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

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)(2007)(2008) to earlier surveys (1927)(1928)(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.

Environmental change and declining resource availability for small‐mammal communities in the Great Basin

“…The regional ecosystem is cold temperate semidesert, with local habitats along the elevational gradient ranging from desert shrublands to alpine tundra. Conditions here have, on average, become warmer (summer maximum temperature þ0.948 6 0.098C, mean 6 SE) and wetter (winter precipitation þ17.68 6 0.87 mm) over the past 80 years (Rowe et al 2010). Habitat alteration has been most profound at low elevations, where changes in climate and land use (e.g., fire suppression and grazing by domestic livestock) have facilitated the expansion of piñon-juniper woodland into sagebrush steppe and the encroachment of shrubland into areas previously dominated by grasses and open habitat (Miller and Rose 1999, Weisberg et al 2007, Bradley and Fleishman 2008, Rowe et al 2010.…”

“…Modern sampling protocols directly followed historical precedence, and both surveys spanned the latitudinal and elevational extent of the mountain range (Rowe et al 2010). For the analysis of aggregate community properties we limited our data to sites surveyed over multiple consecutive nights during the summer months (May-August), for a total of 12 historical and 21 modern sites, nine of which represent paired resurveys at precise locations.…”

Spatially heterogeneous impact of climate change on small mammals of montane California

“…However, we detected few contractions at lower limits of low-elevation mammals (figure 3), and shifts were significantly more common at their upper limits where potential land-use impacts were less evident. Greater heterogeneity in responses of lowelevation species may reflect stronger biotic influences [25,31], such as interspecific competition [40], seral dynamics of habitats [31] and the spread of invasive species [32]. Indeed, for the Central region, low-elevation species tracked changes in the extent of preferred habitats more closely than high-elevation taxa [46].…”

“…Heterogeneity in movements of species has been partly explained by incorporating local-scale measures of climatic change for both temperature and precipitation [14,30]; increases in the former usually favour upslope shifts, while increases in the latter typically favour downslope movements. Local changes in habitat structure owing to fire and grazing are also factors in some areas [31,32].…”

Biology in the Anthropocene: Challenges and insights from young fossil records

“…Ecologists and conservation biologists increasingly recognize that unexpected relationships and outcomes often emerge as study durations exceed a decade, that directional change in climate and other environmental factors can compromise experimental controls, and that most field experiments incorporate legacy effects, such as species depletion or habitat change, that are only later appreciated (e.g., refs. [32][33][34].…”