Efeito do gradiente de distúrbio antrópico sobre padrões de diversidade alfa e beta de macroinvertebrados em riachos neotropicais

Abstract

A way to study the spatial distribution of biodiversity in riverine landscapes is to separate it in a local component (alpha diversity), a variation component (beta diversity), and a regional component (gamma diversity). This thesis evaluated the effects of human alterations on alpha and beta diversity patterns of macroinvertebrates in two river basins (High Araguari and High São Francisco river basins) in the Cerrado biome, located upstream hydroelectric reservoirs. We applied the field protocol developed and applied by the Environmental Protection Agency of the United States of America (US-EPA). In the first chapter we developed an integrated disturbance index (IDI) using data from local (in-stream and riparian vegetation) and from catchment scales, analyzing the land uses. This index was used for defining the least- and most-disturbed sites available, necessary for the development of the next chapters. In thesecond chapter we analyzed the efficiency of the fixed-fraction subsampling method characterizing family richness of the site samples (alpha diversity). We verified that, independent of the ecological condition of the sites, higher the number of individuals of the samples smaller the fraction necessary to represent their taxonomic richness. In the third chapter we evaluated which field sampling and laboratory processing methodologies studying macroinvertebrates better differentiated least- and most-disturbed sites according to the assemblage composition and biological metrics. We verified that sampling in many types of habitats (multihabitat sampling) better differentiated the assemblage composition (presence/absence and relative abundance data) and the family richness when counting all individuals of the samples. However, leaf packs (targeted) sampling was more robust when applying fixed-count subsampling of individuals. The fourth chapter evaluated the influence of anthropic alterations on alpha (site) and beta diversities of macroinvertebrates. We verified a negative effect of the intensity of human disturbances (IDI values) on the genera richness of Ephemeroptera, Plecoptera and Trichoptera (EPT) of the sites. It was observed a nestedness pattern along the disturbance gradient; assemblages of the more disturbed sites are subsets of the assemblages of the less disturbed sites. Still, the beta diversity among most-disturbed sites wasgreater than the beta diversity among least-disturbed sites. We conclude that the decrease of the regional richness (gamma diversity) observed in the mostdisturbed sites was caused mainly by local extinctions of species, and not through biological homogenization of the aquatic landscape.