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Bio190-Communities

Bio190-Communities - Community Ecology Themes Species...

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Community Ecology - Themes Species Interactions Competition Predation & Herbivory Symbiosis & Pathogens Community Structure Trophic structure Roles of key species Bottom-up vs. Top-down controls Community Dynamics Disturbance —> Succession Models of Communities Communities - Introduction Community = an assemblage of species living in a habitat with potential interactions Communities attributes: Species interactions Structure & assembly Dynamics & disturbance responses Focus is on Biotic Forces —> Community Structure/Function (However, Abiotic forces involved too!) 1. Interspecific interactions among species of a community Interactions involve positive or negative affects on populations a. Competition Interspecific competition = different species attempt to use the same limited resources Intensity increases with: resource overlap, resource availability Result —> Competitive exclusion Competive Exclusion Principle : 2 species with similar needs for same limiting resources cannot coexist Gause studied competition in laboratory populations of Paramecium How do species avoid Competitive Exclusion? —> different habitats, or different niches The ecological niche is the sum total of an organism’s use of abiotic/biotic resources in the environment An organism’s niche is its role in the environment The competitive exclusion principle can be restated to say that two species cannot coexist in a community if their niches are identical Ecologically similar species can coexist in a community if there are one or more differences in
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their niches Connell’s experiment with barnacles demonstrates “Realized” Niches differ from “Fundamental” ( Fig. 53.2 ) Organisms can coexist in a community by evolving different niches (= Niche Partitioning) Also called resource partitioning ( Fig. 53.3 ) Character displacement = divergence of characteristics in sympatric populations of 2 species — > Niche displacement ( Fig. 53.4 ) Results from changes in gene frequencies b. Predation & Herbivory
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