LAUSR

There is little understanding of the role of exotic bees in the observed pollinator decline. Recent models of species invasions predict that aggressive species have more impact; applying this theory to pollinators suggests that aggressive territorial Anthidium (Megachilidae) bees, whose range is expanding globally, could have high impacts on native bees. We examined exploitation and interference competition for floral resources between Anthidium and native bees in unmanaged urban meadows in Montreal, Canada. First, we conducted a survey of floral visits by Anthidium and native bee genera. We found high niche overlap with Megachile (Megachilidae), one of the most common genera of native pollinators in the area, suggesting high potential for exploitation competition. Second, we tested for interference competition between Anthidium and Megachile with behavioural observations of foraging on a common introduced host plant (Lotus corniculatus, Fabaceae). This presence of Anthidium decreased patch residence and number of floral visits by Megachile bees, suggesting that Anthidium has a significant per capita effect on foraging behavior of Megachile.