The role of species diversity for ecosystem functioning has been hypothesized as unpredictable (idiosyncratic), monotonically additive (rivet-popping) or redundant after minimum diversity (functional redundancy). We evaluated the contributions of floral visitors of Psychotria suterella to its pollination, applying hypotheses concerning biodiversity and ecosystem function to a plant-pollinator system in a fragmented landscape. Nineteen species of floral visitors were arranged into seven functional groups based on three functional traits, and based on floral visitors' response to habitat fragmentation. Although several species of floral visitors deposited similar amounts of pollen grains per visit, Bombus brasiliensis was responsible for 35% of the observed visits, and was the most important pollinator. Additionally, there was no evidence of compensation in density, since abundance and richness of floral visitors were correlated across the ten populations of P. suterella. Therefore, we did not find evidence supporting the occurrence of functional redundancy in this system, and functional or taxonomic grouping would hardly explain equivalence in pollination effectiveness among the species. Furthermore, the resilience of this generalist system to habitat fragmentation, as suggested by the similar levels of pollination in fragmented and non-fragmented sites, makes P. suterella an important species for restoration initiatives in its natural areas of occurrence.
