BSC 116 BSC 116
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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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