Which is an example of sympatric speciation?

Sympatric speciation occurs when new species arise from a single ancestral species while inhabiting the same geographic region. This process often involves the development of reproductive barriers that prevent populations from interbreeding, despite being in proximity to one another.

In the context of the given question, the first choice—two species developing different mating timeframes in the same region—is a classic example of sympatric speciation. When individuals of a species begin to breed at different times, they limit their opportunities to interbreed, leading to reproductive isolation. Over time, this isolation can result in divergent evolutionary paths, eventually resulting in the formation of two distinct species, even without any physical barriers separating them.

This contrasts with the other choices. The second choice refers to allopatric speciation, where populations become isolated geographically, allowing them to evolve independently. The third choice discusses a single species splitting due to a volcanic eruption, which implies a physical separation of populations, also indicative of allopatric speciation. Lastly, animal migration causing genetic mixing indicates gene flow between populations, which typically works against speciation. Overall, the correct answer focuses on the lack of geographic separation while still allowing for reproductive differentiation.