Larger species tend to feed on abundant resources, which nonetheless have lower quality or degradability, the so-called Jarman-Bell principle. The "eat more" hypothesis posits that larger animals compensate for lower quality diets through higher consumption rates. If so, evolutionary shifts in metabolic scaling should affect the scope for this compensation, but whether this has happened is unknown. Here, we investigated this issue using termites, major tropical detritivores that feed along a humification gradient ranging from dead plant tissue to mineral soil. Metabolic scaling is shallower in termites with pounding mandibles adapted to soil-like substrates than in termites with grinding mandibles adapted to fibrous plant tissue. Accordingly, we predicted that only larger species of the former group should have more humified, lower quality diets, given their higher scope to compensate for such a diet. Using literature data on 65 termite species, we show that diet humification does increase with body size in termites with pounding mandibles, but is weakly related to size in termites with grinding mandibles. Our findings suggest that evolution of metabolic scaling may shape the strength of the Jarman-Bell principle.

Entomology Program National Institute for Amazonia Research Av André Araújo 2 936 Petrópolis Manaus AM CEP 69067 375 Brazil

Faculty of Agrarian Sciences Federal University of Amazonas Av General Rodrigo Octavio Jordão Ramos 1200 Coroado 1 Manaus AM CEP 69067 005 Brazil

Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcká 129 165 00 Praha 6 Suchdol Czech Republic

Federal Institute for Education Science and Technology of Amazonas Estr Coari Itapeua s n Itamarati Coari AM CEP 69460 000 Brazil

Roraima Research Nucleus National Institute for Amazonia Research R Cel Pinto 315 Centro Boa Vista RR CEP 69301 150 Brazil

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