Ch 17- Community Ecology PDF

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Ch 17- Community Ecology Notes Key Properties of Communities

Interspecific Interactions in Communities

● community= group of species living close tg & interact ● diversity reflects different kinds of organisms that make up community ● Community diversity has 2 components: ○ 1. Species richness= total # of different species in community ○ 2. Relative abundance= proportion of community made up of diff species ● Ecological Niche= sum total of species’ use of biotic/abiotic resources in enviro ○ describes how species “fits” into community and ecosystem ● Keystone species= fill niches that play important roles in maintaining community structure ○ Presence determines which other species are present ○ If removed, composition of other species in community changes ○ have large influence on presence of numerous other species in community ● Interspecific interactions= interactions between diff ● species ○ May be positive (+), negative (-), or neutral (0) ● Competition (-,-)= when 2+ species in community rely on similar resources ○ May limit population growth of competing species ○ 2 species whose resource needs overlap closely cannot coexist in the same community

Interspecific Competition

● 2 possible outcomes of competition bt species w identical niches: ○ 1. Competitive Exclusion = 1 species will outcompete other & exclude from community ○ 2. Resource Partitioning = 1 or both species evolves to use diff resources ■ enables similar species to coexist in community ● In many situations, resource partitioning accompanied by character displacement: evolutionary divergence in 1 or both species that leads to partitioning of niche

Predation

● When organisms eat other organisms (+,-) ● Consumer= Predator ● Prey= Food species ○ Includes herbivory (consumption of plants by animal) ● Defenses to reduce predation: ○ Behavioral ○ Physical

● HIDING OR ESCAPING: some prey species hide, run, or both, effectively avoiding predation ○ variation of this comes from safety in numbers: many species travel in large groups to reduce predation risk (ex- school of fish) ● FIGHTING BACK: some prey species fight back against attacker, effectively avoiding predation ○ EX- fulmar seabird defends nest from attacks with vomiting aimed at intruder ● Aposematic coloration= animals w chem defenses often give brightly colored caution to predators Mimicry

● In some cases, prey species may gain protection by mimicking appearance of other species ● In Batesian mimicry= harmless species mimic harmful model ● In Müllerian mimicry= 2+ harmless species resemble each other ● Imagine 2 poisonous species: ○ Both are prey to common predator ○ Occasionally, predator will predate 1or other type of poisonous prey, and thereafter avoid it & organisms that look like it ● evolutionary advantage gained from similar appearance of 2 prey species: ○ predator that learns to avoid either species exhibiting Müllerian mimicry learns to avoid both

Predation

● Predators & prey act as strong selective forces for each other ○ Coevolution= When changes in 2 species genetic comps affect each other’s evolution ■ Predators evolve traits that allow them to serve as predators ■ Prey evolve traits that allow them to avoid predation; EX- egg deposits ● Some plants produce deposit on leaves that look like eggs of certain butterflies; butterflies prefer not to lay eggs on leaves that already have eggs

Symbiotic Relationships

● symbiotic relationship= interaction bt 2+ species that live tg in direct contact ● Parasitism= symbiotic relationship when 1organism benefits while other is harmed (+,-) ○ parasite obtains nutrients by living on/in host organism ● Mutualism= symbiosis that benefits both partners (+,+) ○ EX- Insect nectarivory ■ Insect gets fed, plants gets pollinated ■ Both win

○ EX 2- swamp aster flower pollinated by bumblebee that’s nourished by plant’s nectar ○ EX 3 (Devil’s Garden)- Ants that live in stems of Duroia trees use acid to prevent other plants from growing near tree, creating more space for home; tree benefits from ample space to grow ● Commensalism= 1 species benefits and other neither benefits or harmed (+,0) ○ EX- cattle feeds on insects stirred up by grazing buffalo; buffalo neither helped or harmed in interaction Parasites

● Parasites= predators that benefit from symbiotic relationship w hosts ● Plants can be parasites ● ECTOPARASITES= bedbug, live on host ● ENDOPARASITES= cause African sleeping sickness, live in host

Succession

● Communities can change/remain stable over time ● When communities disturbed, they gradually become reestablished ● process = succession ● Succession follows predictable sequence: ○ In primary succession, process begins in area where NO life/soil present (lava flows, volcanic islands, rock) ○ In secondary succession, process occurs in area where life/soil IS already present (abandoned farmland, after forest fire) ● Primary succession characterized by: ○ early colonizers ■ Good dispersers ■ Not good competitors ■ often opportunistic ○ begins after disturbance leaves area wo soil/life ● Secondary succession is characterized by: ○ later colonizers ■ Longer lived, larger species ■ Good competitors ■ often equilibrial ○ begins when disturbance opens up part of community to development of species previously outcompeted by other species in area...