WAKE, D; Univ. of California, Berkeley: Effects of altitudinal gradients on salamander biodiversity in tropical America

Salamanders are abundant in Middle America and in Colombia but almost nowhere else in the tropics. The areas of greatest abundance are characterized by extreme topographic diversity and by unstable and shifting geology. Elevational transects from Veracruz, Mexico, to western Panama, on both sides of the continental divide, characteristically have the greatest diversity in mid-elevational cloud forests, and at high elevation, with most species showing sharp elevational limits. There is evidence both of allopatric species formation in closely adjacent regions separted by areas of lower elevation, and parapatric species formation along single gradients. In some instances zones of parapatry are very finely divided, suggesting narrow adaptation to discrete microhabitats, such as bromeliads, even on very local scales. These examples are used to make an argument that species formation in these amphibians and buildup of biodiversity is a direct consequence of physical aspects of the environment.