A role for indirect facilitation in maintaining diversity in a guild of African acacia ants

Authors

  • Todd M. Palmer,

    1. Center for Population Biology, University of California, Davis, California 95616 USA
    2. Mpala Research Centre, Box 555, Nanyuki, Kenya
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    • Present address: Department of Biology, University of Florida, Gainesville, Florida 32611 USA. E-mail: tmp@ufl.edu

  • Maureen L. Stanton,

    1. Center for Population Biology, University of California, Davis, California 95616 USA
    2. Mpala Research Centre, Box 555, Nanyuki, Kenya
    3. Section of Evolution and Ecology, University of California, Davis, California 95616 USA
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  • Truman P. Young,

    1. Center for Population Biology, University of California, Davis, California 95616 USA
    2. Mpala Research Centre, Box 555, Nanyuki, Kenya
    3. Department of Plant Sciences, University of California, Davis, California 95616 USA
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  • John S. Lemboi,

    1. Mpala Research Centre, Box 555, Nanyuki, Kenya
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  • Jacob R. Goheen,

    1. Mpala Research Centre, Box 555, Nanyuki, Kenya
    2. Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131 USA
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    • Present address: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544 USA.

  • Robert M. Pringle

    1. Mpala Research Centre, Box 555, Nanyuki, Kenya
    2. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 USA
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    • Present address: Departments of Zoology and Physiology and Botany, University of Wyoming, Laramie, Wyoming 82071 USA.


  • Corresponding Editor: D. A. Holway.

Abstract

Determining how competing species coexist is essential to understanding patterns of biodiversity. Indirect facilitation, in which a competitively dominant species exerts a positive effect on one competitor by more strongly suppressing a third, shared competitor, is a potentially potent yet understudied mechanism for competitive coexistence. Here we provide evidence for indirect facilitation in a guild of four African Acacia ant species that compete for nesting space on the host plant Acacia drepanolobium, showing that a competitively dominant acacia ant species indirectly creates establishment opportunities for the most subordinate species that may help to maintain diversity. Using long-term observational data and field experiments, we demonstrate that the competitively dominant ant species outcompetes two competitively intermediate species, while tolerating colonies of the subordinate competitor; this creates opportunities for local colonization and establishment of colonies of the subordinate species within the dominant species' territories. Host plants occupied by this subordinate species are then more likely to be colonized by the intermediate species, which in turn are more likely to be displaced by the dominant species. This process has the potential to generate a cyclical succession of ant species on host trees, contributing to stable coexistence within this highly competitive community.

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