Mounting concern over the global decline of pollinators has fuelled calls for investigating their role in maintaining plant diversity1,2. Theory predicts that competition for pollinators can stabilize interactions between plant species by providing opportunities for niche differentiation3, while at the same time can drive competitive imbalances that favour exclusion4. Here we empirically tested these contrasting effects by manipulating competition for pollinators in a way that predicts its long-term implications for plant coexistence. We subjected annual plant individuals situated across experimentally imposed gradients in neighbour density to either ambient insect pollination or a pollen supplementation treatment alleviating competition for pollinators. The vital rates of these individuals informed plant population dynamic models predicting the key theoretical metrics of species coexistence. Competition for pollinators generally destabilized the interactions between plant species, reducing the proportion of pairs expected to coexist. Interactions with pollinators also influenced the competitive imbalances between plant species, effects that are expected to strengthen with pollinator decline, potentially disrupting plant coexistence. Indeed, results from an experiment simulating pollinator decline showed that plant species experiencing greater reductions in floral visitation also suffered greater declines in population growth rate. Our results reveal that competition for pollinators may weaken plant coexistence by destabilizing interactions and contributing to competitive imbalances, information critical for interpreting the impacts of pollinator decline.
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Codes are available on Zenodo: https://doi.org/10.5281/zenodo.6474018. The figures were plotted in Mathematica (v. 12.0).
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We thank M. von Rütte, A. Bieger, C. Hess, M. Negreiros, A. Reid and R. Zäch for their work in the field and laboratory; J. Johnson (Life Science Studios) for the illustrations in Figs. 1 and 3; W. Petry and S. Hart for statistical advice; and laboratory members at the ETH Zürich and Princeton University for comments on the manuscript. C.A.J. was supported by the ETH Zürich Center for Adaptation to Changing Environments and funds from Princeton University. J.M.L. was supported by NSF grant DEB 2022213.
The authors declare no competing interests.
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Johnson, C.A., Dutt, P. & Levine, J.M. Competition for pollinators destabilizes plant coexistence. Nature 607, 721–725 (2022). https://doi.org/10.1038/s41586-022-04973-x