Distribuição espacial e fidelidade quantitativa de associações vivas x mortas de moluscos da bacia do rio Ibicuí, Brasil

Abstract

The lack of long-term data on communities of mollusks which today occupy impacted rivers and streams may hinder the determination of the degree to that the same are altered. In this sense, quantitative studies on the paleodiversity and spatial distribution of their communities are an important contribution to the knowledge of the biodiversity of freshwater mollusks and preserving the integrity of rivers in southern Brazil. The additive partitioning of species diversity is an efficient method to analyze the species diversity at several spatial scales and identify the most important source and target of efforts to conservation diversity. Another type of study is the quantitative fidelity. This type of analysis aims to assess the degree to which dead assemblages reflect the communities living, and enables answering questions about productivity, biomass and community structure of ancient as well as anthropogenic changes. This study aimed to identify and understand the spatial distribution of communities living mollusks and quantitative fidelity of live and dead assemblages in the Ibicuí River basin, Rio Grande do Sul, Brazil. In chapter one, aimed to assess the distribution of mollusks communities in the Toropi River and partition of community diversity at different spatial scales. The results showed that all species mollusks found, as well as the community overall, exhibited clumped distribution, influencing the partition of beta diversity of communities of freshwater mollusks studied. Chapter two aimed to evaluate the degree of quantitative fidelity of dead and live assemblages mollusks of the Ibicuí River basin, southern Brazil, under the influence of three environmental factors at large and local spatial scale: relief (plain x slope), order of the rivers (small x medium-large) and grain size (gravelly x sandy). The results showed a difference in fidelity between the live and assemblages in the Ibicuí River basin in relation to species composition, dominance and richness. The live assemblages were related to these factors. The species composition of dead assemblages can be used to infer the order of rivers, can be used to reconstruct the order of hydrological environments where they are accumulated. However, the dead assemblies can not be used to provide information about relief because the accumulation of shells are not influenced by such environmental variable.