Oceanic islands have unbalanced biotas— they are missing major groups of organisms, and the same ones are missing on different islands. But the types of organisms that are there often comprise many similar species—a radiation—and they are the types of species, like birds and insects, that can disperse most easily over large stretches of ocean. And the species most similar to those inhabiting oceanic islands are usually found on the nearest mainland, even though their habitats are different.
