EXTINCTIONS OF MONTANE MAMMALS RECONSIDERED - PUTTING A GLOBAL-WARMING SCENARIO ON ICE

McDonald and Brown developed a model based on island biogeographic pri nciples to predict the magnitude and composition of small mammal extin ctions from isolated boreal habitats atop mountains of the Great Basin following global warming. The model predicts that three of 14 boreal mammals will go extinct regionally and that four of 19 mountain ranges will lose upwards of 50% of their present faunas. Here, we re-examine the model on the basis of its underlying assumptions, on the statisti cal and biogeographic protocols used, and on its predictive power. A k ey assumption, that populations of these small mammals are isolated by absolute barriers to dispersal, is challenged by published field obse rvations and by extensive trapping records. Statistical procedures use d to construct the model are questionable and the model itself yields imprecise estimates. The biogeographic principle used to identify exti nction-prone species, nested subsets of species, makes predictions tha t are at odds with available autecological information. The demonstrat ion of a nested pattern of species occurrences does not provide defini tive evidence in resolving SLOSS - or whether a single large island or several small islands of equivalent total area will contain more spec ies. We conclude that the model is not a reliable method for forecasti ng species extinctions following global warming. The final resolution of the biogeography of montane mammals (and predictive models of extin ction) in the Great Basin must await a full and accurate accounting of past and present species distributions.