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Challenges 2018, 9(1), 4; https://doi.org/10.3390/challe9010004

Effects of Contingency versus Constraints on the Body-Mass Scaling of Metabolic Rate

Department of Biology, Juniata College, Huntingdon, PA 16652, USA
Received: 16 December 2017 / Revised: 16 January 2018 / Accepted: 17 January 2018 / Published: 29 January 2018
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Abstract

I illustrate the effects of both contingency and constraints on the body-mass scaling of metabolic rate by analyzing the significantly different influences of ambient temperature (Ta) on metabolic scaling in ectothermic versus endothermic animals. Interspecific comparisons show that increasing Ta results in decreasing metabolic scaling slopes in ectotherms, but increasing slopes in endotherms, a pattern uniquely predicted by the metabolic-level boundaries hypothesis, as amended to include effects of the scaling of thermal conductance in endotherms outside their thermoneutral zone. No other published theoretical model explicitly predicts this striking variation in metabolic scaling, which I explain in terms of contingent effects of Ta and thermoregulatory strategy in the context of physical and geometric constraints related to the scaling of surface area, volume, and heat flow across surfaces. My analysis shows that theoretical models focused on an ideal 3/4-power law, as explained by a single universally applicable mechanism, are clearly inadequate for explaining the diversity and environmental sensitivity of metabolic scaling. An important challenge is to develop a theory of metabolic scaling that recognizes the contingent effects of multiple mechanisms that are modulated by several extrinsic and intrinsic factors within specified constraints. View Full-Text
Keywords: allometry; body size; contextual multimodal theory; ectothermic vs. endothermic animals; metabolism; metabolic-level boundaries hypothesis; scaling; thermal conductance; thermoregulation allometry; body size; contextual multimodal theory; ectothermic vs. endothermic animals; metabolism; metabolic-level boundaries hypothesis; scaling; thermal conductance; thermoregulation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Glazier, D.S. Effects of Contingency versus Constraints on the Body-Mass Scaling of Metabolic Rate. Challenges 2018, 9, 4.

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