Influência de fatores ambientais de ampla escala na distribuição espacial de moluscos límnicos

Abstract

This dissertation presents unique approaches about the influence of environmental variables at different spatial scales (meso and macro regional temperature, rainfall and altitude) (1), and aquatic and terrestrial factors on a large scale (2) on the spatial distribution of Brazilian freshwater malacofauna. The study was conducted through meta-analysis, based on distribution data of gastropods and bivalves communities from the existing literature. According to the taxonomic composition, 35 localities from 33 previous studies were selected under certain criteria to minimize specifically sampling deviations. As some studies had focused exclusively on one mollusk class, from all the localities, 27 were used for gastropods communities analysis and 22 for bivalves. Environmental information was obtained from geospatial data. The similarity between gastropods and bivalves communities was represented by a Cluster analysis (WPGMA) and possible graphic distortions were evaluated by Coefficient of Cophenetic Correlation (r). Through a Mantel test, spatial autocorrelation was observed for both communities (r = 0.21, P = 0.02 for gastropods, and r = 0.425, P = 0.0002 for bivalves). Thus, a partial Mantel test was used, comparing the similarity matrixes and the environmental ones removing the geographic distance effect. The Bonferroni s correction was considered due to possible biases arising from sample variability. The dendrogram demonstrated the formation of 4 and 6 small groups, of bivalves and gastropods, respectively, with similarity greater than 50%. The Köppen s climate region had a significant positive correlation with both communities in both approaches (1) (2) despite the space issue. Environmental variables in macro scale (Köppen s climate region and rainfall range) were important in the distribution of gastropods and bivalves. At meso-scale, only altitude had a strong relationship with the bivalves communities. However, despite the obvious influence of the space, terrestrial variables (Köppen s climate region, biome and vegetal formation) had a stronger correlation with the bivalves communities than aquatic ones (hydrographic region and aquatic ecosystem). In addition, the aquatic ecosystem (e.g., lake, river), in this case, was not affected by space. For gastropods communities, in addition to strong correlation with Köppen s climate region, there was some relationship with hydrographic region, but this vanished when the effect of distance was removed. The results of this study indicate that the development of protection strategies for the freshwater malacofauna should consider macrovariables as Köppen s climate region, biome and even altitude, and the integrity of limnic ecosystems should also be included in conservation programs.