Predicting the effects of body size, temperature and diet on animal feeding rates

1. Consumption rates constitute a fundamental, yet relatively elusive quantity in ecophysiology and ecosystem ecology. Measuring consumption rates of highly mobile animals is often challenging, especially in the wild, which makes scientists rely on proxies such as bite rates. However, we still lack a theoretical framework that formally bridges these quantities. 2. Here we expanded a model based on the Metabolic Theory of Ecology to quantitatively characterise how consumption rates are related to bite rates, and predict how the latter should change with body size, temperature and diet. We test our predictions using mensurative experiments from eight populations of redlip blennies-genus Ophiobiennius-across the Atlantic Ocean. 3. Bite rates scaled with body size according to our theoretical predictions. On the other hand, they increased at a faster-than-predicted rate with rising temperatures. This finding might be explained if the energetic content of Ophioblennius spp. diet-which is primarily composed by detritus across all populations-decreases with temperature. Yet, they seem to be consistent with the idea that populations adapted to warmer environments exhibit higher-than-expected grazing pressure on primary producers. 4. Current ocean warming is set to skew body size distributions towards smaller sizes, and our model indicates that the combined effects of smaller sizes and higher temperatures will increase mass-specific consumption rates, with direct implications for how energy flows through food webs.