Importância relativa da seleção natural e deriva ecológica nos padrões de riqueza e abundância em comunidades de ácaros Oribatídeos em uma floresta ombrófila densa na Amazônia

Abstract

Four ecological processes can summarize the various mechanisms that shape species richness and abundance within communities: natural selection, ecological drift, dispersion, and speciation, but little is known about the contribution of each of these processes to patterns of diversity. This study aimed to investigate the relative importance of selection and drift processes in relation to the effects of five environmental variables on the abundance and richness of oribatid species. We used data from oribatid mites sampled from March 18th to May 13th, 2002, in 55 plots along a Dense Ombrophilous Forest landscape. We also used data from five potentially influential variables on the oribatid community (soil clay content, soil phosphorus content, soil moisture, litter average dry weight, and tree species richness). Multiple regression analyzes were performed to 1) evaluate the relationship of environmental variables on the abundance of oribatid mites and 2) on oribatid mites richness but including oribatid mites abundance as a predictor. Clay percentage, soil phosphorus content, soil moisture influenced the abundance of oribatid mites. There was a positive relationship between oribatid mites abundance and clay percentage and phosphorus content predictors and a negative relationship with moisture. None of the environmental variables influenced the richness of oribatids. However, oribatid mites abundance had a strong influence on the species. The results suggest that ecological drift is the main process directly influencing the richness of oribatid mites through variations in the number of individuals within the community. We suppose that oribatid mite species are ecologically equivalent, responding similarly to environmental gradients at the level of landscape.