A influência do tamanho do corpo na qualidade da dispersão de sementes pelo pacu, Piaractus mesopotamicus (HOLMBERG, 1887) (SERRASALMIDAE) em florestas alagáveis do Pantanal Norte

Abstract

Seed dispersal is an ecological process that contributes to structuring plant communities and the maintenance of species diversity. In wetlands seeds are also dispersed by frugivores fish entering the flooded forest during seasonal floods, an interaction known as ichthyochory. The Pantanal is the largest wetland in South America with presence of fruit fish, with featured for the pacu, Piaractus mesopotamicus. Despite the 269 species of fish and high floristic diversity, few studies have evaluated the fish action in seed dispersal in this area. In order to reduce this deficiency, this study has the objectives of: evaluate the frequency and magnitude of the consumption of seeds intact by P. mesopotamicus and its potential as a seed disperser; with the hypothesis that P. mesopotamicus consume fruit throughout the flood season and that this consumption does not compromise the viability of seeds consumed; and evaluate whether of the P. mesopotamicus size influences the effectiveness of the seed dispersal of the plants; with the hypothesis that under P. mesopotamicus individuals are less effective dispersers than the larger, given that initial studies suggest that the efficacy of seed dispersal appear to improve with age and size of fish. I evaluated the diet composition of young and adult fish of this species through the methods of regurgitation and dissection of the digestive apparatus, during the flood period Northen Pantanal. I separated the content diet, quantify and identified the seeds using a stereoscopic microscope and comparisons with botanical samples from inventory conducted in the area. I performed the botanical inventory throughout the sampling plants that were fruitful in the flood season. Submitted seeds intact the germination experiments to test the viability of germination compared with control seeds (i.e., that did not pass by the digestive apparatus of the fish). Considering the nature of the data, for most of the analyses I used Generalized Linear Models (GLMs). With a total the seeds in the diet of 219 individuals of P. mesopotamicus examined represented approximately 42% of the species of plants bearing fruits during the flooded season at the sampled sites. In general, the planting trials validated the viability of many intact seeds found in digestive tratcs of P. mesopotamicus, and demonstrated acelerated germination for Cayaponia podantha and Mendoncia puberula. Length fish limited seed consumption small fish consumed only small seeds, while big fish consumed a larger range of seed sizes, including those of larger sized species. Therefore, the richness and abundance of intact seeds in the diet are associated with P. mesopotamicus body size. In other words, the larger fish are more effective dispersers it consume higher amount of intact seeds and have potential for longest displacements that the smaller and juvenile fish.