Does isolation from conspecifics have an effect on pollinator visitation? Some studies have shown that pollinators favor bigger patches of flowering plants. However, other studies have found that isolated plants are more frequently visited by pollinators, perhaps because they experience less intraspecific competition for pollinators. We are interested in this question because of the potential for pollinator visitation to affect the fitness of rare plant species within ecological restorations. We studied how pollinator visitation varies with conspecific density in three species of plants, Penstemon digitalis (beardtongue), Monarda fistulosa (beebalm), and Eryngium yuccifolium (rattlesnake master) within a restored tallgrass prairie. Individuals of these species were mapped within the prairie, and we recorded the number and identity of pollinators that visited these plants. We then tested whether distance to the nearest conspecific plant predicted the rates that pollinators visited these plants.
Results/Conclusions
Our results indicate that plant density is not an important predictor of pollinator visitation to P. digitalis M. fistulosa (p>0.1), but plant density did lead to weak positive effects on pollinator visitation for E. yuccifolium (p=0.0005, r2=0.07). For all species, taller plants with larger inflorescences had greater pollinator visitation rates, and the effect of height and inflorescence size were better predictors than plant density (p<0.001, r2=0.22-0.75). Other studies have reported both positive and negative effects of conspecific density on visitation by pollinators. However, we find that conspecific density is a relatively weak predictor of pollinator visitation rates, and characteristics of the focal plant, including height and inflorescence size, are better predictors of pollinator visitation rates.