Efeito da distância geográfica e das variáveis aquáticas sobre a comunidade de Odonata (ninfas) de lagos na savana de Roraima, Brasil

Abstract

Despite growing efforts to determine Brazilian biodiversity there is still a gap in knowledge about aquatic insects, it is not a taxonomy and ecology, especially in the natural lakes of the savanna of the state of Roraima, because of its location in the extreme north of the country, where few researchers They act. To evaluate how a community and structure in the environment is important, consider the effect and the environment and a geographic distance on it, because a distribution of species depends on the condition of the environment and the dispersal power of the species. Adults Odonata (Insecta) has been a good model in attempting to understand these effects. However, evaluating the community using the nymphs rather than the adults, ensures that the species collected actually belong to the sampled site and not just visitors, as can occur with adults. To characterize Odonata fauna (composition, richness and abundance) and to verify the influence of the geographic distance and the environmental characterization of the savanna lakes of Roraima on the community of Odonata, we conducted a study in 25 lakes in the municipalities of Alto Alegre and Boa Vista, In August 2015 (beginning of the rainy season in the region). In each sampled lake, besides the fauna of Odonata collected with rapiché, were measured: geographic coordinates and environmental variables of the water (oxygen, pH, temperature, electrical conductivity and phosphate). In each sampled lake, besides the fauna of Odonata collected with rapiché, were measured: geographic coordinates and environmental variables of the water (oxygen, pH, temperature, electrical conductivity and phosphate). The following hypotheses were tested: i) environmental since Anisoptera has species considered good dispersers, only environmental variables should have an effect on their composition; Ii) because Zygoptera has species with lower dispersion capacity and more sensitive to environmental variations, both environmental and spatial variables should have an effect on the composition of Zygoptera. To represent the abundance of Odonata, Anisoptera and Zygoptera species in the Partial Redundancy Analysis (pRDA) and in the multiple regressions the first axis of the Principal Coordinates Analysis was used (PCoA). In order to evaluate the spatial influence the geographical coordinates of the lakes were used to obtain a matrix of Euclidean distances, a Principal Coordinates Analysis of Neighboring Matrices (PCNM) was made and the obtained axis was used as spatial variable in the pRDA. In addition, to determine the importance of environmental variables on the communities, multiple regressions were performed with the abundance, richness and composition of Odonata, Anisoptera and Zygoptera. In all, 12,462 nymphs were collected in 20 species (12 of Anisoptera and eight of Zygoptera). The geographical distance between lakes did not have an effect on the structure of Odonata, Anisoptera and Zygoptera, while the environment had an effect on the composition of Anisoptera and Zygoptera. Dissolved oxygen exerted a negative influence on Odonata abundance, while pH positively influenced the abundance of Odonata, Anisoptera and Zygoptera. Phosphate positively influenced only the abundance of Anisoptera species. No environmental factors influenced the richness of Odonata species and both suborders. For the composition of the species, the temperature was important for Odonata, while the conductivity had an effect on Odonata and the suborder Anisoptera. It was not possible to verify the influence of the geographical distances between lakes on the abundance, richness and / or composition of species. Therefore, in order to understand local diversity and plan maintenance and preservation of the environment and fauna, it is important to verify the contribution of organic matter, pesticides, fertilizers and urban waste in these natural savanna lakes of Roraima.