Natural habitats are threatened by invasive species that displacing native plant communities. The majority of flowering plants rely on pollinators – and especially bees – for reproduction. Many studies have been conducted on how the presence of invasive plants affect pollinator behaviour through direct and indirect competition. Here, we examine how dog-strangling vine (DSV) impacts bee diversity and foraging success in an urban park. Dog-strangling vine is a perennial native to Eastern Europe that forms dense monocultures and is invasive in Eastern North America. While the impact of DSV on plant communities is well known, there is no knowledge of how it effects bee community, pollen availability and foraging success. In this study, we investigated the impacts of DSV on plant-pollinator interactions, predicting that DSV directly decreases flower diversity, and the number of interactions between bees and unique pollen types. We sweep-netted eight open meadow sites across a DSV invasion gradient for bees over thirteen collection periods in a single season. Pollen was identified from each bee and using linear regressions and bipartite analyses, we determined the effect of DSV on floral richness and plant-pollinator interactions.
The floral richness of the sites showed a marginally significant decreasing trend with increasing DSV invasion (p<0.1 ;F=5.046). This is a result of DSV’s strong, competitive ability, where it outcompetes native plants for above and below ground space. As DSV invades a habitat, it allocates nutrients to parts responsible for nutrient uptake (roots), increasing its ability to out-compete other plants. A comparison of the number of bee-pollen interactions and DSV invasion showed a significant decrease in interaction abundance with increased invasion (p<0.05 ;11.87). This observation results from fewer floral species with increasing DSV. As floral richness declines over the gradient, there are less flower options for bees to forage on, forcing them to expand their foraging range. As a result, fewer bee-pollen interactions are observed within the more invaded sites.
Our results show that plant-pollinator networks are negatively impacted by invasive plant species. An invasive will out-compete native flora, and change the pollinator community composition, ultimately leading to changes in network structure, and future bee population declines. We conclude that DSV is disturbing native plant-pollinator interactions in urban parks, and management efforts must be implemented to protect parklands from becoming completely invaded, resulting in conditions that accommodate fewer bee species.