SPLENDID ISOLATION - PATTERNS OF GEOGRAPHIC RANGE COLLAPSE IN ENDANGERED MAMMALS

Population densities of terrestrial animals tend to be higher and less variable near the center versus along the periphery of a species' geographic range. If extinctions are tied to local population dynamics, geographic ranges of endangered species should collapse inward, with remnant populations persisting near the center of a species' historic range. Geographic-Information-System analysis of range collapse in nonvolant, terrestrial mammals reveals, however, that extant populations of 23 of 31 species were located along the periphery, not the center, of their historic range. In addition, range collapse appears to be independent of fragment area and has a directional bias from east to west. Persistence of endangered populations also appears to be greater on islands than on continents. These results contradict conventional wisdom in biogeography and macroecology and have important implications for conserving biodiversity. Because of their relative isolation from central populations and from a suite of anthropogenic disturbances, islands and other sites along the periphery of a species' historic range represent critical refugia for many endangered species.