How does conversion from forest to pasture affect the taxonomic and functional structure of the fish assemblages in Amazonian streams?

Abstract

AbstractClearing land for the establishment of pasture is the principal cause of deforestation in the Amazon basin. We investigated how stream habitats and the taxonomic and functional structure of the fish fauna respond to the effects of the conversion of forest to pasture in the eastern Brazilian Amazon. We sampled 13 streams located in areas of forest and 13 streams within a pasture matrix. The structure of the stream habitats, and the taxonomic and functional structure of the fish assemblages were compared between forest and pasture, using univariate and multivariate analyses. Species richness did not vary between environments, although abundance was greater in forest streams. Functional divergence was lower in the pasture streams, indicating a reduced degree of niche differentiation. The pasture streams presented a higher percentage of artificial shelters, such as pipes and plastic containers, and riffles, while the forest streams had greater canopy cover formed by large trees, and a denser substrate formed by leaf litter. Environmental variables influenced the distribution of species based on their functional traits. The greater canopy cover in forest streams benefitted benthic species. The ongoing increase in the area of pasture in the Amazon region is causing changes in stream habitats, and in the taxonomic and functional structure of the local fish assemblages. The impacted streams did not favour the occurrence of species with parental care or piscivorous, invertivorous, and benthic habits. Overall, protecting forests and the stream margins will promote adequate conditions to maintain the equilibrium of Amazonian stream ecosystems.