Dispersal or vicariance?

Before continental drift was known about, the main process believed to alter biogeographic distributions was dispersal. Taxonomic groups were thought to originate in one confined area, called the center of origin, and then descendant populations dispersed away from it. How can we tell whether dispersal or vicariance is responsible for a particular biogeographic distribution? Vicariance biogeographers test their idea by two methods, one of which, area cladograms, will be introduced in this tutorial.

Does the pattern of splitting in one group match the geological history of the region where it lives? The first major piece of vicariance biogeographic research, by Brundin in 1966, is shown opposite. He studied the Antarctic chironomid midges. These midges are distributed around the southern hemisphere.

Figure: biogeography of chironomid midges in the southern hemisphere. The midges live in the regions indicated in black. From Brundin (1989).