11-30-11 Species & Speciation II - How new species arise and are maintained

11-30-11 Species & Speciation II - How new species arise and are maintained

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ZOL445 Evolution November 30, 2011 How do new species arise? 1. Genetic isolation 2. Divergence 3. Reproductive isolation Genetic isolation: Physical barrier (dispersal and vicariance) Genetic barrier (polyploidy and chromosomal changes) Divergence: Genetic drift o Founder effects and genetic drift will lead to genetic divergence between islands o Genetic drift and founder effect may only play a small role in genetic divergence: Only important when new populations are small (peripatric speciation) Alien species have been introduced onto small islands all over the world, but there are few observed changes in genotype and no speciation events. Natural selection o House sparrow size varies across North America and tends to be larger in colder regions (requires more fluffer to keep it warm). o Natural selection generates clines… o …even when environments are discrete.
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o Physical barriers will block migration and lead to genetic divergence through natural selection. o Note: clines can be linear, and circular, and overlapping… Ring species provide evidence for isolation by distance Example: Seagull species around the Arctic circle
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This note was uploaded on 12/21/2011 for the course ANP 203 taught by Professor Lewis during the Fall '11 term at UCSB.

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11-30-11 Species & Speciation II - How new species arise and are maintained

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