ABSTRACT
The geographical limits of the area within which a particular population of organisms occurs are known as its range. The aim of historical biogeography then is to reconstruct the origin, spread, and extinction of taxonomic groups of organisms through time and to explain the influence of past geological and climatic events on distributions. French plant geographers have long distinguished a hierarchy of floral regions: regions, with a high proportion of endemic genera; domains, with a high proportion of endemic species; and sectors and subsectors with a high proportion of subspecies or ecotypes. The range of variation within a species population should theoretically be less than that between it and any other species population. Speciation is the evolutionary process whereby new species come into being. The geographical area in which a species originated and from which it has spread is difficult to establish. Species migration or range extension will obviously involve only part of the potential parent gene pool.
