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USGS - science for a changing world

Russell Davis

The present distribution of the Mexican vole (Microtus mexicanus) is not entirely the product of post-Pleistocene forest fragmentation and extinction; recent dispersal also is indicated. Literature records further suggest that this phenomenon may reflect a general pattern of northward range expansion in many southwestern mammal species. Published in Western North American Naturalist, volume 52, issue 3, in 1992.
Distribution changes over the past one hundred years are summarized for a number of terrestrial mammals and birds in Arizona and New Mexico. At least 39 species appear to have been extirpated or suffered range restrictions, while 55 others have experienced range expansions. Even when exotics are excluded, the biodiversity of endotherms is now greater than in 1890. As expected, the ranks of the "losers" contain a disproportionate number of large predators and grassland-associated animals. By way of contrast, the majority of the "winners" were forest and/or scrubland-adapted species. More germane to this study was the fact that more than 70 percent of the "winners" were species that have their primary biotic affinity...
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