High abundance but low diversity of floral visitors on invasive Heracleum mantegazzianum (Apiaceae)

Abstract

Currently, plant invasions affect native ecosystems across the Earth. Although much attention has al -ready been paid to their effect on local communities, we still lack basic information on the associationsbetween alien and local species. Here, we present the results of our survey of pollinators of the invasiveplant Heracleum mantegazzianum (Apiaceae) in central Europe. At 20 sites within the westernmost partof the Czech Republic, which is strongly affected by the invasion of H. mantegazzianum, pollinators onthe flowers of H. mantegazzianum were examined and compared to the species composition of pollinatorson native vegetation in the surrounding area. While the flowers of H. mantegazzianum were frequentlyvisited by high abundance of insects, the communities of H. mantegazzianum pollinators were relativelyspecies poor, and the proportion of abundances of H. mantegazzianum pollinators was very uneven, withfew species of generalist Diptera and the honey bee (Apis mellifera) dominating over all other flower visi-tors. Significantly larger species of the family Syrphidae visited flowers of giant hogweed than of otherplants. Thus, giant hogweed is not a necessary part of flower communities for flower visiting insects, andit should be eradicated because of its negative effects on other plants, landscape and humans. Our resultshighlight the need for more detailed studies on direct interactions between alien plant species and nativepollinator communities as well as indirect interactions between alien plants and native plants throughcompetition for pollinators.