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BSC 116

by: Ashley Bartolomeo
Ashley Bartolomeo
GPA 3.9

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Notes on ecology, population and communities
Principles Biology II
Professor Harris
Class Notes
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This 11 page Class Notes was uploaded by Ashley Bartolomeo on Sunday April 24, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Professor Harris in Spring 2016. Since its upload, it has received 12 views. For similar materials see Principles Biology II in Biological Sciences at University of Alabama - Tuscaloosa.

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Date Created: 04/24/16
Lecture 36 Introduction to Ecology Overview  Introduction to ecology  Distributions of species, globally and locally  Global distribution of biomes Ecology is the Study of How Organisms Interact with each other and their Environments  More complex mechanisms than we have been working with so far  Organisms interact with other organisms and their environments on various scales o Organisms o Populations: group of the individuals of the same species o Communities: groups of populations o Ecosystems: groups of communities o Landscapes: groups of ecosystems o The Earth: biosphere  Ecology and evolutionary biology o Evolutionary time: populations change to adapt to their environments o Ecological time: response of organisms, populations, etc. to their environments  Ecology and environmentalism o Not the same thing: science vs. advocacy o But, people that understand how the natural world works tend to be advocates Why are Species Distributed the way they are?  No species occurs everywhere o Even people o E.g., distribution of red kangaroo  Found in some places, not in others o Multiple factors determine distributions  Dispersal; kangaroos can’t swim or fly to Hawaii  Behavior; some animals will not fly over open water  Biotic: other living things; e.g., predators, prey, pathogens, competitors, etc.  Abiotic: physical factors; e.g., temperature, light, water, etc. Organisms often do not Occur Places even though they could survive there  To be somewhere, a species needs to have had the opportunity to get there o Dispersal: movement of individuals to new areas o Barriers to dispersal can explain species distributions o E.g., no kangaroos in North America, oceans  Ranges always changing: species might not be there yet o E.g., cattle egrets; not native to North America but have spread all over North America  May choose to avoid a livable habitat: psychological barrier, habitat selection o Avoid places they could live if forces to o E.g., antbirds wont fly across water (even short distances) Species’ Distributions are often Limited by other species  Other species = biotic factors  Species absent because other species is missing o Food, host, pollinator, etc.  Species absent because other species is present o Predator, parasite, competitor, etc.  E.g., herbivore can limit distribution of food species: sea urchins and kelp o Remove sea urchins (& other herbivores), kelp grows thick o Complex interactions: kelp can be hiding place for another species, and so on… Species’ Distribution Are Limited by their Physiological Tolerance  Physical/ chemical properties = abiotic factors o Temperature: too hot, too cold  Species adapted to one extreme, not well suited to another o Water: too wet, too dry  Salinity: osmotic issues o Sunlight: especially for photosynthetic organisms  UV from sun can do damage to animals too o Geology: the inorganic parts of the habitat  Minerals, pH, physical structure of land (e.g., rocks)  Earth is not homogeneous for abiotic factors o Leads to variation in biotic factors, etc. o Many abiotic factors can be summarized as climate: long-term prevailing weather conditions  Result of both global and local processes The shape, tilt, etc. of the Earth results in broad climate patterns  Surface curved: areas away from the equator get less intense sunlight  Pattern of heating/ evaporation: variation in precipitation  Axis of rotation tilted 23.5 : seasonal variation in sunlight  Rotation of the earth: circulation of air/ water currents There Are Local Variations in Climate  Proximity to water: moderate temperature and humidity o Coastal areas moister than inland of same latitude o Air changes temperature fast than water  E.g., hot day, draws cool air from lake  Mountains have several effects o Shadow to sunlight  E.g., northern hemisphere, south facing slopes warmer, drier o Altitude & temperature: every 1000 m equivalent to 880 km in latitude (6 C)  E.g., northern species can extend south at high altitude o “Rain shadow”: warm air passing mountains cools and drops moisture  E.g., deserts on the leeward side of mountains  Tilt of the earth results in predictable seasonality: leads to variation in day length, sunlight, temperature o Away from the equator, leads to temporal variation o Closer to equator: dry season (cool), wet season (warm) o Farther away: winter, spring, summer, fall There is Long term, global variation in climate  Some periods are warmer/ cooler, wetter/ dried than others o E.g., we have already talked about Permian cooling and the rise of gymnosperms  Until 15-20,000 years ago: northern latitudes covered by glaciers o Species distributions changed after ice melted: each species migrated at own rate o E.g., eastern hemlock was 2500 years behind retreat  Species continue to move north (i.e., away from equator) as global climate continues to warm Biotic & Abiotic Factors Combine to Create Characteristic Biomes  Biomes: major habitat types, determined by both biotic and abiotic factors  Latitudinal variation in temperature, moisture, etc. leads to latitudinal variation in animals & plants o Characterized by plant types especially o Species composition variations across, among biomes o Ecotones: areas of transition between biomes  Disturbance leads to community variation, patchiness o E.g., fire, hurricanes Aquatic Biomes Are Characterized by Salinity and Depth  About 75% of Earth’s surface aquatic: several aquatic biomes o Freshwater (< 0.1%) vs marine (3%) o Pelagic (open water) vs. benthic (bottom)  Most photosynthesis occurs near the surface o Light filtered out quickly: photic vs. aphotic Lecture 37 Populations Overview  Population ecology and dynamics o Variation in life histories o Exponential growth o Logistic growth o Density dependence versus independence o Metapopulations On a Finer Scale Than Biomes, Populations  Population: conspecific (same species) individuals occurring in a particular area o Live in same environment o Use same resources o Interact/ breed with each other  Populations are dynamic: changing o Gain individuals from births o Gain individuals from immigration (arriving) o Lose individuals from deaths o Lose individuals from emigration (leaving)  Use 3 characteristics to describe populations o Density: number of individuals per unit area (or volume)  Boundaries difficult to define (e.g., migration)  Various methods to estimate size/ density: e.g., mark- recapture method  Dispersion: pattern of spacing among individuals  Clumped: aggregated in patches; attracted to resources  Uniform: evenly spaced; repulsed by each other, as with territories  Random: independent of other individuals o Demographics: age and sex structure of the population Life Tables Are a Useful Way to Summarize Population Demography  Life table: age specific summaries of survival in population o Usually divided by sex  Constructed by following a single cohort from birth to death o Count the number still alive each year o Calculate death rates, life expectancy, etc. o E.g., Belding’s ground squirrels Survivorship Curves Are a Graphical Way to Express the Same Information  Survivorship curve: number alive plotted vs. each age o Y axis plotted on a long scale o E.g., Belding’s ground squirrel  Males tend not to live as long  Both have relatively constant death rates thru life  Species have characteristic survivorship curves, depending on life history: pattern of reproduction and survival o E.g., humans, whales, primates, elephants: low, constant death rate until late in life  Type 1, put energy into caring for a few offspring o E.g., oysters: high death rates early on, low for survivors  Type 3, put energy into producing many offspring without parental care o E.g., Belding’s ground squirrel: type 2  Survivorship is one factor that determines population size Reproductive Rates Are as Important as Death Rates  Reproductive table = fertility schedule o Generally, pay attention only to females in population o Follow reproductive output of cohort o Calculate average number female offspring  Varies with age  E.g., peaks with maturity, then declines  HUGE variation in life histories: results from trade offs; cost benefits of reproduction, etc. o Cost of reproduction: energy spent on offspring not spent on parent o Iteroparity = repeated reproduction: multiple reproductive periods  E.g., Belding’s ground squirrel  Favored in more predictable environments o Semelparity = “big band reproduction”: all reproduction concentrated in a single effort  E.g., agave = century plant  Favored in unpredictable environments: low probability of adult survival o Trade offs: can’t maximize all reproductive patterns at the same time  E.g., more offspring means smaller offspring with less care As Long As There Are More Births Than Deaths, A Population Will Grow  Change in population size = births during time internal + deaths during time interval o Ignore migration  N/ t = B – D  N/ t = bN – dN = (b – d)N o B, d: rate of births, deaths per capita  N/ t = rN o R= b- d, per capita rate of increase  dN/dt = rN o Expressed as the instantaneous rate (calculus)  R > 0, population grows, r < 0 population shrinks  The larger r, the faster the population grows o Produces characteristic J shaped curve  E.g., elephants in Kruger Park  Model of exponential population growth o Unrealistic in most circumstances Population Growth is Often Regulated by Feedback  Carrying capacity: number of individuals that a habitat can sustain o Limiting factors: energy, shelter, nutrients, territories, water, etc. o Can vary over time o Limiting resources can lower birth rate, raise death rate  Logistic population growth model: incorporates carrying capacity o dN/dt = rN((K – N)/K)  Where K = carrying capacity  E.g., when N (population size) is small, ((K – N)/K) is large  Characteristic S shaped curve  We can observe this in real populations o E.g., paramecium  Most populations don’t fit exactly o E.g., Daphnia will oscillate around K o Population “corrects” itself  Gives us a way to talk about life history trade offs o “K selection” for traits that are helpful at high densities  few relatively large offspring; Type 1 survivorship curve (humans) o “R selection” for traits that are helpful at low densities  Many relatively small offspring; Type 2 survivorship curve (marine fishes) Density Dependence is Ecological Feedback  When birth or death rates change with population size, they are density dependent o Population size regulated by feedback o Too small, grows; too large, shrinks  An equilibrium can be achieved when births equal deaths o Deviation from equilibrium can bring it back  Causes of density dependent regulation o Competition: finite resources shared among more individuals  Nutrients, energy, space, etc. o Disease: pathogens spread easier in crowded conditions o Predation: predator references may change at high prey numbers o Accumulation of wastes: large population may produce waste faster than it degrades o Intrinsic factors: physiological responses to crowding  E.g., stress hormones that lower reproductive rate, etc.  Change in population size from factors independent of density is density independent regulation o Weather events (i.e., drought, tornado, etc.) Population Size is Dynamic  Populations fluctuate over time o E.g., moose, wolves on Isle Royale  Result on biotic interactions  There can be long term cycles of associated populations o E.g., hare, lynx on 10-year cycle; why?  Resource limitation of hares in winter? Not supported by data  Predation: increase in hares leads to increase in lynx; overexploitation by predators leads to low prey densities Populations Vary in Space as Well as Time  We have been focusing on r, not migration o Populations connected by dispersal in a metapopulation (a population in a population)  Sources: positive population growth (r > 0), lots of emigration to sinks; organisms emigrate from sources  Sinks: negative population growth (r < 0), lots of immigration from sources required to maintain population; organisms immigrate to sinks o Population blink in and out over space and time in a mosaic o Habitat fragmentation can yield a metapopulation from what originally was a large continuous population o Some species occur naturally in a metapopulation structure  E.g., butterflies Lecture 38 Community Ecology Overview  Ecological communities o Types of species interaction 9predation, mutualism, competition, symbiosis, etc.) o Regulation of community structure Predator/ Prey Dynamics Are Examples of Community Interactions  Multiple ways in which species interact: symbiosis o Beneficial (+), negative (=), no effect (0)  Predation: +/­ one animal eats another o Predator adapted to locate, subdue prey o Prey adapted to hide, escape  Cryptic coloration = camouflage  Aposematic coloration: brightly colored, warning  Generally poisonous, venomous, etc.  Batesian mimicry: harmless resembling venomous, etc. animal  Mullerian mimicry: two venomous, etc. resembling each other  Herbivory: special case of predation; animal eats a plant/ alga o Plants adapted for defense  Physical structure likes spines, thorns, etc.  Chemical protections: poisons, nicotine, caffeine, spices, etc.  Parasitism: +/­ parasite lives off of host o Inverted size relationship, relative to predation o Directly or indirectly affects host survival and reproduction  Parasitoids: intermediate between parasites and predators o E.g., wasps laying their eggs on a caterpillar Many Species Have Positive (or Neutral) Interactions  Mutualism: +/+ both species benefit o N fixing bacteria on legume roots o Cellulose digesting protists in cow, termite guts o Flowering plants and insect pollinators  Commensalism: +/0 one benefits, other not affected o At least, not greatly affected o E.g., species that ride along or follow others to pick up leftovers, etc. Competition Results from Species Having OverLapping Niches  Competition: ­/­ species compete for resources needed for growth, reproduction, etc.  Niche: sum of the biotic and abiotic needs of a species; it’s place/ role in a habitat  Competition results from species having overlapping niches; various outcomes o Wide niche overlap leads to competitive exclusion  Weaker competitor eliminated from local area o Narrow niche overlap leads to resource partitioning  Species’ “realized niche” smaller than “fundamental niche”  Each species better adapted to a portion of the resources  E.g., two barnacle species competing for space o Can lead to character displacement: resource partitioning leads to  morphological differences  E.g., Galapagos finches in sympatry (living together) and allopatry (living  apart) Richness and Abundance Are Both Aspects of Community Diversity  What do we mean when we say one community is more diverse than another?  Species richness: number of different species  Relative abundance: proportion of individuals that belongs to each species  Two communities can have same richness but different structures o Various indices developed to summarize .  o E.g., Shannon Diversity Index,  H = Σ(p N  lnpN)   Trophic Structure is Another Aspect of Community Dynamics  Trophic structure: feeding relationships among species o Energy moves up from lower trophic levels o Food chain: producers (plants)  1 consumers (herbivores)  2 consumers  (carnivores)  Not really linear; better represented as food web o Multiple connections among levels o Species occur at multiple levels; e.g., omnivores that eat producers, 1 consumers  and 2 consumers  Most food webs have < 6 trophic levels; 2 hypotheses o Energetic hypothesis: inefficiency of energy transfer between levels, ca. 10%  Takes 100 kg of plants to support 10 kg of herbivore and 1 kg of carnivore o Dynamic stability hypothesis: longer chains less stable than shorter  Fluctuations at bottom magnified in levels above  Longer chain delays recovery of top after disturbance Sometimes a Few Species Have Especially Important Roles in a Community  Dominant species: most abundant or greatest biomass (total mass of entire population) o E.g., sugar maples forests: determine shade, soil composition, etc., and thus other  species o Importance varies with community  E.g., krill in arctic community support many species  E.g., American chestnut disappeared, but other trees “stepped in”  Keystone species: key niches maintaining community structure; not necessarily  dominant o E.g., without starfish (Pisaster), mussels would take over o E.g., sea otters each sea urchins  Facilitators: “ecosystems engineers” o E.g., beavers create habitat Communities Have Both Top­Down & Bottom­Up Regulation  Three possible relationships between vegetation & herbivores o V  H: increase in V, increase in H o V  H: increase in H, decrease V o V H: both  Bottom­up model: V  H  C o Increasing V, increases H, which increases C, etc. o Taking C out should have no effect on V or H  Top­down model: V  H  C o Removing C, raises H, which lowers V o Increasing V should have no effect on H or C  The point: it is both, bottom­up and top­down  Understanding these processes allows for successful biomanipulation, intentionally  altering food web o E.g., removing fish (C) in Lake Vesijarvi to increase zooplankton (H) to decrease  algae (V) Species Richness is Maintained by Disturbance  We used to talk about the “balance of nature”, stable equilibrium, etc. o A community is a super organism, with species as its parts  Nonequilibrium model favored today o Community not a “thing” but a collection of “things” o Disturbance (storms, fires, etc.) keeps things in flux  Intermediate disturbance hypothesis: some disturbance increases species diversity o Low disturbance: dominant species exclude others o High disturbance: high stress; slow growing, slow colonizing species excluded o Intermediate disturbance: allows for a mix; creates patches of different habitats o E.g., fire burns down tall shade trees, other plants quickly re­colonize Within Communities, there is a Characteristic Pattern of Species Replacement  Ecological succession: first colonizers replaced by other species, which are replace by  other species o Each assemblage changes the conditions to give a competitive edge to the next  Primary succession: beginning without soil; e.g., after a volcanic eruption, glacier  Secondary succession: with soil; e.g., fire burns forest o Takes less time (don’t need weather rocks, create soils for plants, etc.) o E.g., succession in Glacier Bay, Alaska Broad­Scale Abiotic Factors Also Influence Community Structure  So far, we have mostly been considering biotic and local factors o Also larger scale influences  Larger areas have more species: seen in species­area curve o Larger area, more habitats, support more different species  Latitudinal gradient: more species closer to the equator; higher tropical diversity o Historical: poles recently glaciated o Climate: warmer, wetter, so higher productivity  Richness increases with evapotranspiration (evaporation + transpiration) Habitat Patches Can Be Thought of as Islands  Island equilibrium model: island size, distance away determine number of species o Island: good habitat surrounded by bad habitat o Equilibrium based upon species number o Shifted up for large islands, down for small o Shifted up for closer islands, down for farther


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