying capacity K dN N rN2 E rNl E aNP rN f aNP Predator same as before dP E caNP dP Phase plane analysis with ZPG isoclines amp equilibria N i M N 2 ac P a P n39a N 1 ac K Population behavior density II my 1 EVE 101 7 W08 Lectures 10711 Handoutp 5 Understanding phase plane trajectories The meaning of the Zero Population Growth Isoclines 1 Viewing the prey trajectories only P E I yreyde crease P In39a mm o a gt x 39 preyimrease N 11 Viewing predator trajectories only Pfdt I predaxur decrease lure deter increase N Eln39ElC EVE 101 7 W08 Lecture10711 Handout p 6 Understanding phase plane trajectories III Adding the prey and predator trajectories vectors dPr dt I P pre ydecrease hethde crease predator increase P The mm u pmyrimreaie I prerlaxor decrease 130th JJUJrEase W N dial To use this handout look first at the prey only trajectories and the predator only trajectories on the first page Convince yourself what the prey population will do above or below the prey zero population growth isocline prey population size at a steady state at the equilibrium number of predators Then use the same reasoning to see what the predator population will do above or below the predator ZPG isocline predator population size at a steady state at the equilibrium number of prey When you are satisfied that you understand each set of trajectories in isolation then add the two sets together The graph on this page illustrates how this is done The perpendicular prey and predator trajectories are vectors that are then added together to form a new intermediate trajectory Note the lengths of the vectors in this graph are only for illustration purposes and are not proportional to any rate of change The joint trajectories of prey and predator populations result in a cycle along any given set of trajectories each cycle depends on the exact values of the model parameters r a c and d Now practice translating the population trajectories on a phase to a graph of population sizes with time N and P Time avmmmx mexzeunmmmpx unwise cumpe nn and nichz Matimships Dmhping m mmmunhywidz pamnls m mumpmm cumpe nn Restqu mum mum mummmm nvzrbp inane dimum39nn Manes Ch 13 2 me 132 p Emiseeds Dfdxffelemsxzes membyaepemee ngmmdfmah The RUF m aqua512m m the perfmmanne curves that we amend m lemme 3 Resource Fm Lb equermyufuse Dfsume make unesuume vanabla ata gwem vane ummvarmue a Lb dls39ame betweenthe mean vahzs thhatmnhe vanable med byspemes 1 3rd spemee 2 lespechvely mum Bf Lb lesuume unluanunfmm n 12 are s39ardaxd dewanun a Lb ales ufuvedap between Lb Wu lesaume unhzanun fumqu Mth measures the uneasily uteumpenuemmme Overlap mule compenan em Nichz breath va mne madmltspemlu wme mane hmadIMgemszuu SP1 517 2 12 Sp z Resource EVE 101 7 W08 Lecture13714 Handout p 2 Species Packing Refer to handout page on Limiting Similarity Reasoning and Ecological Character Displacement Packing of species onto a resource spectrum is a metaphor illustrated by this graph am ahle re 311111 Resource Through either 1 an ecological process of invasion and extinction p 440 or 2 an evolutionary process of ecological character displacement Fig 108 p 236 eventually there will be as many species as the available resources allow in this community In other words as many species as possible will pack into the available resources until all resources are used by some species Any leftover resources are not enough to support a viable population of an additional species The next page will amplify this summary of the process of species packing You can refer back to this graph Smith s Field Ecology goes into this topic in more detail than your text See Smith s Chapter 22 if you d like more clarification EVE 101 7 W08 Lecture13714 Handout p 3 Limiting similarity reasoning Molles Ch 134 pp 310 12 Concept 1 RUF If resources are in short supply then species should compete for shared resources If a species niche can be represented meaningfully by a RUF below then we can estimate the intensity of competition as the degree of overlap between the RUF s of species 1 and species 2 represented by the competition coefficient 0L Q12 2 C21 In turn 1 is inversely proportional to dW which is the distance between the two means weighted by niche width In other words the smaller the distance between the two means the larger the overlap between RUF s That is the more similar the niches of two species the more they compete for limited shared resources Resource utilization function RUF and niche overlap in one dimension Practice changing d of two RUF s you draw on a separate piece of paper What happens to CL 1 Rescnn39ce Species packing and how communities get to be saturated Concept 2 Opposing forces of intra and interspecific competition Now let s take a community with only two species They are not very similar such as species 1 and 2 in the above graph If resources are limiting then there would be some pressure to use the unused part of the resource spectrum between species 1 and 2 This could happen in one of two ways Niche shifts or evolution could occur so that the niches of the two species covered more of the resource spectrum How the species niches end up depends on the relative strength of two opposing forces A Intraspecific competition could cause the d s to get closer andor the w s to get wider using up more of the unused resources between means of species 1 and 2 This process could occur by evolution as the fundamental niche changes or it could happen by changes in behavior or physiology as the former realized niche shifts to be closer to the fundamental niche B Interspecific competition Character displacement If evolution is changing the fundamental niche why wouldn t the two niches of species 1 and species 2 both converge as each species fundamental niche evolves to match the available resources This is what happens to the niches of the seed eating ground finches of the Galapagos Islands Molles pp 307 8 Brewer Fig 10 14 on Daphne and Crossman Islands where Geospizafortis and G juliginosa each occur in allopatry ie alone Instead interspecific competition exerts selection pressure EVE 101 7 W08 Lecture13714 Handout p 4 to reduce overlap and to increase the differences between means This is what happens on Albemarle Indefatigable Charles and Chatham Islands when G fortis and G Miginosa occur in sympatry ie together How does character displacement work Refer to the handout that shows the relationship between niches and morphology Concept 3 Species packing The above considers what happens between any two species sharing limited resources Now we can begin to fill up the available resources with as many species as can fit into the resource spectrum The idea is that as many species as possible will eventually occur together because if resources are limiting and some resources are still unused then yet another species will be able to invade and successfully establish a population in that area This process is sometimes called species packing from the metaphor that species pack themselves into a resource spectrum until all the available resources are used and all species are at carrying capacity This process of species packing stops when the community is saturated that is as many species as possible are there already If any additional species tries to invade this area then it or another species will go extinct by the process of competitive exclusion Process A Dispersal Read about this process in your book on pages 249 52 In every community in every habitat no matter where it is dispersing individuals are coming to an area from somewhere else We can think of this as a rain of propagules a propagule is any life stage that disperses such as seeds runners juveniles unmated males etc Any time an individual of a species not yet present in a community arrives we refer to this arrival as invasion After an individual or two or three arrives reproduction can begin If the population continues to increase in size even when individuals in that population are rare N is small and weak Allee effect then we consider that species to be established in an area Process B Invasion Can a population increase in size when it starts out small low density A variety of factors may work against a small population increasing in size We discussed the Allee effect already We also discussed the unstable coexistence scenario in the Lotka Volterra two species competition model Although that model was too simple it still provides some insight that a small population may not be able to increase in size when there is an established competitor already there Alternatively the invading species may be a superior competitor Not only can it increase when rare but it will soon take over and competitively exclude the species that was formerly present the first two outcomes of the Lotka Volterra model Process C Species turnover The two processes of invasion and extinction in particular by competitive exclusion should occur continually and simultaneously in any community Eventually if the community is saturated then the number of species will remain constant through time The actual species there may change however depending on how well any given species is adapted to that area and able to resist the invasion of close competitors When the number of species remains the same but the identities of the species changes with time we say that species turnover is taking place EVE 101 7 W08 Lecture13714 Handout p 5 The invasionextinction process can be illustrated by the following graph Population dynamics in ecological time invasionextinction processes When can species 2 invade successfully If d12 and d23 are not too small nor the oc s too large then there are unused resources and weak interspecific competition and this population should be able to increase in size Some ecologists predict that when invasionextinction occurs continually at saturation the dw between any two species will be constant over the resource spectrum Do you see why constant dw s ie uniform along the resource spectrum are predicted EVE 101 7 W08 Lecture 13714 Handout p 6 Ecological Character Displacement Molles Ch 134 pp 312 4 Ecological character displacement refers to the evolution of character traits of ecological importance The other type of character displacement is reproductive character displacement In either type of character displacement a given trait in two species evolves so that the species become more different from one another than they were before Thus the displacement refers to the evolution of differences between two species in a trait of ecological or reproductive importance The most common type of ecological character displacement is the evolution of differences in two competing species as a result of selection pressure from interspecific competition which lowers the fitness of individuals A trait in the two species evolves so that they use resources more differently thus reducing the intensity of interspecific competition compared to 1 an earlier time and 2 populations of the same two species in allopatry Ecological character displacement can occur under the following conditions Step 1 Two species share a common resource in short supply Their niches as measured by a RUF overlap over part of this spectrum of resources in short supply This overlap is proportional to the intensity of competition Eva301mm 23 For example let s consider the Darwin s finches Geospiza on the Galapagos Islands Fig 108 Individuals of the two species such as G fortis and G Miginosa on Charles and Chatham Islands all eat seeds but on average individuals of G fortis eat somewhat smaller seeds than those of G Miginosa The overlap in the sizes of seeds taken by the two species is the area designated by the symbol 0L the competition coefficient that in turn estimates the intensity of competition for seeds of certain sizes on this resource spectrum EVE 101 7 W08 Lecture 13714 Handout p 7 Step 2 The size of seeds that a finch can crack and handle efficiently with its beak is determined by the length and width of its beak Small seeds cannot be efficiently handled by a large relatively clumsy beak Conversely large seeds that are much harder to crack cannot be opened by a bird with a small beak Only the large powerful beaks can crack open these seeds So we see a relationship between the size of seeds used most commonly by any individual bird and the size of that bird s beak see also Fig 109 I 1 Seed Beak quot Step 3 When there is such a close correspondence between a morphological character and use of a resource AND when that resource is in short supply such that two species will be competing for it then we have the ideal conditions for character displacement to occur Interspecific competition for any shared resources will lower the fitness of individuals having beaks of intermediate size in the region of overlap indicated on this graph In this way selection will cause the means of this character to move apart so that the difference between means d increases as follows Chimera 139 Beak 39 Ilre tram ompetiicun The most powerful way to detect ecological character displacement in nature is to do comparisons of two species in allopatry and sympatry EVE 101 7 W08 Lecture 13714 Handout p 8 Step 4 Allopatricsympatric comparisons Molles Figure 1325 p 314 There is convincing evidence that ecological character displacement has evolved in species of the Geospiza finches in this example G fortis and G fulginosa Where they occur in allopatry each alone their beak morphology is intermediate compared to when they occur together We can assume that this intermediate morphology results in their utilization functions of seed sizes matching the available spectrum of seed sizes so that seeds of all sizes are used We would expect this pattern if seeds are in short supply The mean fitness of the single population would increase as the finches were able to use more and more of the seeds available regardless of what size they are So on two different islands G fortis and G juliginosa converge in their beak morphology In contrast when G fortis and G fuliginosa occur in sympatry interspecific competition occurs when they are able to consume seeds of the same size Interspecific competition lowers the fitness of individuals with beaks of intermediate size Beak morphologies of the two species diverge as ecological character displacement takes place This contrast in beak morphology in sympatry compared to allopatry is consistent with the hypothesis that seeds are in short supply and that both intraspecific and interspecific competition is occurring in this system We now know thanks to the work of Peter Grant Rosemary Grant Dolph Schluter and Trevor Price scientists who have worked on Geospiza in the Galapagos that seeds are indeed in short supply and that there is strong selection on birds depending on the sizes of their beaks as the available seeds vary in size from one year to the next This study is a classic work in evolutionary biology and ecology and you might be interested in the various books written about it Perhaps one of the most beautiful parts of this story is that Charles Darwin first proposed this hypothesis and it was the finches on the Galapagos Islands that crystallized his building theory of evolution by natural selection m m 7m ummz zmu mm mun1mm mum mmm um W mm Mallzs Ch 2 especxa y page N m 2n 1 thl ndunnhy humu ms 1 h esnmmea nm at snug pmdvced by h sun mm fans a any gven mm m mp curve 1 mm annual salar mm 1 Wu 12 mth m m lawn mm cums ale m Srmanth penads between spring and fa eqmmms and between fa and s eqnmmms Espec wely Whlch Srmnthcnrve s whlch accmdmgm m lab 1 anthz dlagan 3n u an an 1mm new smuhzm mnhzm hum th mmme 1 AW cncuhmn w mum FM Fig up 15 msam mx m ale ldtmzdpa ems armmmmm h39satmnsphzle as n dzpems m hsvxew we ale xaamgm acmwman Earth39s mmspm wnhu Humanism m sums am mmmzu mummy hemghlghnp m m Shamsme pamman lanamnl dammm m name H mm mm mmpmm cuculaunncells pamcula y mse sun lawn mm m Hadlzyce s Why m mm can and m Pam 21 3 In quotany man camplzx man dawn hue D Hadley Fem lceu l K mnzm gym EVE 101 7 W08 Lecture 2 Handout 2 II Atmospheric circulation by latitude B Horizontal circulation patterns Picture a sphere rotating rapidly our planet has a solid core with a thin very thin layer of gases held to the planet by its gravitational forces However as the planet rotates other forces are applied to the atmospheric gases Because any sphere is widest at the center or equator than it is at the poles the equatorial latitudes must travel farther than polar latitudes in each rotation What happens to the atmospheric gases at each latitude as a result of forces generated by the Earth s rotation Why In other words explain why there are easterly winds at some latitudes and westerly winds at others Molles Fig 25 p 17 Ho n1 Pole 392 n H West r39li Ht r the Tr39aulemms South as Tr39mlevmuiz39 II I39 quot 39 1 quotI f39 i I i II quot II I EnquotJ S I II 39I I39ll 39 3m 5s 5 I A I Mum r 12 an s 111 Further Reading Eric Pianka s Evolutionary Ecology has a nice summary of global meterology climate and vegetation in his Chapters 3 and 4 Also a text in physical geography such as Muller and Oberlander s Physical Geography Today goes into full explanations of these global patterns F AAAA Numb A 39T n Q EVE 101 7 W08 Lecture 2 Handout 3 Global patterns of climate and vegetation I Generalized precipitation zones by latitude This cartoon summarizes the zones of seasonal precipitation by latitude To understand these patterns refer to the figure of ideal vertical atmosphelic circulation cells Why are there high and low pressure areas Where they are Why is precipitation associated with low pressure on a global scale see Molles Fig 24a This figure is presented in detail in Pianka s Evolutiongy Ecology 5th edition Fig 39 p 51 Emmi NCI39TJ39 Falls1 at 14D U 3IZIquot an 13013 r 1 I I N 3 11113 111 SUJTJJTIEEI39 Sm hem mnter 4 I Northern aunt3139 hcni iem summer l L LESLII 39L39IJTJJTJE I 1 39113 2333 it summer ram 1T 39W llltE 1 511quot L39l39LtBI 113111 Later ram F FLmeI drought quot IJJ39J39JJ39JE 139 139quot 1g gt3 393 I p ump A unner mucume Lemeznmmo u Mum m wuld vgm nn and Hans Secuun 2 a Niches Thu caman n a hlghly nmph ed xchzmanc af Haldndge39x mum cxmmmn xchzmz ham an pammx af mmpenmle and pmpman hamfarmzd m nun nlevam m plan annual u man mmpuamle ml annual pnclpm an pamn alevapmmpua an and hummny Hadng s chsn39 m nn Smnh39x ma Etang mm m fully expandzd Haldndge xchzmz m Fig 6 an an page 59 and appllzx thl xchzmz m a map afthz wuth m mm mm afthz hank hmmm WNW g mu m E x5 c sumquot 5 Mun g 3 c hm a mum sac a 5 ff Lml P1 3323 mm 3 m 2 Wm WWW ac mm m mm mum WW Wm mummy Whitmhu s Mum I va y a mm m 3 n n Mdanmdumyzmw EVE 101 7 W08 Lecture 2 Handout 5 Climate and world vegetation Some terms you ll need for the quarter Vegetation A general term which can be used to 1 to refer to the plant species found at one location ora would be a synonym or 2 to describe the collective characteristics of the plants found at a location regardless of the particular species involved primarily characteristics describing their appearance and morphological 39 39 39 39 39 39 39 39 be implied as well 1e their 1 1 could Physiognomy In the most general sense the overall appearance of the vegetation such as from a distance At minimum the physiognomy includes some intuitive description of the life form or growth form such as we all recognize from common language mainly related to plant size Tree a plant that is typically tall as an adult and longlived There is a fortified woody trunk for support and a crown with the foliage leaves which are the primary photosynthetic surfaces Shrub a plant smaller than a tree but otherwise shares characteristics such as woody trunk and long life Herbs or herbaceous species Small plants and those without woody stems These include shortlived species such as annuals Some biologists separate the non grasses from the grasses the family Poaceae To simplify we ll include the grasses Other characteristics can be included in the term physiognomy such as whether the leaves are shed annually deciduous or not evergreen depending on the type of system an ecologist needs to describe Physiognomic vegetation types This phrase is perhaps unnecessarily complex given the simplicity of what it refers to terms recognizable in everyday language Forest Vegetation made up of trees close enough so that their crowns touch Savanna Trees widely separated with an herbaceous usually grassy understory Thicket or Scrub Shorter trees and shrubs but growing densely enough to touch Shrubland or shrub steppe Vegetation made up of shrubs often with an herbaceous understory Grassland Vegetation dominated by grasses but often including other herbaceous species Desert A desert is defined by having less than a certain amount of rainfall usually 25 cm or 10 inches and typically deserts have high potential evaporation because of high temperatures winds and other factors As a vegetation type deserts vary but mostly are sparse shrublands with some herbaceous understory of nearly all annual species Biome A general term meaning a particular physiognomic vegetation type and all the other species such as animals included This term implies a particular climate because of the close relationship between climate and vegetation type with an emphasis on terrestrial ecosystems Climate The annual profile or pattern of temperature and precipitation at one location Evapotranspiration The water lost by plants by evaporation and transpiration Most of the water lost by a plant is the obligatory loss during gas exchange through the stomata pores on the undersides of leaves By obligatory we mean that such loss cannot be prevented because the plant must respire and photosynthesize and exchange oxygen and carbon dioxide and because gas exchange must occur across a wet cell membrane For terrestrial organisms air must be saturated with water vapor in the structures used for gas exchange such as the stomatal chambers in plant leaves and lungs in animals To compute evapotranspiration or more commonly potential evapotranspiration we need measures of prevailing radiation average water vapor deficit windspeed and temperature So you see that an index of potential evapotranspiration is a good summary measure of climate F AAAA Numb A unner EVElOl Lecture 10 Part II Page 1 Lecture 10 outline Community Ecology Part II Part I I Introduction 39 A Overview 39 B Goal for the remainder of the course II Biodiversity 39 A Spatial patterns Latitudinal gradients Part II 39 B Temporal patterns Succession 39 C Stability and complexity in food webs 39 D Spatial and temporal patterns Island biogeography and species turnover III Applications 39 A World Biomes revisited 39 B Conservation planning revised March 3 2008 Molles 4 h edition pages Lecture 10 Community Ecology Part II II Biodiversity continued B Patterns in time Succession and disturbance Reading Molles Ch 20 Ch 16 1 Background De nitions and a history of ideas about succession Succession is the response of an ecological system to disturbance Thus succession occurs when the community at a given location has not reached an equilibrium By equilibrium we refer to a steady state of the community properties we listed in Part I including the identity of the species in the community and the characteristics of complexity numbers of species and links between them Succession can be thought of as the dynamics of resilience of communities of organisms that might occur in one location that is how a given community responds to a disturbance 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 2 We can therefore think of succession as changes in community structure with time Criteria for quotcommunity equilibriumquot are these properties at a steady state Certain properties are what we referred to as community structure 39 Number and identity of species 39 Species diversity number weighted by relative abundance 39 Connections among species links in food webs numbers and types Other characteristics can be thought of as functional properties of ecosystems 39 Soil characteristics including proportion of organic matter 39 Primary productivity 39 Flows of energy nitrogen carbon calcium sodium potassium etc Succession was traditionally thought of as a series of communities that replace one another with time until a final community is reached This final community is one that resists change in that the species present are not replaced by yet other species as occurred at earlier stages it is both resilient and resistant The predictable series of communities at one location is called a sere one point in time is referred to as a seral stage The final seral stage is called the climax community We might also think of succession more broadly as ecosystem developmen Because change of species composition and species diversity most often follows a regular predictable and repeatable pattern the analogy with ontogeny or embryonic development of a single organism is tempting but it has its limits We must be careful not to be uncritically teleological are there evolutionary forces that integrate components of ecosystems in the same sense as the component of an individual s one genotype body Ecologists throughout the past century have proposed this idea but it remains controversial Frederick Clements definitely thought that the ontogenetic model held and his pioneering ideas on the topic of succession re ect his view that succession is a totally deterministic highly predictable even inevitable endpoint of an ecosystem s response to disturbance All of the species in his concept of J t f quot J as an 39 A whole with the ecosystem function itself a property of these ecosystems as they change with time His main rival of the time Henry Gleason took nearly the opposite view which was that species in any community anywhere at any time are affected independently of one another by a multitude of varying environmental factors Both recognize the predictability of some seres but Gleason and later ecologists also recognized the variations in how a given type of community responds to disturbance depending on conditions Gleason s view is closest to that held by modern ecologistsif you include biotic factors in the environment In other words species interactions are important but whole ecosystems are not tightly coordinated units with all species selected for and integrated with an overriding 2008 Catherine A Toft EVEIOI Lecture 10 Part II Page 3 ecosystem quotfunctionquot For example while useful the concept of the sere becomes circular when ecologists begin to look for a predictable seral stage expecting there to be one when in fact communities grade into one another as time passes and species gradually turn over as individual species and not as coordinated communities of species see Molles question 8 page 478 also Fig 2024 In either case we seek to understand the mechanisms ie causes for replacement of certain species by others in time Investigating how communities change with time as we did with communities changing in space latitude is also a good way to understand the determinants of species diversityor even more broadly the determinants of community structure Your book covers the characteristics of communities that change with time in Ch 20 2 The role of disturbance in ecological systems A modern view of succession is one that examines the effect of disturbance on ecological systems and how they respond through time to those disturbances We can begin by separating the effects of major even catastrophic disturbances versus minor lesser disturbances We make the distinction between primary and secondary succession Primary succession occurs as life colonizes a substrate with no history of living organisms relevant to the communities that will exist there in the future New substrates are being created all the time by geological processes bare rocks are exposed during a landslide rocks quotweatherquot and decompose at the tops of mountains volcanoes erupt and dump ash lava and debris rivers ood areas to start new aquatic habitats39 in one place and deposit sediments to start a new terrestrial habitat in another lakes fill in with sediments from erosion or they might dry up with climate change ocean currents deposit sand to recreate new terrestrial habitats and so on The active surface of the Earth guarantees that new and quotbarequot substrates are formed continually Primary succession necessarily takes longer to proceed specifically at the start because by definition the conditions favorable to living organisms that will later occupy that site do not yet occur Secondary succession occurs when a place occupied by living things is disturbedby fire rain hurricanes agriculture etcto an earlier point in its ecological history By its nature a disturbance initiating secondary succession is thus less severe less disturbing than a disturbance initiating primary succession In secondary succession is there is a good substrate for plants to colonize a substrate already modified by living things soil formation and with propagules seeds etc already present Thus living things can colonize and or establish immediately in secondary succession 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 4 3 Examples California examples will be considered in Section 10 First let s consider some examples The classical example of succession is secondary succession from an quotold fieldquot to the temperate deciduous forest pp 4556 The classical example of primary succession is establishment of plants on coastlines such as on coastal dunes of lakes and oceans section handout pp 4750 Succession is more apparent l the more species there are ie the higher the alpha diversity and 2 the faster species turnover with time these two are related somewhat the more species there are the more change in species can occur with time and 3 the more change in communities that occurs from beginning to end Examples 39 l Breakdown of talus slopes near glaciers primary 39 2 Colonization of volcanic substrates such as lava ows or ash deposits primary 39 3 Colonization of landslides primary or secondary 4 Stabilization of sand dunes on the beach or lake shores ie the coastal dunes dunes usually primary 5 Colonization of rocky intertidal after sea level changes 6 Colonization of ood plains and sand bars in rivers usually primary 7 Recovery in streams after major ooding episodes 8 Filling in of lakes to create terrestrial habitat primary in the sense that no terrestrial propagules were present in the lake 39 9 Recovery of vegetation after fire SLIDES of some successional sequences Now that we have some examples rmly in mind let39s think about why such changes occur 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 5 4 Terms and concepts mechanisms of community change a We can summarize Clement s description of succession in modern ecological terms in these steps I l a new environment or substrate is formed nudation or genesis 2 invasion includes dispersal of propagules to the site establishment of individuals and populations increase when rare We can also call this colonization 3 turnover of earlier to later species Why can t populations that establish first replace themselves When do populations that dominate later arrive and begin to increase when rare 4 steady state equilibrium or stabilization Commonly this is called the climax community This stage brings up some complicated issues in ecology What is the nature of community equilibrium That is our next topic the relationship between community complexity and stability Smith on reserve has one excellent paragraph summarizing the best View I ve read of the process and endpoint of succession at the end of the section quotTime and direction in successionquot pp 6712 the last paragraph on page 672 quotWe could predictquot We can formalize these verbal descriptions of the stages of successsion in terms of the mathematical population models 39 what causes relatively predictable changes in the abiotic and biotic environments that predispose different populations species to ourish in that location at a given time Nigt0 Corollaries to this question are 39 what causes some populations to be able to invade a population s size can increase when individuals are rare dNdt gt0 when N goes to 0 at a particular time and not others what causes some populations to decline through time dNdt lt0 when at an earlier time the population was increasing that is why can t individuals in that population replace themselves what causes some populations to reach equilibrium dNdt 0 that is why can individuals in that population replace themselves when others couldn t You can see that discovering the mechanisms of succession involves much of what we have learned in the course Undoubtedly many factors are at work so no wonder succession has been so difficult to understand b We can divide the mechanisms of succession after the disturbance into two useful categories 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 6 39 allogenic Forces from outside the community ie the physical forces or quotabiotic factorsquot alter the environment to affect somehow the populations of species in the community Examples are weathering of parent material leaching erosion deposition of sediment etc autogenic Forces from within the community ie biotic factors the populations there alter the abiotic environment or biotic environment or both and affect the community ie one population can affect itself or other populations in the community either directly or through modifications of the abiotic environment Examples are soil building species interactions etc life histories Primary succession is dominated by allogenic forces in the beginning stages both primary and secondary successional seres involve a mixture of allogenic and autogenic mechanisms but later on autogenic mechanisms become increasingly important We can further subdivide autogenic mechanisms focusing on explaining the turnover of the earliest species to those coming in next Fig 2020 39 facilitation some species make the establishment of other species possible or at least easier inhibition some species make the establishmment of other species harder or even impossible tolerance species are all different and react to the environment individually species have no affect on one another These three mechanisms for autogenic succession lead to two possible patterns of species diversity through time allowing us to propose ways of testing for these mechanisms 39 oristic relay earlier populations don t overlap much with later populations and vice versa mechanisms primarily facilitation and inhibition models Otherwise we d expect the overlap of species to be much longer through time 39 initial oristic composition at one extreme species overlap in time is maximum all species are present at the start Relative abundances change because of individual species39s life histories mechanisms tolerance model 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 7 Summary Succession reaches no endpoint in an absolute sense However in a relative sense eventually many seres reach a state in which most species do replace themselves over generations particularly if there are no further disturbances and the climate doesn39t change We can probably refer to these as quotclimax communitiesquot but that is becoming dated quotjargonquot as ecologists take a longer view of succession In a given region with a given climate we still nd sufficient environmental variability so that seres can reach different endpoints depending on the local environment similarly to how we defined the spatial scale of quotbeta diversityquot Such situations have been called polyclimax A similar concept is that of climax pattern Some regions and their ecosystems are subject to more disturbance in particular to regular and predictable disturbance A good example is the California chaparral fire is to be expected every decade or two In such areas when the disturbance is prevented then the sere develops to a climax community in the traditional sense However when most areas are subject to frequent disturbance then we most often see earlier seral stages that in practice never develop to the climax community These stages are thereby named the subclimax If the disturbance is self generating we call it cyclic succession or shifting mosaic The process and rate of community change is entirely dependent on time scale On long enough time scales regional climate changesfor example the millennialong trends of the cyclic pluvial periods which bring on the ice ages or the centurylong trends of uctuating climate e g the quotlittle ice agequot of the 186039s which trapped the Donner party in the Sierra Nevada Obviously these longterm climate changes can bring on changes in communities and we see strong evidence for this See two examples in Molles 39 Ch 10 p 2345 Range Changes in Response to Climate Change Overlain on the much shorter time scale of secondary succession in temperate forests pp 4578 are the variable responses of tree species to longterm climate change from the last major glaciation Some species such as the Maple reached population equilibrium on a regional scale quickly while others such as the Hemlock did not until only about 2000 years ago which is much closer to the time scale of primary succession in that region So we might ask whether the species composition of a climax community is at an equilibrium yet or will it change further as a result of slow response of some species Hemlock to long term climate change Ch 213 quotOrigins of Landscape Structure and Changequot The Sonoran Desert example like that of succession on the shores of Mono Lake underscores how ecological processes in deserts occur on the same time scale as longterm climate change and landscape change When do you stop calling this community change quotsuccessionquot My own personal reply to this question is quotwho caresquot It39s best to examine the time scales and processes that you need to understand ecological patterns in any given setting 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 8 So it s important not to get bogged down in terminology Succession is the response of communities to disturbance We see changes in communities through time This change is partly deterministic which means that we can understand it and predict it if we know enough and it is partly stochastic in which case we can assign probabilities to the outcome again if we know enough Time is relative with some processes occurring on faster time scales than others The mechanisms of community change are numerous and not mutually exclusive So the best way to understand succession in a given location is to be openminded and try to learn the details of that system rather than to try to squeeze what is happening into preset de nitions and mutually exclusive models 5 Succession and life history We can relate concepts of successional change with generalizations about reproductive strategies and life history traits compare with the continuum of r and Kreproductive strategists Fill in more information yourself from your earlier lecture handout These generalizations are based on classic forest succession How well do they fit succession in other settings Early Middle Late species diversity 0 to low higher higher or lower reproductive strategies rselected Kselected Environment 39 harsh 39 bengin 39 physical 39 benign 39 harsh 39 biological Energy turnover high low Ecosystem property productivity efficiency 2008 Catherine A Toft EVElOl Lecture 10 Part II Page 9 C Community stability and complexity At the beginning of this lecture we summarized the properties of communities in two groups those properties having to do with the structure of communities which determine how complex a community and its relationships are and those properties having to do with the stability of a community or its response to disturbance In this section we will try to relate these two sets of properties In your book review the notions of complexity and stability quotThe Nature of Equilibrium The Nature and Sources of Disturbancequot Ch 164 the ideas about environmental complexity in Ch 16 the issues of food web stability and strong interactions in Ch 17 and ideas about community and ecosystem stability in Ch 20 p 470 Studies of just what we have been going over latitudinal gradients succession suggested to many ecologists that diverse ecosystems tended to be more stable This generalization was based on the following observations albeit observations that have since been modi ed or interpreted differently 39 l Latitudinal gradients with tropical communities apparently more stable and certainly more diverse cyclic and variable population dynamics are conspicuous at high latitude and not at low latitude 39 2The observation of successional stages with climax communities at equilibrium more diverse than earlier stages 3 Crop monocultures one species of crop cannot be maintained without heavy doses of herbicides and pesticides to kill colonizing species of plants and animals Thus a crop monoculture is clearly not at equilibrium Strong forces push it to a more complex state These simple observations have generated much controversies over the years The result was a growth industry of community theory using mostly simplifying models as we have done Experiments and field work on such an encompassing question has proven very difficult how do you manipulate a whole ecosystem with replicates and controls what kind of rigorous incisive data can you collect on hundreds of species at a time etc Let us review the development of this theory and attempts to test the hypotheses with model systems and see what ecologists have decided The original hypothesis could be stated explicitly specifying the direction of causality community complexity begets community stability cause complexity effect stability How do we test hypothesis Let s proceed to make the ideas more rigorous and testable First we must specify what is meant by quotcommunity complexity and quotcommunity stabilityquot 2008 Catherine A Toft EVEl 01 Lecture 10 Part II Page 10 Community complexity review 39 1 Number of species in a food web 39 2 Number of quotconnectionsquot also called quotconnectancequot 39 trophic vertical links 39 competition horizontal links 39 mutualism vertical or horizontal links 39 3 Strength of connections size of interaction coefficients such as a and c in the predatorprey interactions and a the competition coefficients or we didn t go over models of mutualism facultative weaker connection vs obligate specialist stronger connection mutualisms Stability It turns out that two very different things were meant by the word quotstabilityquot climatic stability constancy and predictability vs community stability Let s be explicit about community stability first We ve gotten a feel for that already These properties are referred to as structural stability We can think of these properties as the community39s reaction to disturbance 39 1 Resilience tendency to return to equilibrium and resistance tendency not to leave equilibrium if there is a disturbance Both properties imply that there is an equilibrium How fast do populations return to that equilibrium Does the equilibrium involve extinctions or coexistence Higher resilience and resistance means greater stability and vice versa 2 Variability in numbers through time Is there an equilibrium with constant numbers or with cycles Are there oscillations in the return to equilibrium What is the amplitude of any cycles or damping oscillations Less variability means greater stability and vice versa 39 3 Species deletions that is extinction This is also an equilibrium but one with fewer species Is there loss of species because the equilibrium is one with one or more species going extinction e g direct competitive exclusion Is there loss of species because the system has very low resilience or high variability in numbers causing extinctions by chance when you add environmental quotnoisequot Fewer species that go extinct after a disturbance means greater stability and vice versa 2008 Catherine A Toft EVEl 01 Lecture 10 Part II Page 11 Climatic stability These properties might be considered the major sources of disturbance 39 1 Climate is constant so that communities are disturbed less 39 2 Climate is predictable so that if there are disturbances at least the species in the community may be adapted to them and find them relatively less disturbing than unpredictable disturbances 3 Climate is benign This is a little different but in an intuitive sense a climate to which living things can more easily adapt is less disturbing to populations Let s cut right to the punchlines there are whole books written on this subject eg Stuart Pimm39s book on Food Webs Does community complexity beget community stability The answer now is quotit dependsquot But the general overall answer is that The more complex the food web the less structurally stable it is likely to be Structurally stable elements in food webs permit a higher complexity Climatic stability permits higher complexity fewer disturbances cause stability effect complexity A community is like a house of cards with species as the quotcardsquotthe more cards you stack up the more easily the entire quothousequot crumbles in the face of a disturbance This view is in contrast to the earlier view that species quotbuttressquot the system stability like supports in a suspension bridge as ecologists previously thought However this is just a very general answer Under some circumstances complexity can increase the stability of food webs What examples could you think of from material we covered in EVE 101 Here are some generalizations Everyone agrees all else equal that 39 1 Complexity puts an upper limit on the structural stability of food webs 39 2 Structural stability constrains the quotdesignquot of food webs 2008 Catherine A Toft EVEl 01 Lecture 10 PartII Page 12 Examples of some patterns 1 Food webs are not too complex The relative degree of connectance per species stays the same or decreases as the number of species in a web increases This is signi cant because the possible number of connections rises nonlinearly with increases in the number of species in a food web 2 Food chains are short At most there are 34 trophic levels There are two competiting hypotheses for this observation 39 Structural stability as above A longer food chain is not resilient and species may be lost after a disturbance Energy transfer Ecologists have hypothesized that this pattern is due to inef ciency of energy transfer up a food chain ie an energy quotpyramidquot so that top trophic levels eventually run out of enough energy to support a population However studies show that energy transfer constraints are less predictive than constraints from population stability in real food webs from Pimm s book 3 Omnivores are rare A true omnivore is one that eats from more than one trophic level simultaneously This type of connection in a web decreases the structural stability of the whole food web If you de ne omnivore this way you see that omnivores are disproportionately uncommon in food webs from Pimm39s book Consider human quotomnivoryquot in the kelp food web Disturbance of this food web by strong interactions and by exploiting multiple levels omnivory of the kelp food web caused enormous changes in the structure of the kelp food web recall the Section discussion 4 Scavengers are common Food webs with scavengers at the base are more stable than any other kind Ecosystem ecology con rms this prediction from a study of population theory ecosystem studies show that detritivores such as bacteria fungi mites and J are r 39 for J t as we know them This conclusion comes from principles not covered in our course Grand Conclusion Food webs are as complex as the environment permits That is the degree of CLIMATE STABILITY constancy predictability sets an upper limit on the degree of complexity of a food web Another way to view this is that complexity of ecological systems appears to increase despite decreasing structural stability I am reminded of Ian Malcolm s line in Jurassic Park and Lost Worlds quotLife will nd a way quot 2008 Catherine A Toft EVEl 01 Lecture 10 Part II Page 13 This new view accounts for the original observations well 39 1 You can still account for the complexity of tropical communities that are apparently more stable than communities at higher latitudes the constant predictable tropical climate reduces the degree of disturbance that tropical communities experience Thus food webs get as complex as the climate permits and that is pretty complex 39 2 And conversely you are more likely to nd simple communities in more variable environments because such environments are so full of disturbances to populations occurring there that complex communities do not persist 39 3 Crop monocultures are less complex than the climate permits in most agricultural regions However even these ideas are still being tested For example 39 1 Tropical communities are in fact quite resilient This property may have nothing to do with the complexity of communities but rather the higher productivity potential evapotranspiration possible at the equator 39 2 And conversely simple communities in desert and Arctic environments have very poor resilience for the opposite reason A single Motocross will produce damage in a desert that will last for a hundred or more years You can still see the 1849 wagon trails across the Death Valley oor Xeric climates low evapotranspiration and low primary productivity slow the inherent response times by orders of magnitude D Metapopulations Species area relationships and species turnover patterns in time and space Readings Chapters 21 and 22 1 Background This topic combines two related subjects quotmetapopulationsquot pp 4847 see Lecture 6 for a brief introduction to the metapopulation concept and quotislandquot biogeography or also quotspecies area relationshipsquot although these principles apply to any habitat with boundaries and all habitats have boundaries whether the habitats are surrounded by water or not The metapopulation concept centers on viewing one species at a time and the island biogeography concept is simply the manyspecies application of metapopulation concepts Here we introduce a general model quotequilibrium theory of island biogeographyquot pp 50810 In this class we will focus on how to predict the equilibrium number of species for an area ofa particular size Since this theory was first proposed in the 196039s it has been applied to current topics in conservation particularly that of habitat fragmentation by humans of course 2008 Catherine A Toft EVEI 01 Lecture 10 Part II Page 14 discussed in your book in Chapters 21 and 22 We will run out of time to cover these applications in lecture but if you are interested in ecology you should read these pages on your own 2 General model f0rmalizing the concepts of invasion and extinction Here we are imagining species quotrainingquot onto a location in the form of dispersing propagules just as we did when we talked about species packing These could be seeds larvae sexually reproductive adults and so on Once species colonize the area with a few propagules and start a population this population can either persist or go extinct eventually for all the reasons we39ve gone over in the class As result we want to consider the balance between immigration invasion and extinction rates and predict the NET number of species when these two forces reach a dynamic equilibrium We assume that species are immigrating and going extinct continually and so this dynamic equilibrium represents what is known as species turnover Note on terms invasion and immigration These are obviously related concepts In general population ecology immigration means the movement of individuals into one area of interest from another Perhaps a population of that species was already there When ecologists speak of invasion this process implies that a new population is established from the small number of individuals that immigrate Thus invasion is more speci c and includes more ecological criteria than immigration The use of the terms is not a 39big deal but rather keep in mind the difference in examining these processes at the level of the individual immigration or the level of the population invasion The original literature on island biogeography made immigration a complete synonym to invasion so keep that in mind as we cover this topic So we chart the rates of immigration and extinction as a function of the number of species already there Refer to your lecture handout p 456 and book Figs 2189 pp 508 Assumptions and fundamental properties of the model Imagine either an island or a habitat that is isolated from other habitats of the same type This place might be surrounded by water or it might be surrounded by habitat of a sufficiently different type that it is hostile to species in the first habitat Immigration and invasion Any area is subject to a quotrainquot of immigrating individuals of various species Therefore species come into the isolated habitat when individuals of that species immigrate from other places and establish a population Imagine a bare or empty place with no living things to start out with Any individuals that get there could establish a population of a new species on the island The more species there are the more likely it is that a population of that species is already there when new immigrant individuals arise So the rate of immigration invasion of NEW species falls off with the number of species already there There is no biology here yetjust the simple probability a species being quotnewquot as individuals arrive at random and establish a population The immigration rate will drop to zero when all the possible species that could be there are already there With no biology no interactions among 2008 Catherine A Toft EVE101 Lecture 10 Part II Page 15 species these are linear rates Extinction Here we see a similar principle but the opposite trend occurs with extinction rates The more species that are there the more species there are to go extinct for whatever reason Again without much biology just chance we assume linear rates Nonlinear rates add realism and provide a better absolute prediction ie the exact number of species at equilibrium but they do not change the qualitative predictions We could easily imagine that the more species that are there the harder it is for a few individuals of a new species to become established The most likely reason is that there is competition and limiting resources prevent a new species from a successful invasion of the island If so you would get concave rates If species facilitated later arriving species you might get convex rates Or competition among species could lead to competitive exclusion or predatorprey interactions etc So we might expect then rate of extinction to increase faster than linearly with increasing number ofspecies See text Figs 2189 pp 508 Predictions Equilibrium number of species and patterns thereof 39 Exact number of species at equilibrium No matter what the exact shape of the curves when immigration rates exactly equals extinction rates then that is the equilibrium number of species that occurs on the island ie as a steady state through time Keep in mind that it is the equilibrium number of species Moreover this is a dynamic equilibrium The identities of the species can change as new ones arrive and previous species there go extinction That is the species identities turn over while the total number of species stays the same This is how the term species turnover was derived and it returns to the dynamic nature of this particular equilibrium species turnover identity of species changes while the number of species stays the same new populations arise and established populations go extinct changing the identity of species on the island Relative number of species on the islands depending on 39 The size of the island or habitat patch The extinction rates might be expected to depend on the size of the habitat or the island The larger the area of the habitat or island the extinction rate will be lower and Vice versa Why Because the larger the area the larger the population in it and the less likely it is to go extinct Here we are postulating the effects of competition or some other regulatory factor For a given density fixed by whatever the more area the more total individuals there will be Fig 2113 Larger islands would equilibrate with more species than smaller islands 2008 Catherine A Toft EVEl 01 Lecture 10 Part II Page 16 39 The distance from a source of colonists The more isolated a habitat or island is the less likely individuals will be to arrive So places nearer to a source of immigrants will have more immigrants per unit time and so more new species arriving per unit time s Islands nearer to the source of colonists will have more species than farther islands 3 Current applications of island biogeographic theory a Species area relationships or SLOSS single large or several small reserves Theory of island biogeography attempts to predict the number of species at equilibrium which has the obvious application for how to design reserves to maximize biodiversity If we literally apply the basic predictions of this theory we come to the quick conclusion that we need the largest possible reserves or parks and that parks of a given size should be as near as possible to a source of immigrants such as a privately or publicly owned wilderness adjacent to park If we consider Yellowstone National Park the rst national park and one of the largest for example it is a huge park surrounded by large expanses of wilderness in both public National Forest Service and private handsor is it As habitat destruction continues at an exponential rate since the 1960 s the only wilderness fragments left are those within the boundaries of national parks In this country a national park is the highest possible level of protection from human intervention no forestry agriculture or grazing is allowed and since 1976 no new mining claims are allowed Note did you know that mining is the most legally protected activity in this country perhaps before life liberty and pursuit of happiness If you buy property in the US the right to mine the minerals on your property does not belong to you The right to mine in the national parks was protected since the inception of the US National Park Service Getting back to the ideas in this section Yellowstone National Park is not only large it contains within its borders a wide variety of habitats and ecosystems In fact we might expect that islandfragment size to be highly correlated with environmental heterogeneity leading to all the repercussions that we discussed above in the section on determinants of local diversity Let s consider some ecological consequences of separating these two issues area size and environmental heterogeneity 39 The larger the area of a single habitat type the larger the populations of species within this isolated area The larger the size of populations the less likely they are to go extinct for chance reasons Single large islands or fragments of a single habitat type and contiguous populations could be subject to natural extinction processes like competition exclusion extinction by predation or parasitism or obligate specialist mutualisms such as we discussed extensively in the section on twospecies interactions 2008 Catherine A Toft EVEI 01 Lecture 10 Part II Page 17 39 A single large reserveor an equal area of small reservesof several habitat types might have more species than a large reserve of one habitat type That is greater habitat complexity leads to higher diversity independent of size Several small reserves of all the same habitat type might allow a higher number of species if species compete and can t coexist Studies of real parks indeed show that numbers of species in many smaller parks add up to more species than fewer larger parks Quinn amp Harrison 1988 Are we always trying to manage for species number What about the identities of those species Some species can only exist in the largest unbroken expanses of habitat These include the top predators such as wolves and grizzly bears other wideranging species such as large parrots Or consider species that are adapted to the edge of habitat fragments as opposed to the centers the smaller the fragment the higher proportion of it is edge so that habitat fragmentation favors edge species We have to consider not only how many species but also which species we are managing Some of the assumptions of island biogeographic theory rest on immigration rates If parks are isolated by habitat through which no immigration at all takes place then we would expect species number to decrease gradually through time as some extinctions could be expected by chance alone This is a realistic concern in many settings certain sensitive species cannot disperse through dense populations of humans their urban centers highways agriculture and so on Recently a mountain lion was seen quite near Davis along the Putah Creek drainage Needless to say this sighting caused a big furor How are mountain lions supposed to disperse across the Central Valley What about small less vagile species of plants and invertebrates and so on Saving sensitive populations from extinction by some regular but perhaps small rate of immigration is now called the rescue effect b Deforestation Humans are really good at changing landscapes and in particular they are responsible for cutting down tracks of forests Consider this humans supposedly arose as a species in the savannas of Africa recall that a savanna is a biome in which there is a sparse canopy of trees without touching crowns and an understory of grassland In general wherever humans go they create savanna habitat In forested areas humans cut down trees and make clearings In grassland they plant trees and quotwindbrea quot around homesteads In deserts they water grass lawns And so on When humans of mainly European descent first invaded the large unbroken tracts of rainforest they began to chop down trees and create savanna landscapes Keep in mind that the much of this rainforest has been inhabited for over 10000 years by human populations that occupy the deep forest without clearing it Now the rainforest is significantly quotfragmentedquot See the dramatic gures in your book Molles Figs 231620 Such large scale changes even in uence climate because of the role of large trees and their evapotranspiration in the water cycles at low latitudes After deforestation the regional climate becomes hotter and drier Deforestation also occurs in 2008 Catherine A Toft EVEl 01 Lecture 10 Part II Page 18 the United States such as here in the western states and clearcut forestry methods IV Applications A World Biomes revisited In the last lecture we ll be seeing slides of all the world s biomes and talking about their characteristics and why they are the way that they are Don t miss it B Conservation planning Lecture handout summarizes the ecological principles that we have gone over that have something to say about the world s biodiversity what determines biodiversity and how to manage it as part of conservation planning Also some of the questions in the synthesis section for the nal exam ask you to begin to synthesize principles we39ve covered this quarter and applying them to ecological and environmental problems Here s the beginning of a summary you can add more to this list on your own Let me know what you come up with Also your book has some sections too on applications to conservation and management of wild populations 39 sheries and whaling management human population extinction of species quotbiological controlquot pest management habitat fragmentation minimum Viable populations 2008 Catherine A Toft 5mm Lecmrel perm R5219 Summary Biological Diversity Ecnlngjczl factnrs in uencing speeiau39nn cnwdslence and Extinctinn This summary will alluwyuutu 1 review ferme nal and zapp1y pnn ples 1e cunservauun and anagemem ufspecies and ecusystems Unit un individual 8511ng 1 humans Unit un singlersgecies yugula un guWLh 1 Allee effect reverse density depmdence with extinmun Lhreshuld 2 Inappmpnate repreaueuve strategies 1e rrselectedspecies zrepreadaptedtu 1 e v Unit un geguieuen interadmns Fredz nn including nerhiwry and parasitism 1 m Var r eye1es canbe levels Hmrstun smrur amp Slubudhn 19511 0211112 CathenneA Taft EVEI 01 Lecture 10 Part II Page 20 39 3 Predatorprey coevolution leads to specialization that might enhance the rate of speciation through simple allopatric r 39 quot or in 39 quot with 39 39 below Parasitehost coevolution may include the phenomenon of quotcospeciationquot 39 4 Predator or prey evolution not necessarily coevolution might lead to global extinctions as new innovations make older strategies of predator or prey obsolete new innovations may lead in turn to major quotadaptive radiationsquot of new species Competition 39 1 In ecological time competition leads to competitive exclusion This extinction might be local or global 39 2 In evolutionary time character displacement competitor coevolution can permit greater degrees of coexistence It might enhance the rate of speciation similarly to predatorprey coevolution because it leads to greater specialization Specialization in a sense leaves quotempty nichesquot that other specialists can ll Mutualism 39 1 Extremely specialized obligate mutualisms may have an extinction threshold 39 2 In ecological time mutualisms can enhance persistence or stability beyond what is possible without the mutualism thereby J the r 39 39 quotquot of 39 39 3 Highly specialized obligate mutualisms especially symbiotic ones may lead to quotcospeciationquot 4 Mutualistic coevolution leads to specialization which might predispose species toward speciation as above Unit on communities Intermediate disturbance hypothesis 39 l Predation or disturbance may be both too little or too great to permit the maximum possible species diversity Speciesarea relationships 39 2 Deforestation and fragmentation can result in a smaller equilibrial number of species through increased extinction and lower immigration but it also can keep competitors from ending up in the same fragment by chance and hence enhance regional coexistance Reserves could be designed on these principles HomelLecture notesl 2008 Catherine A Toft EVE 101 7 W08 Lecture 6 Handout p 1 Single species population growth I Geometric and exponential population growth Molles Figs 112 7 pp 255 9 Exponential population growth see text for the geometric equivalents r39 39m r I39Jru I39 Luzugarj m rut Pc39lflElaftbn Ifquot Pupil1313311 E 39 39 e r I1 I 1IL H quot r 41 g r IIIII H r I1 639 Rate of change in population size during a given time period t dN dN N dt r dtN r so r is the per capita per individual rate of growth in this population By definition r the per capita rate of population growth is constant that is it is independent of population density no matter how much population density changes Population size after a given time t solution to the differential equation Nt NO eIt Symbols N number of individuals in a certain area the population size or density N number of individuals at time t N0 number of individuals at the start time to t one time unit r 2 per capita birth rate b per capita death rate d r b d intrinsic rate of increase biotic potential This r can also be called rm or rmax e 2 base of the natural logarithms m m 7m mm HAW p z u Ingmpapula mnvath Mallzs Figs mu pp 25577 mummemmmmam gmnmpmm Vemusman lags equnan Addmmll 911nt K mcapamywh envuunmzm quotImam m amnnmaflemulces avauahle Inthls mndzl K canhe maugmmsm mamum nnmhemfmmvlduals am this mman can suppan xmx mmummmnsw m afmclease nu ruin man pmen alaxMaMhuslanpalamMu x1 scum m at nuclease gun h dznsny at m a mum nquot n dzmty hypathzocal Dr M mm passlhlz dznsxty hm m m m u papulaon mm m m u papula an dznsxty hypmhz cal ax m mm
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