Co-Blooming Neighbor Plant Diversity and Floral Display Color Similarity Associated with Higher Flower Visitation to Focal Species

Visitation to the flowers of a plant species by potential insect pollinators may be affected by a variety of ecological factors, including the presence of co-blooming heterospecific plants. These indirect interactions, termed associational effects, may be positive or negative and may depend on number of species or density of the co-blooming neighbors or specific traits of these plants. We conducted an observational study of insect visitation to beebalm (Monarda fistulosa) flowers with varying numbers and species identity of co-blooming flowers in areas of tallgrass prairie vegetation in southeastern Wisconsin in order to test our hypotheses that species diversity of co-blooming neighboring plants would positively affect insect visitation to the focal species and that the presence of neighbors with similarly colored floral displays to the focal species would additionally have a positive effect on visitation. We constructed linear mixed-effects models (LMMs) to assess how visitation, particularly by bumblebees (Bombus spp.), to M. fistulosa varied with the diversity of close spatially associated neighbors and display color of those neighbors. We found a significant positive effect of neighbor diversity and richness on insect visitation to focal species flowers, which was more significant when examining only Bombus spp. visitors. We found a marginally significant positive effect of neighbor color similarity to focal species flowers on Bombus spp. visitation but no effect of color similarity when accounting for visitors of all taxa. These results show that both the diversity of neighbors and the similarity of their traits could potentially increase visitation rates to a focal plant species.