Biomass of a trophic level increases with maximum body size, but less than proportionally

Abstract

A recent paper by Enquist and colleagues¹ took a very important step in predicting the ecosystemic effects of species losses on a global scale. Using Metabolic Scaling Theory (MST), they concluded that large-sized species contribute disproportionately to several ecosystem functions. One of their key predictions is that total biomass of animals in a trophic level (M_Tot, using their notation) should increase more than proportionally with its maximum body size (m_max), following the relationship M_Tot ∝ m_max^5/4. Here I argue that this superlinear scaling results from an incorrect representation of the individual size distribution and that the exponent should be 1/4, implying a sublinear scaling. The same reasoning applies to total energy flux or metabolism B_Tot, which should be invariant to maximum size according to the energetic equivalence and perfect compensatory responses entailed by MST.