Vicariance Biogeography

Biogeography is a discipline that aims to integrate multiple fields of inquiry to understand the spatial distribution of organisms. It draws from the fields of ecology, evolution, geography, geology, and Earth history to provide an explanation about what lives where and why. A specific subdiscipline of biogeography is vicariance biogeography, which focuses on the process of vicariance—the physical separation of a population, typically by a geographic barrier—as the source of new species. Vicariance biogeography thus attempts to explain the distribution of organisms that have achieved their place through a process of cladogenesis due to the emergence of a barrier, such as a newly formed body of water, a new mountain range, a newly established water current, etc. Such structures will prevent gene flow most readily in organisms that display low vagility or a narrow ecological tolerance. A paradigmatical example of vicariance biogeography is the signature that the breakup of Gondwana left on its biota, as such organisms achieved their modern distribution while riding on tectonic plates, which now allows us to trace the geological history of the continents’ movements. Traditionally approached by generating area cladograms—evolutionary trees that substituted taxa for geographic areas—today requires a temporal framework to justify the process of vicariance and distinguish it from dispersal. Vicariance is still found as the preferred biogeographical explanation for many groups of non-volant organisms that do not have a dispersal phase (e.g., certain kinds of larvae, seeds, or resistant bodies). However, many traditional examples of vicariance biogeography (e.g., the distribution of modern ratites or the Southern beech) are now rejected by evolutionary studies that have included a timed phylogeny. It is also well accepted that dispersal continues to play an important role in the distributions of many other organisms.