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Ch53-Outline - Chapter 53 Community Ecology Lecture Outline...

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Chapter 53 Community Ecology Lecture Outline Overview: What Is a Community? A community is defined as an assemblage of species living close enough together for potential interaction. Communities differ in their species richness, the number of species they contain, and the relative abundance of different species. Concept 53.1 A community’s interactions include competition, predation, herbivory, symbiosis, and disease There are a number of possible interspecific interactions that link the species of a community. Interspecific interactions can be symbolized by the positive (+) or negative (?) effects of the interaction on the individual populations. 0 indicates that a population is not affected by the interaction. The effect of an interaction between two species may change as circumstances change. Interspecific competition can occur when species compete for a specific limiting resource. When two species compete for a resource, the result is detrimental to one or both species (?/?) Strong competition can lead to the local elimination of one of the two competing species, a process called competitive exclusion. The competitive exclusion principle states that two species with similar needs for the same limiting resources cannot coexist in the same place. The ecological niche is the sum total of a species’ use of abiotic and biotic resources in the environment. In the analogy stated by ecologist Eugene Odum, an organism’s habitat is its “address,” and the niche is the organism’s “profession.” For example, the niche of a tropical tree lizard includes the temperature range it tolerates, the size of branches it perches on, the time of day when it is active, and the kind of insects it eats. The competitive exclusion principle can be restated to say that two species cannot coexist in a community if their niches are identical. However, ecologically similar species can coexist in a community if their niches differ in one or more significant ways. A species’ fundamental niche is the niche potentially occupied by that species. The fundamental niche may differ from the realized niche, the niche a species actually occupies in a particular environment.
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When competition between two species with identical niches does not lead to the local extinction of either species, it is generally because evolution by natural selection results in modification of the resources used by one of the species. Resource partitioning is the differentiation of niches that enables two similar species to coexist in a community. Character displacement is the tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.
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