Biogeography on the eve of the twenty-first century: Towards an epistemology of biogeography

To reconstruct the spatio-temporal development of life on earth biogeographers have traditionally used several units of analysis and various kinds of data. The species has long been a fundamental unit, and a map of a species' distribution a basic datum. Some recent workers reject the biological species concept and advocate a phylogenetic one instead. Just as the definition of species may be changing, new technology and new mapping techniques are enlarging the concept of map. Through area cladograms, cladistics has modified the way taxonomic and area relationships are considered. Biogeography at the end of the 20th century thus is a conglomerate of old and new concepts, and of classic and revised interpretations. However, a literature review shows that, whether they use older trends or newer approaches, and irrespective of the school of thought they adhere to, biogeographers try to answer three hierarchically interrelated questions: (1) What are the patterns of geographical distribution? (2) What processes explain these patterns? and (3) How are these processes controlled? Pattern recognition is indispensable for any further work, process identification is concerned with proximate explanation, and process control seeks ultimate causation and may lead to theoretical considerations.