Global analysis of thermal tolerance and latitude in ectotherms

TLDR

Macroecology links physiological processes to large‑scale geographic patterns, and species at higher latitudes experience greater seasonal temperature variation, predicting greater tolerance to temperature extremes. The study examined how ectotherm thermal tolerance breadths relate to specimen latitude, controlling for habitat, hemisphere, methodology, and taxonomy. The analysis incorporated all available data, adjusting for habitat, hemisphere, methodological differences, and taxonomic affinity. Thermal tolerance breadths increase with latitude, especially in the Northern Hemisphere; terrestrial species show little change in upper limits but lower limits decline with latitude, whereas marine species exhibit poleward decreases in both limits, confirming and extending prior hypotheses and highlighting terrestrial–marine differences linked to temperature variability.

Abstract

A tenet of macroecology is that physiological processes of organisms are linked to large-scale geographical patterns in environmental conditions. Species at higher latitudes experience greater seasonal temperature variation and are consequently predicted to withstand greater temperature extremes. We tested for relationships between breadths of thermal tolerance in ectothermic animals and the latitude of specimen location using all available data, while accounting for habitat, hemisphere, methodological differences and taxonomic affinity. We found that thermal tolerance breadths generally increase with latitude, and do so at a greater rate in the Northern Hemisphere. In terrestrial ectotherms, upper thermal limits vary little while lower thermal limits decrease with latitude. By contrast, marine species display a coherent poleward decrease in both upper and lower thermal limits. Our findings provide comprehensive global support for hypotheses generated from studies at smaller taxonomic subsets and geographical scales. Our results further indicate differences between terrestrial and marine ectotherms in how thermal physiology varies with latitude that may relate to the degree of temperature variability experienced on land and in the ocean.