Montane Mammals of the American Southwest: The Possible Influence of Post-Pleistocene Colonization

Abstract

Insular biogeographical theory was used to analyse the current assemblages of forest-dwelling species of small, non-flying mam- mals on the mountains of New Mexico and adjacent parts of Arizona. These montane islands of forest habitat are surrounded by woodlands and grasslands, without major intervening desert scrub barriers to north-south colonization. The source of the species included in the analysis was assumed to be the southern extension of the Rocky Mountains in northern New Mexico. Three variables were included in this analysis: species rich- ness, area and isolation (as estimated by two measures of distance from the source). In multiple regression analysis, both area and isolation were found to have significant contributions to the variation in the numbers of species on these montane islands. Similar results were also obtained from an analysis of data from the literature for a larger region of the American Southwest. These results, which differ from those for montane species assemblages in the Great Basin, suggest that the present distributions of mammals on mountains in New Mexico and adjacent parts of Arizona have been influenced by the combined effects of post-Pleistocene colonization as well as vicariant events and subsequent extinctions.