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Pathogens promote plant diversity through a compensatory response

Authors

  • Devon J. Bradley,

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman Street, Box G-W, Providence, RI 02912, USA
    2. Department of Environmental Studies, University of California, 1156 High Street – 405 ISB, Santa Cruz, CA 95064, USA
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  • Gregory S. Gilbert,

    1. Department of Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697, USA
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  • Jennifer B. H. Martiny

    1. Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman Street, Box G-W, Providence, RI 02912, USA
    2. Department of Environmental Studies, University of California, 1156 High Street – 405 ISB, Santa Cruz, CA 95064, USA
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*E-mail: djbradle@uci.edu

Abstract

Pathogens are thought to promote diversity in plant communities by preventing competitive exclusion. Previous studies have focussed primarily on single-plant, single-pathogen interactions, yet the interactions between multiple pathogens and multiple hosts may have non-additive impacts on plant community composition. Here, we report that both a bacterial and a fungal pathogen maintained the diversity of a four-species plant community across five generations; however, significant interactions between the pathogens resulted in less plant diversity when the two pathogens were present than when the fungal pathogen was present alone. Standard models predict that pathogens will maintain plant diversity when they cause a disproportionate loss of fitness in the dominant plant species. In our experiment, however, pathogens maintained plant diversity because the rare species produced more seeds through a compensatory response to pathogen infection. Finally, we found that the influence of pathogens on maintaining plant diversity was 5.5 times greater than the influence of nutrient resource heterogeneity. Pathogens may be a major factor in maintaining plant diversity, and our findings emphasize the importance of investigating the roles of pathogens in natural plant communities.

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