Endemism and Isolation in Mountain Ecosystems

High mountains function ecologically as "sky islands": patches of cool, high-elevation habitat separated from one another by a surrounding "sea" of unsuitable lowland terrain, much as true islands are separated by ocean. This isolation restricts gene flow between populations on different peaks or ranges, favoring allopatric speciation and producing concentrations of species found nowhere else. The term gained wide currency through work on the Madrean Sky Island Archipelago, the forested mountain ranges scattered across southeastern Arizona, southwestern New Mexico, and northern Sonora, described in detail by the ecologist Peter Warshall in the mid-1990s.