Trap size and prey selection of two coexisting bladderwort (Utricularia) species in a pristine tropical pond (French Guiana) at different trophic levels

Abstract

An analysis of the morphology and the prey consumed by two carnivorous species of bladderworts (Utricularia gibba and U. sp.2) from a pond (Annie pond) in the heart of the Kaw swamp (French Guiana) has allowed a comparison of the preferential prey of: 1) a single species over two different periods (the end of the rainy season and the beginning of the dry season during an oligotrophic phase); and 2) the two coexistent species within a single period (the beginning of the dry season, during a temporary mesotrophic phase). Among the immediately adjacent planktonic and periphytic animals, and despite their low prevalence relative to smaller organisms such as Gastrotricha and Rotifera, cladocerans and copepods (particularly large individuals) appeared to be strongly predated. The differing organization and size-class distributions of the traps, as well as the extent of epiphytic colonization, had a probable defining effect on the alimentary regime of the two species of Utricularia. These more or less adaptive characteristics allowed the bladderworts to take advantage of the distinct preferences of various potential prey in terms of nutrition behaviour and habitat so to limit the feeding competition between the two sympatric species. The impact of this selective zooplankton predation by bladderworts on the trophic organization and the ecological functions of this pond are also addressed.