Background/Question/Methods Understanding which ecological factors constrain species distributions is a fundamental goal in ecology and increasingly important to predicting climate change impacts. Darwin hypothesized that abiotic factors, especially climate, generally impose species’ high-latitude/elevation (‘cool’) range limits, whereas biotic interactions, especially competition, more often impose species’ low-latitude/elevation (‘warm’) limits. I present results from global data syntheses on 1) the frequency with which biotic and abiotic factors contribute to cool and warm range limits, and 2) the relative responses of cool and warm limits to climate warming.
Results/Conclusions > Biotic interactions influenced >60% of species range limits
> Biotic interactions influence warm limits more often cool limits
> Temperature contributes strongly to both cool and warm limits
> Both cool and warm limits are responding to warming, but with substantial variation among range limits
> Cool limits have not responded more strongly or consistently to warming
Our results suggest that biotic interactions and temperature to contribute to most range limits, and that predicting responses at the species level will be extremely challenging.