The floral neighborhood, or community of co-flowering plants surrounding an individual plant, could influence plant reproduction by affecting pollination. Plants in highly fragmented habitats already risk poor reproduction due to mate-limitation, so understanding how community dynamics further impact reproduction is especially critical. To gain a mechanistic understanding of how floral neighborhood influences reproduction in a fragmented landscape, we characterized the floral neighborhood surrounding 224 flowering Echinacea angustifolia (a common tallgrass prairie perennial) individuals, including richness and diversity of heterospecifics, and proximity to potential conspecific mates. We then quantified Echinacea pollen flow by conducting 795 pollinator observations, and observing the abundance and diversity of pollen on both pollinators and Echinacea stigmas. We tested:1) how floral neighborhood influences pollinator visitation rates, 2) how much pollen loads differ among pollinator taxa, 3) how floral neighborhood influences pollen deposition on stigmas, and 4) how floral neighborhood influences reproductive success of Echinacea.
Results/Conclusions
First, we found that floral neighborhood (as described by Shannon’s diversity, species richness, and Echinacea’s isolation from potential mates) influences pollinator visitation rate. Plants with highest visitation rates (> 60%) were found in two scenarios, either surrounded by high floral richness (> 6 co-flowering species) and isolated from mates (> 9m from second nearest flowering Echinacea) or surrounded by low floral richness (< 2 co-flowering species) and very close to potential mates (< 2m from second nearest flowering Echinacea). Second, we found pollen abundance on pollinators (p < 0.0001) but not richness (p=0.18) differed among pollinator taxa, suggesting a few differences in foraging amongst the 8 observed generalist pollinator taxa (average pollen richness was approximately 1.5 pollen morphospecies per pollinator taxa). Third, we found conspecific pollen abundance on stigmas declined as floral neighborhood richness increased (p = 0.03) and heterospecific pollen abundance increased with Shannon’s diversity (p = 0.04). Fourth, we found the highest levels of reproductive success for Echinacea individuals that were less isolated from mates and surrounded by higher floral diversity. Taken together, these results suggest floral neighborhood affects Echinacea reproductive success through mediating impacts on pollen flow.