Diversidade e biogeografia de aranhas do Brasil: esforço amostral, riqueza potencial e áreas de endemismo

Abstract

The reduction of Earths biodiversity through an unprecedently high extinction rate is one of the biggest environmental problems of the twenty-first century. In addition, the knowledge about biodiversity remains incomplete, particularly in the tropics, where there is still a large number of species to be described and very little is known about its distribution. The knowledge of geographic distribution of organisms and the processes involved in these patterns is fundamental for conservation practices. The current rate of biodiversity loss demands an efficient compilation of data currently available for studies of biogeography. These studies are crucial for directing collection efforts, and to establish priorities for conservation. In this sense, species distribution databases may be useful not only to understand the current state of knowledge about the diversity and distribution of several taxa, but also as a source of data for biogeographic analyses. In this dissertation, a database of spider species distribution is used as a model for studies on biogeography of the Brazilian biomes. This study is organized in three chapters. Chapter I focuses on the quantification of the influence of sampling bias on the perception of spider species richness in Brazil, and proposes an alternative approach to identify areas of high diversity, regardless of those bias. Chapter II tests the influence of inequalities in sampling effort on species richness estimators and on a model of species richness based on environmental modeling. The results of this analysis are used to propose a map of priority areas for inventory, based on the geographic variation of species richness predicted by the model and the known sampling effort. Finally, Chapter III has two main goals: (1) to propose a new method for identifying areas of endemism by means of distributional overlap of narrowly distributed species, using a kernel density interpolation method. (2) To test the hypothesis that environmental factors can act as barriers to species distribution and thereby determine the limits of areas of endemism. It is also tested whether historical climate factors, such as the Pleistocene fluctuations, are related to the separation of areas of endemism.