Facilitative pollinator sharing decreases with floral similarity in multiple systems

Authors: HA, MELISSA - Mohave Community College, Neal, Campus-Kingman; Schneider, Scott; ALDER, LYNN - University Of Massachusetts

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2020
Publication Date: 10/10/2020
Citation: Ha, M.K., Schneider, S.A., Alder, L.S. 2020. Facilitative pollinator sharing decreases with floral similarity in multiple systems. Oecologia. 195(2):273-286. https://doi.org/10.1007/s00442-020-04770-1.
DOI: https://doi.org/10.1007/s00442-020-04770-1

Interpretive Summary: Many flowering plants rely on insects for pollination. When different flowering plants live in close proximity they interact with one another, either competing for pollinators or facilitating pollinator sharing. This study aims at predicting interactions (competitive or facilitative) between neighboring plants depending upon (1) how closely related they are and (2) the similarity of their flowers. We found that competition increased between closely related plants but not due to the similarity of floral traits that we measured. The majority of species pairs in our study facilitated pollinator sharing. Identifying predictors of the outcome of plant interactions, as was done in this study, can inform the management of rare and invasive species. This information will be useful to ecologists, conservation scientists, and wildlife management agencies.

Technical Abstract: Premise of the study: Since both competition and facilitation shape evolution and community structure, understanding what determines whether interactions are competitive or facilitative elucidates their impacts. Co-flowering plants interact indirectly through shared pollinators, and meta-analyses suggest that phylogenetic relatedness and similarity in floral traits may predict the outcome of these interactions. Using a novel comparative approach in which we manipulated the floral community across five systems, we examined whether closely related and florally similar plants were more likely to compete for pollinators. Methods: To assess pollinator-mediated interactions, we measured pollinator visitation, pollinator behavior, and pollen limitation in each focal species growing alone, with congeners (when available), or with floral neighbors from a different family. We measured floral morphology, color, and nectar traits to calculate multivariate floral similarity between species pairs and inferred a phylogeny from which we calculated phylogenetic distance. Key results: We found that competitive interactions increased with phylogenetic relatedness in four out of five systems, but this relationship was not mediated by the floral traits measured in this study. Pollinator sharing in 11 of the 13 species pairs was facilitative. Conclusions: Our results suggest that facilitative pollinator sharing is more common than reported in the literature. Additionally, we found that closely related, co-flowering plant species are generally likely to compete for pollinators. This relationship warrants further investigation across more plant species. Identifying predictors of the outcome of biotic interactions as was done in this study can inform the management of rare and invasive species.