Temperature is an important factor that defines species distributions. Reaching a general understanding of where temperature directly limits species’ ranges could help explain the distribution of life and improve predictions of the sensitivity of species to climate change. We test hypotheses about how the role of temperature in limiting ectotherm ranges differs across latitude and realms by comparing the temperatures and areas species occupy to those they could potentially occupy based on their physiological thermal tolerances.
Results/Conclusions
While lower-latitude species occupy ranges more closely related to their temperature tolerances, high-latitude terrestrial ectotherms generally under-occupy temperatures at their warm tolerance limits and are absent from thermally-tolerable areas towards the equator. This supports the hypothesis that range expansion into higher latitudes resulted in biotic exclusion within the tropics. Terrestrial species appear to over-occupy their potential ranges according to their cold tolerance limits, especially at higher latitudes, a finding partly explained by acclimatization and seasonal dormancy. In contrast to terrestrial patterns, marine species occupy temperatures that more closely match their thermal tolerance limits. Our findings support the Out-of-the-Tropics Trade-Off Hypothesis on land and suggest that range edges of marine species, broad–ranging species, and cool range edges of terrestrial ectotherms will be most directly responsive to climate warming.
