Phenotypic determinants of inter‐individual variability of litter consumption rate in a detritivore population

The metabolic theory of ecology predicts resource consumption rates of animals from their body mass, but other phenotypic traits might affect individual resource consumption rate. In this paper, we used a hierarchical framework to examine relation- ships between phenotypic traits thought to constrain variation in per capita resource consumption rate. Physiological and behavioural traits were assumed to be impor- tant in mediating the control of morphology and sex on consumption. We conducted a longitudinal study aiming to relate the consumption rate of submerged leaf litter to sex, morphological, physiological and behavioural traits in an aquatic detritivore population. Then, we analysed the pattern of trait covariation using structural equa- tion modelling (SEM). We observed broad and repeatable inter-individual variation in leaf consumption rate and other phenotypic traits. We found that expressing litter consumption rate relative to the time individuals spent feeding revealed and increased the effect of body mass and sex differences, respectively. Accordingly, SEM analyses showed that time allocated to resource acquisition mediated body mass and sex effects on apparent litter consumption rate whose variation was also accounted for by an indicator of activity-specific metabolic rate. Substantial variation in resource consump- tion rate was due to sex difference whereas body mass was of secondary importance. Individual phenotypic trait variations strongly altered consumer–resource relation- ships. Therefore, we encourage studies on consumers’ intraspecific variability to advance knowledge about phenotypic determinants of individual resource consump- tion, an important link between individuals and ecosystems.