COS 106-8 - Apparent competition through granivores impacts plant coexistence

Wednesday, August 9, 2017: 4:00 PM
C122, Oregon Convention Center
William K. Petry, Institute for Integrative Biology, ETH Zurich, Zürich, Switzerland; Rocky Mountain Biological Laboratory, Nathan J. B. Kraft, Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, Gaurav Kandlikar, Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA, Oscar Godoy, Csic, Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), Sevilla, Spain and Jonathan M. Levine, Institute for Integrative Biology, ETH Zurich, Zurich, Switzerland

Species are predicted to coexist when ecological mechanisms concentrate fitness losses on common species and allow rare species populations to grow. Classically, consumers have been thought to promote coexistence by reducing competitor abundance and the strength of resource competition. However, recent theory shows that consumers may have a much broader range of effects, promoting or inhibiting the coexistence of their prey by restructuring competitive advantages and negative frequency dependence through apparent competition. We tested the role of consumers on the coexistence of their prey in an annual plant community where granivorous ants and rodents reduce plant fitness by consuming seeds. We paired field competition and seed consumption experiments to parameterize a coexistence model for 15 plant species to understand the relative roles of competition and apparent competition in structuring plant biodiversity.


We found that seed consumption rates by generalist granivores differed strongly among our focal plant species. By comparing the coexistence model with and without granivores, we showed that seed consumption has strong impacts on which plant species are predicted to coexist. Granivores enabled some species that would be competitively excluded to stably persist in the community. Other species were predicted to be excluded by competitors or driven to extinction by seed consumption alone when granivores were present. The effects of granivorous ants on plant competitive outcomes were much stronger than those of rodents, indicating that different guilds of herbivores may have markedly different impacts on plant diversity. Taken together, our work provides key evidence to validate the theoretical predictions of how consumers structure communities of their prey.