Orchid bees enhance seed set production of an understory herb in the Western Brazilian Amazon

Bee pollination is an important ecosystem service related to the maintenance of many flowering plants. We evaluated the relationship between orchid bee foraging time and the density of flowering plants and whether visitation varied according to the sex and size class of bees, using Calathea mansonis as a model species. We monitored 10 plots between December 2009 and November 2010 in a forest fragment in Senador Guiomard, Acre, Brazil. We counted the number of flowering plants and flowers per plant and the behaviour of the observed bees. Additionally, we compared the bagged and exposed inflorescences for self-compatibility analysis. We sampled 173 orchid bees from 13 species, with Eulaema cingulata as the most abundant visitor. Eulaema (large bees) were more effective pollinators than Euglossa (small bees). We also found Eulaema polyzona individuals feeding on a Marantaceae species for the first time. The time spent by the bees visiting flowers did not differ with the density of flowering plants or the number of flowers per plant. However, flowers exposed to visitors produced 35% more seeds and 15% heavier seeds than bagged flowers. Considering plant–bee interactions, orchid bees may increase gene flow and compensate for the clonal reproduction of this herb.