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Foraging constraints reverse the scaling of activity time in carnivores

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The proportion of time an animal spends actively foraging in a day determines its long-term fitness. Here, we derive a general mathematical model for the scaling of this activity time with body size in consumers. We show that this scaling can change from positive (increasing with size) to negative (decreasing with size) if the detectability and availability of preferred prey sizes is a limiting factor. These predictions are supported by a global dataset on 73 terrestrial carnivore species from 8 families spanning >3 orders of magnitude in size. Carnivores weighing ∼5 kg experience high foraging costs because their diets include significant proportions of relatively small (invertebrate) prey. As a result, they show an increase in activity time with size. This shifts to a negative scaling in larger carnivores as they shift to foraging on less costly vertebrate prey. Our model can be generalized to other classes of terrestrial and aquatic consumers and offers a general framework for mechanistically linking body size to population fitness and vulnerability in consumers.

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Fig. 1: Size-scaling model of activity time in terrestrial carnivores.
Fig. 2: Observed size-scaling of the energy intake rate and activity proportions among carnivores.
Fig. 3: Scaling of intake rate and prey versus predator size (size ratio) among carnivores.

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We thank V. Muggeo and D.-G. Kontopoulos for advice on the phylogenetically independent contrast and phylogenetic piecewise regression analyses. S.P. was supported by grant NE/M004740/1 awarded by the Natural Environmental Research Council and the Grand Challenges in Ecosystems and the Environment Initiative at Imperial College London.

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M.R., C.C. and S.P. designed the study. S.P. developed the mathematical model. M.R. performed the data compilation and analyses and wrote the first draft of the paper. All authors substantially revised the paper.

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Correspondence to Matteo Rizzuto or Samraat Pawar.

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Rizzuto, M., Carbone, C. & Pawar, S. Foraging constraints reverse the scaling of activity time in carnivores. Nat Ecol Evol 2, 247–253 (2018).

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