Padrões e processos ecológicos relacionados à montagem de comunidades no semiárido tropical brasileiro

Abstract

Community ecology studies patterns of diversity and processes underlying those patterns. Many studies only consider taxonomic diversity (TD), but the evolutionary history (phylogenetic diversity, PD) and functional traits (functional diversity, FD) of species can also be used to understand the processes that structure diversity patterns, especially taking into account the alpha and beta components of diversity. The use of these approaches allows a better understanding of the relationships between species and the environment since the functional traits of the species can be the result of both the relationship and the species' responses to the environment. Thus, this thesis had the following objectives: (i) test if the variations of the functional traits in the tropical semiarid are responses of the abiotic variables, evolutionary history or by stochastic events and (ii) analyze the congruence between TD, PD and FD different conditions of water and soil availability. In order to answer these objectives, the climatic variables were estimated, the chemical and physical variables of the soil were determined and eight functional traits were measured in 20 areas distributed in a precipitation gradient (502 to 1,423 mmyear-¹) in the semiarid region of northeastern Brazil. Considering aim (i) it was found that there is no influence of the evolutionary history on the variation of the functional traits and that the climatic and soil factors influenced a combination of functional traits that allowed to identify two trade-offs one between leaf area and basic density of branch wood and other leaf area and height. Considering the objective (ii) the three facets of diversity showed different patterns of change in the tropical semiarid. In the alpha component, there was congruence between the different facets of diversity. However, in the beta component in the drier areas, they showed a decrease in taxonomic and functional diversity and an increase in phylogenetic diversity, indicating a pattern of mismatch between these facets of diversity. Different ecological processes drove the communities’ assembly of in the northeastern semiarid, since there were contributions from processes related to the niche and stochastic events. Thus, it is concluded that the variations of the functional traits were responses to the variations of the environment and not to the evolutionary history and that the patterns of assembly of communities in the semiarid differ in the aspects of diversity. The study pointed out that the processes that act to promote the assembly of communities in the tropical semiarid vary with water availability.