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COMMUNITY ECOLOGY I. Community definitions and concepts a. A biological community is an assemblage of interacting species b. How are communities structured? i. Integrated hypothesis 1. Frederic Clements, 1874-1945 2. A community is an assemblage of closely liked species, locked into association by mandatory biotic interactions ii. Individualistic hypothesis 1. Henry Gleason, 1882-1972 2. Communities are loosely organized associations of independently distributed species with same abiotic requirements II. Interspecific interactions a. Competition i. Interspecific competition – different species compete for particular resource that is in short supply ii. Competitive exclusion 1. Lab experiments using Paramecium species a. Each species, when alone, shows logistic growth to carrying capacity b. When both species are present, one is driven to extinction by other 2. Competitive Exclusion Principle – two species competing for same limiting resources cannot coexist in same place iii. Ecological niche 1. Organism’s ecological role – the sum total of its biotic and abiotic interactions a. Fundamental niche – space organism COULD occupy, in absence of biotic interactions b. Realized niche – space organism actually occupies 2. Combine ecological niche & competitive exclusion principle -> two species cannot coexist in a community if their niches are identical iv. Resource partitioning 1. Differentiation of niches that enables similar species to coexist in community 2. i.e. insectivorous warblers; coexist because niches different v. Character displacement 1. Tendency for characters to be more divergent in sympatric populations than allopatric populations b. Predation i. Predators – animals that eat prey (usually animals) ii. 1. Claws, fangs, stingers, and poisons of predators 2. Crypsis, mimicry, shells, speed, acute senses of prey
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