Detection of energetic equivalence depends on food web architecture and estimators of energy use

Ecologists have long debated the universality of the energetic equivalence rule (EER), which posits that population energy use should be invariant with average body size due to negative size–density scaling. We explored size–density and size–energy use scaling across 183 geographically–distributed soil invertebrate food webs to investigate the universality of these fundamental EER assumptions. Additionally, we compared two measures of energy use to investigate size–energy use relationships: population metabolism and energy fluxes. We found that size–density scaling did not support energetic equivalence in soil communities. Furthermore, evidence of energetic equivalence was dependent on the estimate of energy use applied (population metabolism or energy flux), the trophic level of consumers, and food web properties. Our study demonstrates a need to integrate food web energetics and trophic structure to better understand how energetic constraints shape the body size structure of terrestrial ecosystems.