Abstract
Biological invasions can strongly influence species interactions such as pollination. Most of the documented effects of exotic plant species on plant-pollinator interactions have been observational studies using single pairs of native and exotic plants, and have focused on dominant exotic plant species. We know little about how exotic plants alter interactions in entire communities of plants and pollinators, especially at low to medium invader densities. In this study, we began to address these gaps by experimentally removing the flowers of a showy invasive shrub, Rosa multiflora, and evaluating its effects on the frequency, richness, and composition of bee visitors to co-flowering native plants. We found that while R. multiflora increased plot-level richness of bee visitors to co-flowering native plant species at some sites, its presence had no significant effects on bee visitation rate, visitor richness, bee community composition, or abundance overall. In addition, we found that compared to co-flowering natives, R. multiflora was a generalist plant that primarily received visits from generalist bee species shared with native plant species. Our results suggest that exotic plants such as R. multiflora may facilitate native plant pollination in a community context by attracting a more diverse assemblage of pollinators, but have limited and idiosyncratic effects on the resident plant-pollinator network in general.
Highlights
The introduction of exotic plant species with a showy floral display has the potential to alter plant-pollinator interactions of the resident community
The mean visitation rate of bee visitors to R. multiflora across sites was less than 10% than that of all other native plant species (p,0.05, Fig. 2A), but the diversity of visitors to R. multiflora was .19% higher relative to native plant species (Fig. 2B)
Our results showed that 1) Rosa multiflora was visited by the richest assemblage of bee species of all plants studied, but at the lowest visitation frequency, 2) the presence of R. multiflora did not alter visitation rates or the diversity and composition of visitors to native plant species and 3) R. multiflora received visits from bees with wider diet breadths than expected by chance
Summary
The introduction of exotic plant species with a showy floral display has the potential to alter plant-pollinator interactions of the resident community. A recent meta-analysis reported that overall, exotic plant species tend to negatively affect the pollination and reproductive success of native plant species [1] the presence of exotic plant species can decrease the diversity and abundance of pollinators that occur in the area [2], decrease the pollinator visitation rates observed on native plants [3,4,5], and increase interspecific pollen transfer for native plants [6]. It is possible that the greater support in the literature for negative effects of exotic species on native plant pollination is because researchers have largely focused on communities containing moderate to high densities of exotic plants, where one would expect to see strong effects of exotic plant presence. Investigations of exotic species invasions in habitats where they are not dominant provide additional insight into the spectrum of possible exotic plant effects on native plantpollinator communities
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