Adaptive foraging behaviour increases vulnerability to climate change

Species adaptative foraging behaviour is now widely considered as enhancing species coexistence and hence biodiversity. However, most of the results are based on the hypothesis that species foraging maximises their energetic income, following the principles of optimal foraging theory. We here tested how the foraging behaviour of six fish species from two functional groups that differ by their body shape and hunting strategy responds to local ecosystem productivity and temperature using an allometric framework. We found that at higher temperatures, when the energetic stress of species increases because of their higher metabolic rates, species foraging is more driven by encounter rates than by trait selectivity. Contrary to classical hypotheses, we show that this change in behaviour leads to a lower consumption efficiency as species depart from their optimal trophic niche. We then analyse the consequences of this behavioural adaptation using a dynamic model and show that the incorporation of adaptive behaviour lowers species coexistence in food webs.