Metabolic Scaling in Animals: Methods, Empirical Results, and Theoretical Explanations

Abstract

Life on earth spans a size range of around 21 orders of magnitude across species and can span a range of more than 6 orders of magnitude within species of animal. The effect of size on physiology is, therefore, enormous and is typically expressed by how physiological phenomena scale with mass(b). When b ≠ 1 a trait does not vary in direct proportion to mass and is said to scale allometrically. The study of allometric scaling goes back to at least the time of Galileo Galilei, and published scaling relationships are now available for hundreds of traits. Here, the methods of scaling analysis are reviewed, using examples for a range of traits with an emphasis on those related to metabolism in animals. Where necessary, new relationships have been generated from published data using modern phylogenetically informed techniques. During recent decades one of the most controversial scaling relationships has been that between metabolic rate and body mass and a number of explanations have been proposed for the scaling of this trait. Examples of these mechanistic explanations for metabolic scaling are reviewed, and suggestions made for comparing between them. Finally, the conceptual links between metabolic scaling and ecological patterns are examined, emphasizing the distinction between (1) the hypothesis that size- and temperature-dependent variation among species and individuals in metabolic rate influences ecological processes at levels of organization from individuals to the biosphere and (2) mechanistic explanations for metabolic rate that may explain the size- and temperature-dependence of this trait.

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

“…As further evidence, when the effects of activity are removed in an actively mobile species, such as the fish Coregonus albula, T a and the resting metabolic scaling exponent are strongly negatively correlated [115], as predicted by the MLBH [16,26]. Further studies of the effects of various abiotic and biotic ecological factors on metabolic scaling would also be worthwhile (see also [10,16,22,26,32,41,[44][45][46]48]). …”

“…My interpretation of these contingent thermal effects contributes to a growing revival of the old, controversial view that thermoregulation is importantly involved in the metabolic scaling of endotherms ( [10][11][12]16,[23][24][25][26][27][28]32,56,58,87,89,93], but see [9,21,22,33,92,116,117]). This thermoregulatory view is testable.…”

Why does offspring size affect performance? Integrating metabolic scaling with life-history theory

“…Oxygen consumption was measured using a 24-channel PreSens sensor dish reader (Sensor Dish Reader SDR2, PreSens), with 24-chamber glass micro plate (200 ml) (Loligo Systems Aps, Tjele, Denmark) according to standard techniques [47,48]. Individual larvae or settlers were placed in a glass vial containing 0.2 mm filtered seawater and a non-consumptive O 2 sensor spot and _ V O2 was calculated from the rate of change of O 2 saturation (m a ; %h 21 [26]), where m b is the rate of change of O 2 saturation for blank vials containing no larvae or in the case of settlers, only acetate (%h 21 ), b O2 is the oxygen capacitance of air-saturated (AS) seawater at 17.58C (5.8 ml l 21 ; [49]) and V is water volume (chambers were 2.0 Â 10 24 l, and water volume was calculated by subtracting the volume of acetate and animals). Four blank vials were recorded simultaneously to account for microbial oxygen consumption, and sensor spots were calibrated with AS seawater (100% AS) and water containing 2% sodium sulfite (0% AS).…”

Rediscovering and Reviving Old Observations and Explanations of Metabolic Scaling in Living Systems

“…Many investigators (but surprisingly not Kleiber himself, a founder of the 3/4-power law) rejected the thermoregulatory surface-area model of metabolic scaling, because it seemed incapable of explaining 3/4-power scaling, especially in ectothermic organisms that do not actively maintain constant body temperatures (see also [20]). Furthermore, the metabolic scaling slope does not necessarily approximate the theoretical values of 2/3 or 3/4, but may vary extensively between ~0 and >1, in association with differences in taxonomic affiliation, lifestyle, developmental stage, physiological status, and various ecological factors (e.g., [19,20,23,24,26,27,32,34,39,[44][45][46][47][48][49][54][55][56][57][58][59][60][61][72][73][74][75][76][99][100][101][102][103][104][105][106][107][117][118][119][120][121]). …”

“…First, changes in temperature can affect not only the elevation, but also the slope of metabolic scaling relationships, both within and among species (see Section 2.1.4), as predicted by the MLBH [19,46,54,56,57,59,129] and the viscosity hypothesis of Verberk and Atkinson [256]. Second, several other kinds of abiotic and biotic factors may influence metabolic scaling slopes (reviewed in [19,20,56,103,121]). Third, evidence is growing that RTN-constrained supply of oxygen and nutrients does not universally, or even typically control metabolic rate and its scaling with body size (see Sections 2.2.2 and 3.3).…”