Importance of big pollinators for the reproduction of two Hypericum species in Cameroon, West Africa

Two woody Hypericum species (H. roeparianum and H. revolutum) often coexist in forest edge and stream mantle communities in the Bamenda-Banoso Highlands, Cameroon. Morphologically nonspecialized flowers of both species are visited by specific eye-catching visitors. Nectarless flowers of H. roeparianum are visited by a large carpenter bee Xylocopa sp. (Hymenoptera) and nectar-producing flowers of H. revolutum are the main source of nectar for sunbirds (Cyanomitra oritis, Cinnyris reichenowi and C. bouvieri). Using a manipulative experiment, we showed that the carpenter bee plays an important role in the reproduction success of H. roeparianum, whereas sunbirds affect seed production of H. revolutum only little. We suggest that a clear differentiation of pollination niches enables the coexistence of both Hypericum species. The study showed that the pollination system of H. roeparianum with morphologically nonspecialized flowers can be ecologically specialized. Sunbirds are not decisive for the reproductive success of H. revolutum and thus have only little selection pressure on its floral traits. The results indicate the importance of reproduction success assessment in pollination studies.