Warming alters consumption efficiency of terrestrial arthropods

Metabolic theory predicts that the external temperature determines metabolism. As the energy loss to metabolism needs to be balanced by energy gain, it is likely that consumption is similarly constrained by temperature. For the first time, we studied temperature dependence of metabolism and consumption of differently-sized prey species by ground-dwelling beetles and spiders. While warming increased the metabolic rates substantially, the feeding rates generally increased less. Additionally, we found that the temperature-dependence of the feeding rates depended on the body mass-ratio of the predator to the prey: they increased only if the prey is of optimal size for the capture success of the predator, whereas they did not change if the prey was smaller. Moreover, the feeding rates of optimally-sized prey increased less with temperature than the metabolic rates. Together, these results suggest that the predators studied are subject to severe energy limitation under warming. These results have profound implications for (1) temperature-dependent population dynamics, (2) energy transfer to higher trophic levels and (3) predictions on the consequences of global warming.