The diversity within the wild bird species in the diagram below can best be explained by which process?

Adaptative radiation caused a group of finches on Galapagos Island to have different beak sizes. Adaptive radiation is the process of distinct species in a certain geographical area evolving from a single point and literally radiating to other parts of geography (habitats). They are especially common in closely related groups that have evolved over a short period of time. These finches were naturally selected and constituted the basis of their species' diversity.