Physiological Limits along an Elevational Gradient in a Radiation of Montane Ground Beetles.

Rachel A Slatyer,Sean D Schoville,Joshua B Benoit

doi:10.1371/journal.pone.0151959

Rachel A Slatyer, Sean D Schoville + Show 1 more

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https://doi.org/10.1371/journal.pone.0151959

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Abstract

A central challenge in ecology and biogeography is to determine the extent to which physiological constraints govern the geographic ranges of species along environmental gradients. This study tests the hypothesis that temperature and desiccation tolerance are associated with the elevational ranges of 12 ground beetle species (genus Nebria) occurring on Mt. Rainier, Washington, U.S.A. Species from higher elevations did not have greater cold tolerance limits than lower-elevation species (all species ranged from -3.5 to -4.1°C), despite a steep decline in minimum temperature with elevation. Although heat tolerance limits varied among species (from 32.0 to 37.0°C), this variation was not generally associated with the relative elevational range of a species. Temperature gradients and acute thermal tolerance do not support the hypothesis that physiological constraints drive species turnover with elevation. Measurements of intraspecific variation in thermal tolerance limits were not significant for individuals taken at different elevations on Mt. Rainier, or from other mountains in Washington and Oregon. Desiccation resistance was also not associated with a species’ elevational distribution. Our combined results contrast with previously-detected latitudinal gradients in acute physiological limits among insects and suggest that other processes such as chronic thermal stress or biotic interactions might be more important in constraining elevational distributions in this system.

Highlights

Studies of environmental gradients are critical to developing a mechanistic understanding of how biotic and abiotic factors regulate species diversity and distributions [1]
We tested the hypothesis that physiological limits, measured as temperature and desiccation tolerance, were associated with the elevational ranges of the Nebria species on Mt
Despite a steep decline in minimum microclimate temperatures with elevation, we found no evidence of variation in acute cold tolerance or desiccation resistance among species

Summary

Introduction

Studies of environmental gradients are critical to developing a mechanistic understanding of how biotic and abiotic factors regulate species diversity and distributions [1]. In the absence of physical barriers, range limits are expected to reflect the limits of the fundamental niche, describing the resources required for a species to persist in a given environment [6, 7] Factors such as dispersal ability and biotic interactions can constrain species to a subset of their potential range (i.e. the realised niche [6,7,8,9]), physiological limits–as a component of the fundamental niche–are considered to be relevant in mountain environments and are frequently inferred as proximate drivers of elevational range limits [10,11,12,13]. If physiological constraints determine a species’ elevational range, tolerance limits should be statistically associated with climatic characteristics at the range edge; species occupying different elevational ranges would exhibit differences in tolerance limits [13, 18,19,20]

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