Biogeography and the Distribution of Cave Collembola

Abstract

The cave collembola of the U.S. and Mexico were studied to see whether they supported one or another view of the controversies surrounding three questions concerning biogeography: (1) whether signifi- cant novelty tends to occur centrally and move out, or start in peripheral isolates; (2) whether the present distribution of organisms is better explained by dispersionist or vicariance views or a mix of both; and (3) the applicability and value of the panbiogeographic method of analysis and its relationship to different theories of biogeography. We plotted the distribu- tion of monophyletic groups or lineages of those groups with considerable development in caves. We also determined the level of cave adaptation of each of seventy-eight cave species of the genera Sinella, Pseudosinella, Metasinella and Troglopedetes. These data were then used to address the questions listed above. There does not appear to be any clear tendency for central or peripheral location for the origin of evolutionary novelty. Second, the present distribution of cave collembola is clearly best explained by a combination of vicariance and dispersion events. Third, the panbiogeographic model is of limited use as an indicator of probable past dispersal events.