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Structure and mechanism of diet specialisation: testing models of individual variation in resource use with sea otters

Authors

  • M. Tim Tinker,

    Corresponding author
    1. U.S. Geological Survey, Western Ecological Research Center, Long Marine Lab, 100 Shaffer Rd., Santa Cruz, CA 95060, USA
      E-mail: ttinker@usgs.gov
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  • Paulo R. Guimarães Jr,

    1. Departamento de Ecologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP 05508-900, Brazil
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  • Mark Novak,

    1. Department of Ecology and Evolutionary Biology, University of California, Long Marine Lab, 100 Shaffer Rd., Santa Cruz, CA 95060, USA
    2. Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA
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  • Flavia Maria Darcie Marquitti,

    1. Departamento de Ecologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP 05508-900, Brazil
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  • James L. Bodkin,

    1. U.S. Geological Survey, Alaska Science Center, 4210 University Dr., Anchorage, AK 99508, USA
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  • Michelle Staedler,

    1. Monterey Bay Aquarium Sea Otter Research and Conservation, 886 Cannery Row, Monterey, CA 93940, USA
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  • Gena Bentall,

    1. Monterey Bay Aquarium Sea Otter Research and Conservation, 886 Cannery Row, Monterey, CA 93940, USA
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  • James A. Estes

    1. Department of Ecology and Evolutionary Biology, University of California, Long Marine Lab, 100 Shaffer Rd., Santa Cruz, CA 95060, USA
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E-mail: ttinker@usgs.gov

Abstract

Ecology Letters (2012) 15: 475–483

Abstract

Studies of consumer-resource interactions suggest that individual diet specialisation is empirically widespread and theoretically important to the organisation and dynamics of populations and communities. We used weighted networks to analyze the resource use by sea otters, testing three alternative models for how individual diet specialisation may arise. As expected, individual specialisation was absent when otter density was low, but increased at high-otter density. A high-density emergence of nested resource-use networks was consistent with the model assuming individuals share preference ranks. However, a density-dependent emergence of a non-nested modular network for ‘core’ resources was more consistent with the ‘competitive refuge’ model. Individuals from different diet modules showed predictable variation in rank-order prey preferences and handling times of core resources, further supporting the competitive refuge model. Our findings support a hierarchical organisation of diet specialisation and suggest individual use of core and marginal resources may be driven by different selective pressures.

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