The scaling of heat tolerance with size in ectotherms

A body of evidence indicates that animals are decreasing in size as a general response to global warming. This reduction in size is actually proposed as a third universal response to global warming, together with the displacement in species ranges and phenological shifts. However, the mechanisms that explain such a pattern remain poorly understood.

Ignacio Peralta-Maraver (@DrIgnacioPM2), who has recently joined the Modeling Nature with a contract Juan de la Cierva, and his colleague Enrico L. Rezende from the Pontificia Universidad Católica de Chile, show that heat tolerance scales predictably with body size in ectothermic animals. They have recently published their findings in Nature Climate Change, which is considered the most influential journal in Environmental Science.

Authors employ the thermal death time curves, which take into consideration both the intensity and the duration of a thermal stress, to develop their analytical framework. Within this approach, they demonstrate that smaller animals exhibit a higher tolerance to an acute heat stress than larger ones, but a lower tolerance to chronic exposition because their tolerance declines faster with time. This scaling signal is detected across mollusk, arthropod, fish, amphibian, and reptile speciesspanning nearly 9 orders of magnitude in size. Combining their models with well-stablished calculations of the metabolic rate, authors also demonstrate that larger organisms collapse at relatively lower metabolic levels than smaller ones with the increase of temperature. Finally, results evidence that variable exposure times to a thermal challenge remain a major confounding effect in previous large-scale studies, potentially overshadowing not only allometric effects on heat tolerance and thermal safety limits, but also adaptive variation along geographic gradients. Together, analyses indicate that heat waves and extreme temperatures have a differential impact on organisms depending on their body size, providing one strong explanation for the general reduction in size observed in different lineages as temperatures rise with anthropogenically-driven global warming.

Fig.1 This study shows that heat tolerance scales with body size in ectothermic animals (e.g. lizards) when considering both the magnitude and the intensity of the thermal challenge.

Ignacio Peralta-Maraver has recently joined Modeling Nature and the Department of Ecology (University of Granada) with a postdoctoral contract Juan de la Cierva.

Reference.

Peralta-Maraver, I., & Rezende, E. L. (2020). Heat tolerance in ectotherms scales predictably with body size.

Nature Climate Change, 1-6. https://doi.org/10.1038/s41558-020-00938-y