Herbivore impact on grassland plant diversity depends on habitat productivity and herbivore size

Authors

  • Elisabeth S. Bakker,

    Corresponding author
    1. School of Biological Sciences, University of Nebraska, 348 Manter Hall, Lincoln, NE 68588-0118, USA
    2. Department of Plant–Animal Interactions, Netherlands Institute of Ecology (NIOO-KNAW), Rijksstraatweg 6, NL-3631 AC Nieuwersluis, The Netherlands
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  • Mark E. Ritchie,

    1. Department of Biology, Syracuse University, 130 College Place, Syracuse, NY 13244-1270, USA
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  • Han Olff,

    1. Community and Conservation Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 14, NL-9750 AA Haren, The Netherlands
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  • Daniel G. Milchunas,

    1. Forest, Range and Watershed Stewardship Department, Colorado State University, Ft Collins, CO 80523, USA
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  • Johannes M. H. Knops

    1. School of Biological Sciences, University of Nebraska, 348 Manter Hall, Lincoln, NE 68588-0118, USA
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* E-mail: l.bakker@nioo.knaw.nl

Abstract

Mammalian herbivores can have pronounced effects on plant diversity but are currently declining in many productive ecosystems through direct extirpation, habitat loss and fragmentation, while being simultaneously introduced as livestock in other, often unproductive, ecosystems that lacked such species during recent evolutionary times. The biodiversity consequences of these changes are still poorly understood. We experimentally separated the effects of primary productivity and herbivores of different body size on plant species richness across a 10-fold productivity gradient using a 7-year field experiment at seven grassland sites in North America and Europe. We show that assemblages including large herbivores increased plant diversity at higher productivity but decreased diversity at low productivity, while small herbivores did not have consistent effects along the productivity gradient. The recognition of these large-scale, cross-site patterns in herbivore effects is important for the development of appropriate biodiversity conservation strategies.

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