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Competition for pollinators destabilizes plant coexistence

Abstract

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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Fig. 1: Hand pollination reveals the effects of competition for pollinators on plant coexistence.
Fig. 2: Effects of competition for pollinators on niche and average fitness differences.
Fig. 3: Effects of competition for pollinators on parameter estimates.
Fig. 4: Effects of experimentally simulated pollinator decline on floral visitation and plant per capita population growth.

Data availability

Data are available on Zenodo: https://doi.org/10.5281/zenodo.6474018. The data were recorded in Microsoft Excel (v. 16.48) and analysed in R (v. 3.6.3). Source data are provided with this paper.

Code availability

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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Acknowledgements

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.

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Contributions

C.A.J. and J.M.L. designed the research. C.A.J. performed the experiments and analysed the data. P.D. and C.A.J. conducted the pollinator observations. C.A.J. and J.M.L. wrote the manuscript.

Corresponding author

Correspondence to Christopher A. Johnson.

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The authors declare no competing interests.

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Nature thanks Peter Chesson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Table 1 Details about the annual plant species used in the experiment
Extended Data Table 2 Likelihood-ratio tests evaluating whether low-density fecundity, λi, or competition coefficients, αij, differed between pollination treatments
Extended Data Table 3 Effects of plant competitors for pollinators at multiple spatial scales on pollen limitation
Extended Data Table 4 Effects of pairwise competition for pollinators in all possible three-, four-, and five-species communities

Supplementary information

Supplementary Information

This file contains Supplementary Methods; Supplementary Discussion; Supplementary Tables 1–4 and Supplementary References.

Reporting Summary

Supplementary Fig. 1

Supplementary Data

This file contains source data for Supplementary Fig. 1.

Source data

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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

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