Scaling up the curvature of mammalian metabolism

Abstract

A curvilinear relationship between mammalian metabolic rate and body size on a log-log scale has been adopted in lieu of the longstanding concept of a 3/4 allometric relationship (Kolokotrones et al., 2010). The central tenet of Metabolic Ecology (ME) states that metabolism at the individual level scales-up to drive the ecology of populations, communities and ecosystems. If this tenet is correct, the curvature of metabolism should be perceived in other ecological traits. By analyzing the size scaling allometry of eight different mammalian traits including basal and field metabolic rate, offspring biomass production, ingestion rate, costs of locomotion, life span, population growth rate and population density we show that the curvature affects most ecological rates and times. The prevalence of this non-linearity can be put forward as a proof for the real existence of the curvature described in mammalian basal metabolic rate and as support for ME. However, the curvilinear relationship between metabolic rate and body size does not allow an analytical solution for the scaling equations of the Metabolic Theory of Ecology (MTE). Numerical simulations of the ontogenetic growth model used by MTE to scale from metabolism to developmental times show that the resulting body mass scaling for developmental time and traits at the population level would be curvilinear but with different scaling coefficients. This prevents the full acceptance or rejection of MTE on the basis of the coincidence or lack of coincidence of the exact values of the scaling exponents of different traits.