title: Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals.
abstract: The extent to which different kinds of organisms have adapted to environmental temperature regimes is central to understanding how they respond to climate change. The Scholander-Irving (S-I) model of heat transfer lays the foundation for explaining how endothermic birds and mammals maintain their high, relatively constant body temperatures in the face of wide variation in environmental temperature. The S-I model shows how body temperature is regulated by balancing the rates of heat production and heat loss. Both rates scale with body size, suggesting that larger animals should be better adapted to cold environments than smaller animals, and vice versa. However, the global distributions of ∼9,000 species of terrestrial birds and mammals show that the entire range of body sizes occurs in nearly all climatic regimes. Using physiological and environmental temperature data for 211 bird and 178 mammal species, we test for mass-independent adaptive changes in two key parameters of the S-I model: basal metabolic rate (BMR) and thermal conductance. We derive an axis of thermal adaptation that is independent of body size, extends the S-I model, and highlights interactions among physiological and morphological traits that allow endotherms to persist in a wide range of temperatures. Our macrophysiological and macroecological analyses support our predictions that shifts in BMR and thermal conductance confer important adaptations to environmental temperature in both birds and mammals.
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, NM 87131; Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; tfristoe@wustl.edu jhbrown@unm.edu.
authors.forename: Trevor S
authors.initials: TS
authors.lastname: Fristoe
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, NM 87131; Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Burger
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, NM 87131;
authors.forename: Meghan A
authors.initials: MA
authors.lastname: Balk
authors.affiliation: Senckenberg Biodiversity and Climate Research Centre, Senckenberg Gesellschaft für Naturforschung, 60325 Frankfurt, Germany; Zoology Department, Ghazi University, 32200 Punjab, Pakistan.
authors.forename: Imran
authors.initials: I
authors.lastname: Khaliq
authors.affiliation: Senckenberg Biodiversity and Climate Research Centre, Senckenberg Gesellschaft für Naturforschung, 60325 Frankfurt, Germany;
authors.forename: Christian
authors.initials: C
authors.lastname: Hof
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, NM 87131; tfristoe@wustl.edu jhbrown@unm.edu.
authors.forename: James H
authors.initials: JH
authors.lastname: Brown
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000465:Algorithms; D000818:Animals; D001481:Basal Metabolism / Q000502:physiology; D001717:Birds / Q000145:classification / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology*; D057231:Climate Change; D004734:Energy Metabolism / Q000502:physiology*; D004777:Environment; D008322:Mammals / Q000145:classification / Q000502:physiology*; D008954:Models, Biological; D013045:Species Specificity; D013696:Temperature; D022722:Thermogenesis / Q000502:physiology*; D013997:Time Factors
keywords: Bergmann’s rule; body size; macrophysiology; metabolic rate; thermal conductance