The Mediterranean basin, California, Chile, the western Cape of South Africa, and southern Australia share a Mediterranean climate characterized by cool, wet winters and hot, dry summers. These five regions have differing patterns of human settlement, but similarities in natural vegetation and some faunal assemblages. These likenesses are enhanced with time by an increasing level of biotic exchange among the regions. An initiative of a subcommittee of SCOPE (Scientific Committee on Problems of the Environment), which realized that the integrity of many natural ecosystems is being threatened...