Nascentes tropicais em áreas de silvicultura do eucalipto: estrutura e composição de Ephemeroptera, Plecoptera e Trichoptera (Insecta)

Abstract

Springs are ecosystems of ecological, economic and social importance. However, in view of the expansion of agricultural activities in tropical regions, the pressure on these ecosystems has increased. Despite their importance, tropical springs in areas with different land use are poorly studied. Therefore, this thesis, which is structured in three chapters, aims to broaden the knowledge of the impact of areas cultivated with eucalyptus and rainfall seasonality in Brazilian tropical springs, based on the structure and composition of Ephemeroptera, Plecoptera and Trichoptera assemblages (EPT). In the first chapter, we verified whether the particle size composition of sediment from springs in forest areas differs from springs in areas planted with eucalyptus, since the conversion of natural forests can promote changes in the composition of sediment in aquatic environments. It was possible to observe that springs in forest areas were associated with very coarse sand, while those in eucalyptus areas were associated with finer particle size particles, which emphasizes the importance of riparian vegetation to mitigate potential impacts of eucalyptus forestry on the sediment from the springs. In the second chapter, we use the taxonomic and functional structure of EPT in order to verify the impact of eucalyptus forestry on the environmental quality of neotropical springs. Our results showed that springs in eucalyptus areas showed reduced richness and change in the composition of EPT genera compared to springs in forest areas. We also verified that respiration and body size were the functional traits most influenced by abiotic variables in springs both in eucalyptus and forest areas. The reduction and homogenization of riparian vegetation reduced the quality of the plant substrate, leading to loss of richness and alteration of the functional traits of EPT in springs in eucalyptus areas. In the third chapter, we employ the beta diversity and components, replacement (turnover) and loss of species (nestedness) of EPT assemblages to verify the influence of dry and rainy seasonal periods on the environmental stability of springs in forest areas and eucalyptus areas. The springs showed environmental stability between the dry and rainy periods, with no significant variation in beta diversity in both areas, and due to the heterogeneity of habitats in the springs, species turnover was predominant. We also verified homogeneity of environmental parameters between the dry and rainy periods, and despite the low variation of beta diversity, the fine sand variable, conductivity and turbidity were the best predictors in forest and eucalyptus areas, respectively. We believe that the studies contained in this thesis have contributed to broadening the knowledge of the influence of land use on Brazilian tropical springs, as well as pointing to the need to ensure the preservation of the proportion of riparian vegetation, in order to avoid changes in the natural conditions of the spring ecosystem.