In the Chiricahua Mountains in Arizona, a species of spider is found in both the woodland areas around streams and in the desert shrub areas. In the woodland areas, these spiders are under constant threat of predation from birds. Because of this, they spend little time in the exposed portion of their sheet webs. However, in the desert areas where birds are less of a threat, spiders constantly forage in the exposed portion of their webs. Offspring of matings between spiders from woodland and desert regions behave more like spiders from the desert habitat, even if they are living in the woodland area. The offspring quickly fall prey to birds, often before they have had a chance to reproduce. Over time, two different species arise. What type of reproductive barrier led to this speciation event?

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The speciation event described is a result of geographical barriers. The different environments (woodland and desert) in the Chiricahua Mountains led to different behaviors and adaptations in the spider populations, eventually causing them to evolve into separate species due to the distinct selective pressures in each habitat.

In the Chiricahua Mountains in Arizona, a Species of Spider