Processos de montagem e estrutura das comunidades de lagartos da Caatinga

Abstract

In this study, weinvestigate processes determining lizard community structure and assembly in Caatinga environments with different levels of aridity. In the first chapter, we quantified community structure using alpha and beta diversity estimates of taxonomic, functional and phylogenetic data, to incorporate multiple biodiversity dimensions in our ecological models. We used occurrence data of 51 species to quantify lizard alpha and beta diversities is based on phylogenetic and functional data. At the regional scale, we compared communities between the banks of the São Francisco river (SFr) assuming that differences could emerge from regionally interrupted dispersal in at least some of the sampled species. At the local scale, we tested the variation in communities along environmental gradients either directly (temperature, precipitation, relative humidity, drainage density, height above the nearest drainage - HAND) or indirectly (tree cover) related to aridity. At the regional scale, we found that lizard communities were structured by the SFr acting as a barrier to 47% of the species sampled. This finding suggests a riverine barrier as a historical factor structuring communities. At the local scale, communities showed phylogenetic and functional dispersion, although different diversity measures responded differently to different environmental gradients within each of the SFr banks. These findings suggest that lizard diversity in the Brazilian semiarid is limited by competition, which can be enhanced by aridity. In the second chapter, we used the ecological niche theory to test whether four lizard communities partition the use of resources and if such partitioning has ecological or historical basis. We detected nonrandom patterns of niche overlap, specifically higher and lower than expected by chance in the use of microhabitat in Cuité and Casa Nova, respectively. The high niche overlap detected in Cuité suggests intense current competition for available microhabitats or that microhabitats are abundant. The presence of several species with severe adaptations to the sandy habitats of the paleoquaternary dunes of the São Francisco river suggests that the morphology of the lizards is determinant for the partitioning of the spatial niche of the lizards in this location. The random spatial overlap in Contendas do Sincorá and Palmas de Monte Alto indicates that microhabitats are not limiting factor and competition does not play an important role on the spatial niche. We detected trophic niche partitioning of the lizards from Casa Nova, Contendas do Sincorá and Cuité, suggesting thatcompetition in the past was determinant for the assembly of these communities. The random spatial and trophic overlap patterns in Palmas de Monte Alto highlights that competition is not a determining factor for the structure of this community. Phylogenetic effects were predominantly the main determinants for the use of resources in the communities studied.