Generalist foraging of pollinators: diet expansion at high density

Authors

  • Colin Fontaine,

    Corresponding author
    1. BioEmCo – UMR 7618, Ecole Normale Supérieure, 46 rue d’Ulm, F-75230 Paris cedex 05, France; and
    2. NERC, Center for Population Biology, Division of Biology, Imperial College London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, UK
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    • These two authors contributed equally to the work.

  • Carine L. Collin,

    1. BioEmCo – UMR 7618, Ecole Normale Supérieure, 46 rue d’Ulm, F-75230 Paris cedex 05, France; and
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    • These two authors contributed equally to the work.

    • Present address: E-mail: cl.collin@gmail.com.

  • Isabelle Dajoz

    1. BioEmCo – UMR 7618, Ecole Normale Supérieure, 46 rue d’Ulm, F-75230 Paris cedex 05, France; and
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Correspondence author. E-mail: c.fontaine@imperial.ac.uk

Summary

  • 1Plant–pollinator interactions are crucial for the reproduction of most angiosperms. When faced with perturbations, plant–pollinator networks might be robust mainly due to the presence of highly generalist species. Perturbations can, in turn, affect how pollinators exploit their food sources and therefore their degree of generalization.
  • 2In particular, generalization of pollinators might vary with forager density. At high densities floral resources available in plant communities would be more rapidly depleted than at low densities. According to optimal foraging theory (OFT), this decrease in resources should lead to an increase in diet breadth.
  • 3We investigated the impact of pollinator density on diet breadth of Bombus terrestris. We recorded the individual foraging behaviour of bumblebees from eight colonies. They foraged in presence of either one or several conspecifics on experimental plant communities composed of five plant species. Diet breadth was calculated as the number of plant species visited, as well as by the Levins index. We analyzed the effect of forager density on diet breadth at both the individual and the colony levels.
  • 4We found that forager density affected degree of generalization at individual and colony levels. A more competitive environment increased individual generalization, as predicted by OFT, and decreased the variability in generalization across colonies. Moreover, we found that bumblebee size was positively related to the amplitude of diet breadth change.
  • 5Synthesis. Our study sheds light on an additional level of complexity of plant–pollinator systems, showing that pollinator diet breadth is a flexible trait which results from behavioural adaptation to resource availability. More generally, changes in foraging insects’ diet via competition for resources are likely to ensue from anthropogenic ecosystem disturbance and to impact upon the functioning of plant–pollinator networks.

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