The influence of anthropogenic disturbances on the structure of arboreal arthropod communities

In the framework of our research, aimed at understanding the processes stru cturing tropical arthropod communities, we investigated the changes occurri ng in tree crown communities of forests of different disturbance levels. Th ese were a mixed dipterocarp primary lowland rain forest in Kinabalu Nation al Park (in Sabah, Malaysia) and, some kilometres away, three forests of re generation periods 5, 15, and 40 years following a clear-cut. These disturb ed forest sites were adjacent to one another and merged into mature forest. From each forest at least ten individuals of one tree species were sampled using the fogging method. In the primary forest relative proportions of so me arthropod taxa differed on the ordinal and familial level significantly within trees. The dominance of Formicidae was characteristic as was the alm ost complete lack of less mobile arthropods such as Lepidoptera larvae. In the five-year- old forest, differences in relative proportions among most t axa had almost disappeared. Formicidae abundances had declined drastically which coincided with an increase of Lepidoptera larvae. With progressing fo rest succession, arthropod communities increasingly converged on the patter n of primary forest, and total ant abundance as well as diversity increased significantly. Ant communities in the most disturbed forest were of low st ructural complexity, and to a large degree predictable in species arrangeme nt, but became more and more unpredictable as the complexity of the forest increased. Several species of Coleoptera and non-formicine Hymenoptera occu rred in high numbers in the youngest forest, contrasting with the mature fo rest where all species were typically rare. These changes may indicate a ch ange in the structuring mechanisms from predominantly deterministic process es in disturbed forests to stochastic processes in mature forest.