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Speciation160-page2 - Adaptive Radiation as a Speciation...

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Methods of Speciation - 2 Allopatric (Geographic) Speciation When individuals are geographically, or physically, isolated gene flow is minimized. When there is little gene flow, changes that occur tend to isolate the gene pools. If something occurs that shuts off gene flow (some barrier), then differential adaptation, genetic drift or some other selection mechanism, accompanied with reproductive isolation can result in divergent selection. Squirrels at Grand Canyon Wrasses at Panama Isthmus Geographic (or Allopatric) Isolation barriers include: Rivers and changing river patterns Mountain ranges Lakes which dry up Volcanic eruptions Climatic changes, such as the ice ages Loss of land bridges
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Unformatted text preview: Adaptive Radiation as a Speciation Mechanism Patterns of speciation that involve adaptive radiation have been studied since Darwin's early work with the finch species on the Galapagos Islands. Darwin found fourteen species of similar birds on the islands, each feeding on separate food items, and each with a different beak shape. He speculated that the available food on the different islands "selected" for a specific beak shape. The distance between islands meant that only those birds in one area interbred, which resulted in the separation of species, and divergent evolution. Such multiple divergence is called adaptive radiation, and has been studied with many organisms....
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