Tamanho, formato e nicho termal de endotermos

Size, shape, and the thermal niche of endotherms
Warren P. Portera,1 and Michael Kearneyb
+ Author Affiliations

aDepartment of Zoology, University of Wisconsin, Madison, WI 53706; and

bDepartment of Zoology, University of Melbourne, Victoria 3010, Australia

Edited by Elizabeth A. Hadly, Stanford University, Stanford, CA, and accepted by the Editorial Board September 20, 2009 (received for review July 5, 2009)

Abstract

A key challenge in ecology is to define species' niches on the basis of functional traits. Size and shape are important determinants of a species' niche but their causal role is often difficult to interpret. For endotherms, size and shape define the thermal niche through their interaction with core temperature, insulation, and environmental conditions, determining the thermoneutral zone (TNZ) where energy and water costs are minimized. Laboratory measures of metabolic rate used to describe TNZs cannot be generalized to infer the capacity for terrestrial animals to find their TNZ in complex natural environments. Here, we derive an analytical model of the thermal niche of an ellipsoid furred endotherm that accurately predicts field and laboratory data. We use the model to illustrate the relative importance of size and shape on the location of the TNZ under different environmental conditions. The interaction between body shape and posture strongly influences the location of the TNZ and the expected scaling of metabolic rate with size at constant temperature. We demonstrate that the latter relationship has a slope of approximately ½ rather than the commonly expected surface area/volume scaling of ⅔. We show how such functional traits models can be integrated with spatial environmental datasets to calculate null expectations for body size clines from a thermal perspective, aiding mechanistic interpretation of empirical clines such as Bergmann's Rule. The combination of spatially explicit data with biophysical models of heat exchange provides a powerful means for studying the thermal niches of endotherms across climatic gradients.

biophysical ecology functional traits lower critical temperature metabolic scaling thermoneutral zone

Footnotes

1To whom correspondence should be addressed. E-mail: wpporter@wisc.edu

Author contributions: W.P.P. and M.K. designed research; W.P.P. and M.K. performed research; W.P.P. contributed new reagents/analytic tools; W.P.P. and M.K. analyzed data; and M.K. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission. E.A.H. is a guest editor invited by the Editorial Board.

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