Specialization of pollination systems of two co-flowering phenotypically generalized Hypericum species (Hypericaceae) in Cameroon

The degree of specialization in plant-pollinator relationships is probably the most intensively discussed topic of pollination biology. Phenotypically generalized flowers are typically also considered to be generalized ecologically and/or functionally. Our study focuses on visitors to flowers of Hypericum roeperianum and H. revolutum, two closely related co-flowering Afromontane plants with flat flowers, which can be visited by many insects. We collected insect visitors and recorded their behaviour. Both Hypericum species were visited by large numbers of morphospecies and functional groups, which might indicate that they are highly generalized plants. Nevertheless, after including the visitors' abundance, behaviour and contact with the plants' reproductive organs, only a single carpenter bee species could be considered an effective pollinator of H. roeperianum, and a few smaller bee species (mainly Apis mellifera and Meliplebeia ogouensis) could be considered as effective pollinators of H. revolutum. Despite the fact that the flowers appear at first glance phenotypically generalized, both species seem to be ecologically and functionally specialized for bee pollination. Our results indicate that even phenotypically generalized flowers can be functionally and ecologically specialized. More precise knowledge of their visitors' behaviour is crucial for understanding their pollination systems. Our results cast doubts upon the currently leading opinion that generalization prevails in pollination systems, as such conclusions are based mainly on community-wide studies, which usually do not consider the true role of insect visitors.