Vicariance Events

Vicariance events are speciation events where a species' distribution becomes segmented and the separated populations evolve due to different selecting factors, causing the populations to become unique species. There are numerous ways that this can occur: by something as long and slow as the rising of a mountain range or the separation of Gondwana to something as quick as an erupting volcano. Many endemic species are due to vicariance and the separation of Gondwana. The island of Madagascar is an excellent example because of its location during the separation process; it was in the middle of two larger land masses that would eventually become the four southern continents (South America, Africa, Antarctica, and Australia) and another land mass that would become India. This make it easier to understand how Madagascar can have only one extant freshwater fish species who's closest relative is located on nearby Africa, but all the other freshwater species present have their closest relative on India and Australia.



Vicariance events do not have to be as dramatic as a super-continent dividing. It depends on whether the event makes it where gene flow can not occur; we have looked at examples where two populations have been separated but are still the same species because there is still gene flow between the populations like with the water snakes around Lake Erie. The gene flow between them kept one color morph of the snake from becoming its own unique species.

http://www.sciencedaily.com/releases/2012/08/120829151239.htm
http://evolution.berkeley.edu/evolibrary/news/091001_madagascar