Because the finch in the North American forrest would be subjected to tree harvesting and forrest fires, unlike the island finch, which would be more hidden
Speciation is the formation of new and distince species over time. High rates of genetic variation can reduce the differences between different groups, which makes them more similar. Since there is less genetic variation between groups, there is less speciation. Genetic variation is expected to be less when animals have less mobility, like on a small island. Basically, this means that when changes happen, they happen less frequently, but therefore alter some members of the species and not others. This creates more speciation.
