An oversimplification of physiological principles leads to flawed macroecological analyses

Abstract

Macrophysiological analyses are useful to predict current and future range limits and improve our understanding of endotherm macroecology, but such analyses too often rely on oversimplifications of endothermic thermoregulatory and energetic physiology, which lessens their applicability. We detail some of the major issues with macrophysiological analyses based on the classic Scholander-Irving model of endotherm energetics in the hope that it will encourage other research teams to more appropriately integrate physiology into macroecological analyses.

Figure 1

Demonstration of the inherent limitations of using body temperature (T _b) and the lower critical temperature (T _lc) of the thermal neutral zone to calculate thermal conductance (C) when T _b and T _lc are poorly defined. Buckley et al. (2018) analyzed metabolic expansibility, which is the metabolic rate at the range boundary (MR_RB) divided by basal metabolic rate (BMR). MR_RB, and therefore ME, changes drastically depending on assumptions of T _b and T _lc used to calculate C. Data are for a rock mouse (Chaetodipus intermedius, left; Bradley et al., 1975) and a hedgehog (Atelerix albiventris, right; McNab, 1980). In each case, black lines represent the T _b value used by Buckley et al and the various other lines represent plausible assumptions about T _b, assuming T _lc is constant. Dashed lines represent the extrapolation of T _b from the MR line assuming the animal is perfectly following Newton's Laws of Cooling. The inset in (a) is an expanded view encapsulating the T _lc and T _b of the rock mouse