Community Ecology PDF

Community Ecology -exponential continuous over lap discrete + rt...

Community Ecology -exponential continuous over lap discrete + rt add births No e to Ni = · X No -N = prev generation parential reproduce of increase gen · rate. r : intrinsic discrete + non. Overlap No : intial pop NN = X No - Np in pop size knichange. ↑ dies parental generation pup : > - x Births = new population I unit of time Introduction Community: a natural assemblages of different species, living and potentially interacting in an area In addition to intraspecific interactions (within the same species), also interspecific interactions (between species) Interactions in community ecology can be classified into three main categories: Competition Exploitation Positive  "Lose/ruse" ~ Competition (-/-) what cost/price is paid ↳ can be inter/intra (btwn same species Two or more species attempt to access the same (limited) resource Ex: food, shelter, territory mating/breeding , + nursery Results of competition:> - ex. burmese python Competitive exclusion: one species is out- competed and becomes locally extinct advantage can lead to speciation - taking Resource partitioning: species shift to avoid direct competition (specialize on a v specific food resource, change active times and/or behaviors) loss for winner of comp o expend energy o risk harm to self  Competition Con’t based on role in community r May what eat you result in changes to an organisms ecological niche (its role in the community, based on the location it is found and resources it provides/requires) Fundamental niche = where it should be based theory On Realized niche = where it actually is Character displacement occurs when closely related species (often resulting from sympatric speciation) diversify to avoid direct competition to avoid o will benefit organism compe speciation desert part diff. predators hunt at dife times (day/night)  & fundamental for niche rock Cenare barnacles realized niche smaller due to competition u/ Rock barnacles  not need to kill prey does Exploitation (+/-) Relationship where one member eats some or all of another massive cause of Includes predation, herbivory, and parasitism natural selection This relationship drives significant amounts of evolution via natural selection Although predators are often thought of as ‘bad’, there are larger- scale benefits to predation: analyzed - at a species level Removal of sick and weak individuals from the population Prevention of overpopulation/overexploitation of resources Predators good for maintaining healthy population arms race evolutionary predators/prey evolve adaptation my bettering  Predation Effects eaten being Evolutionary responses: avoid skunks Aposematic coloration (warning colors): ex. poison dart frog 7 opposite advertise bad taste/toxicity [do not eat] S Cryptic coloration (hiding colors): camouflage prey to hide them [can’t eat what you can’t see] ex. Chameleon , rabbits/hares avoid predation pred Use it to sheak up to prey Mimicry: resemble other species [look. look like - something toxic or dangerous] else Batesian: taste good, but look like something that tastes bad Mullerian: taste bad and look like something that also tastes bad mutually benefits both too many Bas- > increases risk to Mull. to be taken out  Herbivory - less intense intact i can roots back - grow “Predation lite”, feeding on plants (doesn’t need to be fatal to the plant) Results in stunning degree of natural selection due to evolutionary arms races (escalations of adaptations between interacting species) plants are : Chemical defenses (toxins, bitter compounds) stationary be Caffeine, strychnine, opiates must creative For Morphological defenses (physical/structural) defenses Thorns, spines, hairs, difficult to digest compounds can sured animal guts ex. silica in plants > - Parasitism - mistle to e - eat but keep nost alive Also “predation lite” but feeding while host is alive leeches Ectoparasites live outside ticks , the host - tick take worms Endoparasites live inside -> - worms hook worms the host Often leads to significant · can change behaviors physical adaptations, can require multiple hosts fit maturation to Stage complex life cycles with multiple hosts and transmission pathways S + ataranula nawk  lichen : food housing > - -fungi avoid coup - alge/cyano makes Food protection Positive Interactions (+/+ or +/0) Two types: Mutualism (+/+): benefits both species involved Often complement each other by providing services that the other cannot perform, such as digesting molecules, or collecting scarce resources Note that while each partner benefits, they do have some (lesser) costs as well Commensalism (+/0): benefits one member, ( does not harm or help the other · benefits are minimal neutral uncommon ( bird eats bugs jumping from movement from buffalo ; buttalo doesn't get affected Community Structure While all communities have multiple species and a range of ecological niches, the individual make up of each community varies; measured as diversity Species diversity: the variety of organisms making up the community, measured via two components: Species richness (# of different species) Relative abundance (proportions of different species) Shannon diversity index (H) is a measure of diversity (higher value = more diverse) Community Roles Regardless of diversity values, each member of a community has a role in maintaining the community structure; some are more important than others, but all can be connected by mapping out feeding relationships by food webs Food web = visual representation of potential feeding interactions between trophic levels Trophic level = grouping of organisms that access energy the same number of steps removed from original source (the sun*) How specific energy passes through trophic levels = food chain Trophic Levels Primary Producers: autotrophs (photosynthesizers) Primary Consumers: herbivores Secondary Consumers: predators that eat herbivores Tertiary Consumers: predators that eat secondary consumers Quaternary Consumers: predators that eat tertiary consumers Limits to Food Chain Length Due to inefficient transfer of energy between trophic levels, most communities cannot support more than quaternary consumers (5 steps) [energetic hypothesis] Why there are fewer carnivores than herbivores Visualized as comparison of biomass (total mass of all organisms) Community Control Not all members are equally impactful; keystone species and ecosystem engineers can have disproportionate impacts due to roles in shaping & maintaining communities Depending on community complexity, some communities are more resilient (more diverse communities may tolerate invasive species or removals better than less diverse communities; more complex food webs may offer protection from trophic cascades) Disturbance & Succession Communities are not always static Disturbance: events that change communities by removing organisms &/or altering resource availability Fires, floods, droughts, climate change, human activities, tree falls, landslides Can be large or small scale Lead to ecological succession: recovery process after a disturbance event Primary succession = grow community ‘from scratch’ (no soil/life; uncommon) Secondary succession = re-grow community (soil/some life recovers; common) Disturbance Isn’t Necessarily Bad! Intermediate disturbance hypothesis argues that mild to moderate disturbances lead to more diversity Too much disturbance = too challenging Too little disturbance = too established (competitive exclusion) Other Factors Influencing Communities Humans (obviously) Biomes/Productivity More diverse, productive communities found near the equator (mostly); more food sources = more species Size Larger areas = more complex communities with more regions and species Isolation Island equilibrium model: island size, isolation control immigration and extinction rates (to a point) Pathogens Can heavily impact community composition by modifying survival of certain species