Anthidium manicatum, an invasive bee, excludes a native bumble bee, Bombus impatiens, from floral resources.
Anthidium manicatum is an invasive pollinator reaching widespread distribution in North America. Male A. manicatum aggressively defend floral territories, attacking heterospecific pollinators. Female A. manicatum are generalists, visiting many of the same plants as native pollinators. Because of A. manicatum's rapid range expansion, the territorial behavior of males, and the potential for female A. manicatum to be significant resource competitors, invasive A. manicatum have been prioritized as a species of interest for impact assessment. But despite concerns, there have been no empirical studies investigating the impact of A. manicatum on North American pollinators. Therefore, across a two-year study, we monitored foraging behavior and fitness of the common eastern bumble bee (Bombus impatiens) in response to A. manicatum presence. We found that B. impatiens avoided foraging near A. manicatum in both years; but despite this resource exclusion, we found no evidence of fitness consequences for B. impatiens. These results suggest A. manicatum pose as significant resource competitors, but that B. impatiens are likely able to compensate for this resource loss by finding available resources elsewhere.