Taxonomic and Functional Diversity of the Co-Flowering Community Differentially Affect Cakile edentula Pollination at Different Spatial Scales

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The number of co-flowering species, floral density and floral trait diversity can be major determinants of pollinator-mediated plant–plant interactions in a community. However, evaluation of how each one of these co-flowering components affects the pollination success of a single focal plant species, and how these effects vary at different spatial scales, is lacking. Here, we evaluated the effects of functional diversity (flower morphology and colour), taxonomic diversity (reflecting potential sampling effects) and flower density (conspecific and heterospecific), on the pollinator environment (i.e. visitation rate and pollinator diversity) and pollination success (i.e. pollen load size and number of pollen tubes per style) of Cakile edentula (Brassicaceae). We applied structural equation models (SEMs) at the floral-neighbourhood (plot level) and community-wide scales to uncover the factors that mediate co-flowering community effects on C. edentula pollination success. We found that co-flowering community effects at the community level are more important than fine-scale floral-neighbourhood differences in mediating plant pollination success in our study species. Increasing plant functional diversity decreased pollinator visitation rate but increased the diversity of pollinator functional groups visiting C. edentula flowers. Taxonomic diversity negatively affected pollinator diversity suggesting that other unmeasured floral traits may be relevant or that single-species effects (sampling effects) may be important. Overall, our results suggest that functional floral trait diversity in a community may be the most important factor influencing pollination success of species in a community. We also found evidence for intra- and interspecific pollinator competition mediated by flower density, but none of these effects seemed to have a significant impact on pollination success. This study is an important step towards understanding the complexity of co-flowering community effects on the pollination success of individual plant species at multiple spatial scales. This study further reveals the potential importance of plant functional diversity in a community in helping predict competitive and facilitative interactions in co-flowering communities. Synthesis. Floral density and taxonomic and functional co-flowering diversity are important drivers of pollination success in flowering plants. The effects of the co-flowering diversity on the pollination success of plant species can largely depend on the spatial scale being studied. Only evaluating the outcomes of pollinator-mediated plant–plant interactions at multiple stages of the pollination process can lead to a complete understanding of their ecological consequences in nature.