A History of Transition Zones in Biogeographical Classification

Transition zones are problematic in biogeographical classification as they represent artificial areas. A review of transition zones into existing biogeographical classifications shows conflicting area taxonomies. While many authors consider transition zones as overlap zones or areas of biotic mixing, only a few have considered excluding them from biogeographical classification altogether. One way of incorporating transition zones into a natural classification is by treating them as artefacts of geographically overlapping temporally disjunct areas. In doing so, geographically overlapping areas may occupy the same space but have different boundaries and histories. Temporally disjunct areas do form natural hierarchical classifications, as seen in the paleobiogeographical literature. A revision of each transition zone will determine whether they are artificial areas, areas within their own right or potentially geographically overlapping temporally disjunct regions.