The aerobic scope is clearly linked to the supply–demand spectrum as quantified by DEB theory

Abstract

Supply-species typically eat what is available, while demand-species eat what they need, almost independently of what is available. The trait ‘supply stress’ quantifies the supply–demand spectrum, in the context of the Dynamic Energy Budget (DEB) theory. This dimensionless trait is defined as the maturity maintenance times the squared somatic maintenance, divided by the cubed assimilation. This function of DEB parameters is mostly estimated from data on growth, reproduction and life history, typically applied for fully grown individuals. Only a minority of the over 7300 species in the Add-my-Pet collection also have respiration data, combined with other data. Consistent with a set of traits that characterizes the supply/demand spectrum, birds and mammals score high on the supply stress, reptiles, amphibians, cartilaginous fish score moderate and ray-finned fish and invertebrates score low. The structure of the standard DEB model explains why species must have a low supply stress to allocate a large fraction of their assimilation to reproduction. We show this for large taxa, but also for rodents, compared to carnivorans, where rodents have a lower position in the food chain. We list and discuss ecophysiological properties that characterize the spectrum. A decade ago, the factorial aerobic scope (FAS), i.e. the ratio of the maximum and basal metabolic rate (MMR and BMR), was predicted to be high for species at the demand-end of the spectrum, and low for those at the supply-end. The aim of this paper is to test this prediction for respiration data from the literature. Our conclusion is that the FAS indeed increases for increasing supply stress, but the scatter is substantial. The FAS roughly increases from 3.2 at zero supply stress to 32 at maximum supply stress. We discuss an application of this finding for the estimation of the maturity maintenance rate coefficient from data, which is otherwise difficult with simple data. We also discuss the large scatter of respiration rates and show, with a computer simulation study of the standard DEB model, that a little scatter in food intake translates into a much larger scatter of respiration rates. Despite the scatter, the measured BMR was found to be close to the DEB-predicted field metabolic rate. This is remarkable because DEB theory makes no direct assumptions about respiration, but can still predict it exploiting the conservation laws for the chemical elements C, H, O and N. Our findings not only suggest functionalities of the aerobic scope in a wider context, but also support the concept of maturity maintenance, which is key to DEB theory, but hard to make concrete.