Community Structure - Competition

Community Structure - Competition - Community Structure...

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Community Structure Part 1: Competition What determines which birds occur together in a given place? Or, What determines community structure ? The classic answer , based on “Gause’s Law”: Two species with identical ecological requirements cannot coexist in the same environment There is “limiting similarity” (“Hutchinsonian ratios”)
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How competition affects natural selection Frequency size seeds Bill size Next generation size The distribution of bill sizes flattens out because birds with large and small bills do best (more seeds available to them). Over time, the distribution of bill sizes will mirror the distribution of resources This is because individuals with large and small bills do better than individuals with intermediate-sized bills Curve flattens A hypothetical example with finches.
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A more realistic situation Frequency size seeds bills Next generation size Bill sizes get smaller Again, the curve shifts because of individual differences in fitness (not because the shift benefits the species in any way)
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Do we see these types of bill size shifts in nature? Crossbills in Europe - specialized on pine cones - large population cycles Parrot Common White-winged Range of common crossbill Pine Spruce larch Central Europe & Asia : Spruce abundant Scotland : Spruce absent; pine abundant. Bill is like parrot crossbill’s Isolated populations of common crossbills Himilayans : Larches abundant. Bill is like white-winged crossbill’s Bottom Line : Indeed, bill sizes shift to match resource type
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Do you see shifts in bill sizes in response to other species ?
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This document was uploaded on 08/24/2011.

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Community Structure - Competition - Community Structure...

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