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Chapter 37 ~ Community and Ecosystems

Where’s 3?

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0011 0010 1010 1101 0001 0100 1011Community structure

• What is a community?• Community~ an assemblage of populations living close

enough together for potential interaction. Differ by..• Species richness (number of species) & abundance…….• Why are certain species found together?• Hypotheses:•Individualistic~ chance assemblage with similar abiotic

requirements •Interactive~ assemblage linked by mandatory biotic

interactions

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0011 0010 1010 1101 0001 0100 1011Interactions

• Interspecific (interactions between populations of different species within a community):

•Predation - including parasitism; may involve a keystone species/predator •Competition•Commensalism•Mutualism

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Predation defense• Cryptic (camouflage) coloration• Aposematic (warning) coloration• Mimicry~ superficial resemblance to

another species √ Batesian~ palatable mimics an

unpalatable species √ Mullerian~ 2 or more unpalatable, resemble each other

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0011 0010 1010 1101 0001 0100 1011Competition: a closer look

• Competitive Exclusion Principle

G.F. Gause - Russian2 species with similar needs for the same limiting resources cannot coexist in the same place

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Competition evidence• Resource partitioning~

sympatric species consume slightly different foods or use other resources in slightly different ways

• Character displacement~ sympatric species tend to diverge in those characteristics that overlap

Ex: Anolis lizard sp. perching sites in the Dominican Republic

Ex: Darwin’s finch beak size on the Galapagos Islands

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0011 0010 1010 1101 0001 0100 1011The Niche

• Ecological niche~ the sum total of an organism’s use of biotic and abiotic resources in its environment; its “ecological role”

• 2 species cannot coexist in a community if their niches are identical

Ex: Barnacle sp. on the coast of Scotland

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0011 0010 1010 1101 0001 0100 1011Succession

• Ecological succession~ transition in species composition over ecological time

• Primary~ begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier

• Secondary~ an existing community has been cleared by some disturbance that leaves the soil intact

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0011 0010 1010 1101 0001 0100 1011Trophic Structure

• Food chain shows transfer of energy up trophic levels.

• Food web is a network of interconnecting food chains.

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0011 0010 1010 1101 0001 0100 1011Species diversity

• Species diversity is composed of;species richness - number of different species in a community, and..relative abundance – number of species in a community.

• Keystone species exert control over community composition.

• http://www.youtube.com/watch?v=Ng6CNn6XnBg