Fatores que determinam a predação por Bruchinae (Coleoptera chrysomelidae) em sementes das palmeiras simpátricas Attalea apoda Burret e Acrocomia aculeata (jacq.) Lodd. Ex. Martius (Arecaceae)

Abstract

Large part of the seeds produced by plants are lost by predation. This ecological and evolutionary force affects distribution patterns and the abundance of plant communities. Seed predation caused by vertebrates and invertebrates can occur before or after dispersal. The main predators among insects belong to the subfamily Bruquinae, which includes the pachymerini tribe that attack exclusively seeds from palm trees (Arecaceae family). The predation rates in natural populations of palm trees are affected by density-dependent factors such as resource concentration, the presence of an alternative host species, and intra- and interspecific interactions. Thus, the use of phylogenetically close hosts that occur in sympatry can provide robust results about the factors that influence predation rates and host selection by predator insects. Therefore, the aim of this study were to test: first, the resource concentration hypothesis; second, the co-occurrence hypothesis. And third, the host preference hypothesis. To verify the effect of fruit concentration on the proportion of fruits predated, was correlated the seed density and predation rate. To test the co-occurrence, was correlated the predation rate in the pure stands and compared to the predation rate in the heterogenic stand. The preference of host was tested using a multiple-choice arena. Or result show no relation among the density of seeds pós-dispersed and the rate of seeds preyed by bruquid beetles. But there is a positive correlation among the number of eggs oviposited by bruquid beetles and the density of seeds under the palm three. We found significant differences on predation rates among estands; the fruits of A. aculeata palm have high predation rates on the heterogeneous estands than pure stand but A. apoda palm showed less predation rates on heterogeneous estands than pure estand. In laboratory experiment, we found that bruquid beetle attacked A. apoda palm seeds more frequently than A. aculeata palm seeds. Or results indicate that density is not a determinant factor that affects the predation rates caused by bruquid beetles. But the female oviposit more eggs in patches with high fruits density. This behavior indicate a reproductive investment in these patches. In the heterogeneous stand, the greater abundance and fruits of A. aculeata may have contributed to a higher frequency of encounter between fruits of this species and their predators, thus increasing the proportions of predation in fruits of this species in this areas, conferring an indirect protection to fruits of A. apoda.