Efeito do isolamento e perda de área de floresta sobre populações de saúvas (hymenoptera, formicidae, atta) e seus inimigos naturais em ilhas do Reservatório da UHE Balbina, Amazônia central, Brasil

Abstract

The habitat fragmentation affects the trophics levels in different ways. I evaluated the effect of islands creation in a reservoir of hydroelectric power plant of Balbina (Central Amazonia) on the populations of leaf-cutting ants Atta spp. and its natural enemies. I hypothesize that there is a reduction in the abundance, or even exclusion, of parasitoids and predators in the islands, leading to an increase of the leaf cutting ants populations and a decrease in the nests' size. I measured the densities and size of leaf-cutting ant nests, and the abundance of parasitoids phorid flies, and armadillos. The occurrence of army ant colonies in 25 islands of 2-3 ha, and 28 in transects of 1 ha installed in a continuous forest in the neighborhoods of the Reservoir of Balbina was registered. The mean density of leaf-cutting ant nests in islands was 2.5-fold higher - compared to the continuous forest. The relative abundance of phorid flies and armadillos was similar between the two habitats. Army ants were not detected in the islands, but three species were found in the continuous forest. The average sizes of the leaf-cutting ants nest in the two sites were equally elevated. Therefore, because of the highest density registered in the islands, the ant nests occupied an area more than two times larger in this habitat in comparison to the continuous forest (14% versus 6%, respectively). Although I did not find relation among density of ant nests with the abundance of phorid flies and armadillos, their role as population regulators of leaf-cutting ants do not have to be discarded.