Influences of trait similarity of neighbors on pollinator assemblages visiting a native plant species

Associational or neighborhood effects in plant-insect ecology describe the ways neighboring species may indirectly influence the pollination or herbivory of a nearby focal plant. Neighboring species can facilitate pollination for a focal species or may compete for pollinators, yet these effects can be highly variable in ways that are currently difficult to predict. Floral neighborhoods have also been observed to influence the pollinator assemblages that visit a focal species; however, how specific floral traits of neighboring species may affect the pollinator assemblage of a species is not well understood. Our study used Monarda fistulosa, or common beebalm, a perennial herb common in temperate grasslands of North America pollinated primarily long-tongued bees, as our focal plant species. We quantified community weighted mean floral traits of the plant community surrounding each focal M. fistulosa at multiple prairie sites in southeastern Wisconsin. We observed patterns of visits to M. fistulosa with regards to the surrounding flower species. We found that similarity of the community traits to the focal species affected the abundance and composition of insects visiting flowers of M. fistulosa, and that dominance of M. fistulosa determined whether this effect was competitive or facilitative. Our results imply that trait similarity and relative dominance are integral to associational effects in plant-pollinator interactions with implications for understanding population and community dynamics.