Metabolic rate and foraging behaviour: A mechanistic link across body size and temperature gradients

The mechanistic link between metabolic rate and foraging behaviour is a crucial aspect of several energy-based ecological theories. Despite its importance to ecology however, it remains unclear whether and how energy requirements and behavioural patterns are mechanistically connected. Here we aimed to assess how modes of behaviour, in terms of cumulative space use, patch selection and time spent in an experimental resource patchy environment, are influenced by the foragers’ metabolic rate (SMR) and its main determinants i.e. body mass and temperature. We tested the individual behavioural patterns and metabolic rates of a model organism, the amphipod Gammarus insensibilis , across a range of body masses and temperatures. We demonstrated that body mass and temperature exert a major influence on foraging decisions and space use behaviour via their effects on metabolic rates. Individual cumulative space use was found to scale allometrically with body mass and exponentially with temperature, with patch giving-up time falling as body mass and temperature increased. Moreover, SMR had greater predictive power for behavioural patterns, explaining variation beyond that accounted for by body mass and temperature combined. Our results showed that cumulative space use scaled positively with Mass- and-Temperature-independent SMR (residual). Furthermore, the foraging decisions regarding patch choice and partitioning were strongly related to M-T independent SMR; individuals with higher M-T independent SMR initially preferred the most profitable patch and, as time progressed, abandoned the patch earlier compared to others. Our findings regarding the mechanistic relationship between behavioural patterns and metabolic rate across body mass and temperature shed light on higher-order energy-based ecological processes, with implications in the face of climate change.