Pollen flow and pollinator sharing among synchronopatric species of Psychotria (Rubiaceae)

Abstract

Sympatric plant species that flower at the same time in highly seasonal environments are subject to competitive interference. Many species of the genus Psychotria (Rubiaceae) are sympatric and have an aggregated flowering period, which may have a strong influence on interactions among these species and their pollinators. We assessed the strategies of sympatric species of Psychotria to segregate or share pollinators, and the consequences for intra- and interspecific pollen flow. We sampled pollinators and analyzed flowering phenology, floral tube length, pollinator tongue length and floral nectar production of three sympatric species of Psychotria in the understory of a tropical forest in Brazil. We also marked flowers with fluorescent powder to monitor the flow of pollen. The studied species of Psychotria exhibited a short synchronous flowering period, with the sharing of pollinators and interspecific pollen exchange. The prevalence of shared or unshared pollinators and of intra- or interspecific pollen exchange varied among the studied species. Variation in floral tube length and nectar was not enough to hamper the sharing of most pollinators and pollen flow between Psychotria nitidula and P. hoffmannseggiana. Non-shared pollinators were more common in flowers of P. prunifolia, probably due to its longer floral tube, which can impede the access of shared pollinators. The higher offer of floral nectar by P. prunifolia makes this species more attractive to a greater number of flower visitors. Pollinator sharing seems to have no negative effect on intraspecific pollen flow and on the reproductive success of the studied synchronopatric species of Psychotria.