The splitting up of an original biota into several isolated biotas (vicariants) by past geological or climatic events. The vicariants then develop independently and different species evolve. The process is presented as an alternative to the traditional theories of speciation by dispersal that have previously been used to explain biogeographical patterns. The existence of areas that contain many species different from but related to species in another distant area is taken by many as evidence for vicariance. One major event that is postulated as a means by which vicariants could have arisen is the fragmentation of the ancient land masses into the present-day continents (see continental drift
). This could explain the disjunct distributions of many genera, e.g. Liriodendron (tulip trees) and southern beeches (Nothofagus).