In animal-pollinated plants, pollination success depends critically on the ability to attract effective pollinators. The attractiveness of a given plant, however, can depend both on its own floral traits and flowering phenology as well as the abundance and composition of co-flowering species in the community. Co-flowering species that rely on shared pollinators may compete for visitors, leading to decreased conspecific pollen deposition rates, or receipt of the wrong pollen when pollinators switch between species, leading to increased heterospecific pollen deposition rates. While studies have focused on variation in pollination success in relation to either intraspecific floral variation or community composition, few have investigated their relative importance. Here we examine the pollination success of the annual herb, Oenothera fruticosa across a flowering season. We followed the fates of ~200 individual Oenothera plants across the season and measured floral traits (petal size, style length), plant-level traits (number of open flowers, date of first flower, synchrony with population), and community traits (relative floral abundance of all species in bloom within a 1m radius of focal plants). We evaluated the relative roles of floral traits and community context on pollinator visitation rates, visitor composition, pollen deposition, and seed set.
Results/Conclusions
Both conspecific (mean 879 ±804SD grains per stigma) and heterospecific (mean 350 ±477SD grains per stigma) pollen receipt varied widely across individual flowers, the proportion of heterospecific pollen received was relatively high, but also varied substantially (mean 31.9% ±22.5%SD). Preliminary analyses suggest a positive relationship between the proportion of heterospecific flowers in 1m radii around focal plants increases the proportion of heterospecific pollen deposited. Additionally, seed set for focal plants was positively correlated to the proportion of conspecifics in the 1m radius patches. Floral traits had less consistent impacts on pollen deposition and seed set. Our results suggest that the community composition around individual O. fruticosa plants has significant impacts on their pollination success and may be more important than our measured floral traits.