Patterns of species diversity: fact or artifact?

Abstract

The pattern observed in nature has often served as a compelling motivation for seeking the underlying processes which are assumed to control the pattern. Spatial and temporal patterns of species diversity are the most commonly observed and described from the study of recent and paleocommunities. These patterns include those found within a local or discrete region such as succession and changes along an environmental gradient and interregional or global patterns such as latitudinal diversity gradients and comparisons of the deep-sea and the continental shelf faunas. Many hypotheses have been advanced to explain these patterns in terms of differences in the biology of species adapted to different or changing environments. However, a more simple explanation is possible: that these patterns do not result from any specific biologic processes.We examine this possibility and show that succession can result from probabilistic immigration and local extinction of species, diversity gradients can result from probabilistic disturbance in naturally patchy environments, and that latitudinal gradients can be simply a function of the shape of the earth. As long as such diversity patterns can be explained independent of any specific biologic processes, they offer no test of the importance of these processes, either ecologically or evolutionarily.