Host energetics explain variation in parasite productivity across hosts and ecosystems

Parasites are thought to play a role in ecosystem energetics, in part because some ecosystems harbor a substantial amount of parasite biomass. Nevertheless, the extent to which parasite biomass accurately reflects the flow of energy from hosts to parasites, and the linkages between their energetics, remain unclear. Here, we estimate parasite community energetics at the host and ecosystem-level and test predictions for parasite energetics using the metabolic theory of ecology. Across 27 host species, parasite community abundance declines with average individual parasite energy use Rp as Rp-0.50 and increases with host metabolic rate Rh as Rh 0.63, which is inconsistent with metabolic theory. We next test whether the fraction of host energy that is allocated to parasitism is invariant across hosts. Our empirical analysis demonstrates that 85% of the variation in parasite community energy use can be explained by differences in host metabolic rate. However, parasite community energy use inc...