Expanding, shifting and shrinking: The impact of global warming on species’ elevational distributions

Abstract

Aim: Species are responding to climate warming by shifting their distributions toward historically cooler regions, but the degree to which expansions at cool range limits are balanced by contractions at warm limits is unknown. We synthesized published data documenting shifts at species’ warm versus cool range limits along elevational gradients to (a) test classic ecological theory that predicts temperature more directly influences species’ cool range limits than their warm range limits, and (b) determine how warming-associated shifts have changed the extent and area of species’ elevational distributions. Location: Global. Time period: 1802–2012. Major taxa studied: Vascular plants, endotherms, ectotherms. Methods: We compiled a dataset of 975 species from 32 elevational gradients for which range shifts have been measured at both warm and cool range limits. We compared the magnitude and variance of shifts at species’ warm versus cool limits, and quantified how range shifts have impacted species’ elevational extents and areas. Results: On average species have shifted upslope associated with temperature increases at both warm and cool limits (warm limit: 92 ± 455 m/C; cool limit: 131 ± 465 m/C; overall mean ± SD). There was no systematic difference in the magnitude or variance of shifts at warm versus cool limits and thus no indication that cool limits are more directly controlled by temperature. Species’ elevational extents and available area significantly decreased for mountaintop species. Main conclusions: Our results do not support the long-standing hypothesis that cool limits are more sensitive or responsive to temperature. We find that, across the globe, mountaintop species’ ranges are significantly shrinking as they shift upslope, supporting predictions that high elevation species are especially vulnerable to temperature increases. Our synthesis highlights the extreme variation in species’ distributional responses to warming, which may indicate that biotic interactions play a more prominent role in setting range limits than previously thought.