The tropics, and their moist forests in particular, harbour more species than anywhere else on the planet. But what generates this diversity?
Traditional approaches to answering this question have focused on ecological factors such as rainfall and temperature, or historical factors such as recent glaciation, say Stuart Pimm and James Brown in this article. A third, more recent, approach explains the phenomenon as statistical consequence of varying geographical ranges between species — some are large, some are small and the tropics is where they overlap.
Patterns of biodiversity are likely to have multiple causes, they say. As well as being an intellectual conundrum, predicting these patterns is an urgent practical problem because extinctions are concentrated in areas of highest biodiversity.
Reference: Science 304,831 (2004)