There is conflicting research regarding how conspecific density can affect flower pollination, with some studies demonstrating that increased flower density will increase pollinator visitation, and others showing a more negative relationship. This aspect of pollinator behavior is still not fully understood, particularly in how it can affect flowering communities. Pollinator limitation can lead to pollen limitation, harming the viability of affected plant species. This is especially relevant in restorations, since small, isolated patches of flowers can come about due to the unpredictability of restored plant communities. This study investigated how conspecific density effects pollinator visitation in a restored prairie to better understand pollinator behavior and the impact it could have on flowering plants. Three species, Penstemon digitalis, Monarda fistulosa, and Eryngium yuccifolium, were used to determine if isolation from conspecifics would result in a positive or negative impact on pollinator visitation rates. Visiting pollinators were recorded and identified, while GIS was used to quantify the spatial effects that could impact visitation, including both surrounding conspecific density as well as distance from the individual plants to the edge of the nearby forest. Seeds were also collected and weighed from E. yuccifolium to determine if they were pollen limited.
Results/Conclusions
Density of conspecifics did not have an effect on pollinator visitation in P. digitalis (p = 0.12) or M. fistulosa (p = 0.09). However, conspecific density did have a slight positive effect on visitation rates in E. yuccifolium (p = 0.0002 and R2 = 0.08). A majority of the bee species found to be visiting these plants consisted of forest nesting species, presumably from the restored forest bordering the prairie used in this study. However, distance to forest edge did not have an effect on pollinator visitation (P. digitalis = 0.12, M. fistulosa = 0.45, E. yuccifolium = 0.22). These results fall between what other studies have found, with isolation having neither a positive nor negative effect on visitation for two of the study species. Given that higher conspecific density had a positive effect on visitation in E. yuccifolium, it is possible that isolation may only be relevant on a species by species basis. Other factors, such as inflorescence count and plant height, contribute to visitation rates and should be considered in future studies.