Many songbirds breed in North America in the spring and summer and then migrate to Central and South America in the fall. They spend the winter in these warmer areas, where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast. What can you say about the isolating mechanisms of these two species? They must have strong postzygotic isolating mechanisms to spend winter in such close proximity. Reinforcement must be occurring when they winter together. They must have strong prezygotic isolating mechanisms to spend winter in such close proximity. Their winter habitat has no bearing on their degree of reproductive isolation.
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This geographical isolation is a form of prezygotic isolating mechanism, as it prevents the two species from mating and producing hybrid offspring. Secondly, the fact that the two species overwinter together in mixed flocks in Costa Rica does not necessarily mean Show more…
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