lecture 12 new speciation and punc eq

The black bears distribution is now much more

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Unformatted text preview: n is now much more fragmented. Isolated bear populations are now free to adapt to their own particular environments. Clearly the environment in Florida is different from that in Mexico or Alaska or Newfoundland. Different environments are likely to favor different the adaptations. Is the black bear in the process of becoming separate species? Why or Why Not? Once two populations are reproductively isolated, they are free to follow different evolutionary paths. They are likely to differentiate for two reasons: 1) Different geographic regions are likely to have different selective pressures. Temperature, rainfall, predators and competitors are likely to differ between two areas 100's or 1,000's of kilometers apart. Thus, over time, the two populations will differentiate. 2) Even if the environments are not very different, the populations may differentiate because different mutations and genetic combinations occur by chance in each. Thus, selection will have different raw material to act upon in each population. What happens next? The fate of the populations depends upon time and factors related to their different environments. If the two populations are soon rejoined, they may not differ very much, and likely will become a single population again. Four steps lead to speciation 1. A single species is an interbreeding reproductive community. 2. A barrier develops, dividing the species. 3. Separated into different habitats, the divided populations become differentiated through the accumulation of differences. 4. So different have the separate populations become, that is when the barrier disappears and they overlap again. Interbreeding does not occur. Speciation Allopatric Speciation The formation of species (speciation) requires reproductive isolation, which can occur as a by-product of evolutionary change. Reproductive isolation can occur by at least nine different mechanisms, some occurring before mating, and some after mating. Geographic isolation is NOT always necessar...
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