Comunidade de invertebrados aquáticos como ferramenta para avaliar o efeito do uso da terra sobre riachos da Amazônia Oriental, Brasil /

Abstract

Land use is the main threat to biodiversity and natural ecosystems, especially in the tropics, where original vegetation has been replaced by agricultural crops to meet global demand for food. Understanding ecosystem dynamics in landscapes dominated by agriculture is critical to implementation of conservation measures. The aim of the present thesis was to evaluate effects of land use on low-order streams in the eastern Amazon using variations in taxonomic and functional structure of aquatic invertebrate communities. For better understanding, this thesis was divided into three chapters. The first chapter evaluated the existence of a change point in the invertebrate community in relation to vegetation cover loss. Threshold indicator taxa analysis (TITAN) results indicated existence of a change point for the most sensitive taxa at 4.4 and 5.9% of vegetation cover loss. This sharp decline of sensitive taxa in response to a small loss of vegetation in a 30 m wide buffer on each stream bank is a strong indication that the required “Permanent Preservation Area” is insufficient to protect stream invertebrates and possibly other organisms in Amazon rainforest areas. In the second chapter, congruence between the aquatic invertebrate community and three subgroups of the community: (EPT [Ephemeroptera, Plecoptera and Trichoptera], Odonata and Trichoptera) and within the community at the genus and family levels were assessed using Procustes analysis. High congruence was recorded between community and EPT (94% and 96%) and between community and Trichoptera (73% and 84%). Odonata presented moderate congruence with community (68%). The two taxonomic resolutions also showed strong correlation (85% and 91%). Due to cost-benefit it is suggested that Trichoptera (abundance) or invertebrates at the family level be used as substitutes for the invertebrate community in assessments and in conservation of streams under the influence of agriculture. The third chapter evaluated effects of land use/ cover and natural habitat metrics on diversity and functional structure of the EPT community in lower order streams of the eastern Amazon. Increase in anthropogenic disturbance reduces EPT richness and functional diversity in Paragominas and Santarém. Community structure has also changed with intensification of anthropic disturbance, especially in Paragominas, where vegetation loss in the riparian zone was higher. These results show that species loss affects aquatic community functionality, and this should reflect on stream functioning. Finally, it was possible identify the effects of land use (agriculture) on the low-order streams in the eastern Amazon using variations in the taxonomic and functional structure of aquatic invertebrates community