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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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.

Author information


  1. Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, SL5 7PY, UK

    • Matteo Rizzuto
    •  & Samraat Pawar
  2. Department of Biology, Memorial University of Newfoundland, 230 Elizabeth Avenue, St. John’s, A1B 3X9, Newfoundland and Labrador, Canada

    • Matteo Rizzuto
  3. Institute of Zoology, Zoological Society of London, Regent’s Park, London, NW1 4RY, UK

    • Chris Carbone


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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.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Matteo Rizzuto or Samraat Pawar.

Electronic supplementary material

  1. Supplementary Information

    Supplementary Information, Supplementary Figures 1–10, Supplementary Tables 1–5 and Supplementary References

  2. Life Sciences Reporting Summary