Bumblebee pollination of understorey shrub species in a tropical montane forest in Costa Rica

This study addresses the pollination ecology of shrub species in an upper m ontane forest in Costa Rica, where the diversity of insect visitors is much below that of the well-studied tropical forests of lower elevations. Data are presented on visitation rates by the tropical bumblebee Bombus ephippia tus to flowers of three species, pollen loads on bumblebee bodies, and poll en loads on stigmas of two of` the species. High visitation rates to flower s of Palicourea brenesii were found, a species which produces copious amoun ts of nectar. Visitation rates to nectarless Leandra subseriata and Deppea grandiflora were much lower. Conspecific pollen comprised on average 90% of the pollen load on stigmas of Leandra, while Palicourea stigmas carried on ly 26 to 55% conspecific pollen, With only two ovules per flower, fruit and seed set in Palicourea were not limited by a shortage of conspecific polle n. In Leandra, 20-25% of the flowers received too few conspecific pollen gr ains for maximum seed set among 440 ovules per flower. Individual bumblebee s showed no constancy in plant choice, judging from the high number of diff erent pollen types (6-12) on their bodies. Workers returned frequently to t he same Palicourea patch without visiting nearby Palicourea plants, which s uggests the use of foraging paths.