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Range dynamics of small mammals along an elevational gradient over an 80-year interval

Authors

  • REBECCA J. ROWE,

    1. Utah Museum of Natural History, University of Utah, 1390 East Presidents Circle, Salt Lake City, UT 84112, USA
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  • JOHN A. FINARELLI,

    1. Department of Geological Sciences, University of Michigan, 2534 C. C. Little Building, 1100 North University Avenue, Ann Arbor, MI 48109, USA
    2. University of Michigan Museum of Paleontology, 1529 Ruthven Museum, 1109 Geddes Road, Ann Arbor, MI 48109, USA
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  • ERIC A. RICKART

    1. Utah Museum of Natural History, University of Utah, 1390 East Presidents Circle, Salt Lake City, UT 84112, USA
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Rebecca J. Rowe, tel. +801 585 7759, fax +801 585 3684, e-mail: rrowe@umnh.utah.edu

Abstract

One expected response to observed global warming is an upslope shift of species elevational ranges. Here, we document changes in the elevational distributions of the small mammals within the Ruby Mountains in northeastern Nevada over an 80-year interval. We quantified range shifts by comparing distributional records from recent comprehensive field surveys (2006–2008) to earlier surveys (1927–1929) conducted at identical and nearby locations. Collector field notes from the historical surveys provided detailed trapping records and locality information, and museum specimens enabled confirmation of species' identifications. To ensure that observed shifts in range did not result from sampling bias, we employed a binomial likelihood model (introduced here) using likelihood ratios to calculate confidence intervals around observed range limits. Climate data indicate increases in both precipitation and summer maximum temperature between sampling periods. Increases in winter minimum temperatures were only evident at mid to high elevations. Consistent with predictions of change associated with climate warming, we document upslope range shifts for only two mesic-adapted species. In contrast, no xeric-adapted species expanded their ranges upslope. Rather, they showed either static distributions over time or downslope contraction or expansion. We attribute these unexpected findings to widespread land-use driven habitat change at lower elevations. Failure to account for land-use induced changes in both baseline assessments and in predicting shifts in species distributions may provide misleading objectives for conservation policies and management practices.

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