Diversidade de formigas de solo no Cerrado: determinantes hierárquicos entre escalas espaciais

Abstract

To understand why certain regions differ in the number and identity of occurring species is one of the major goals in ecology and biogeography, representing both a theoretical challenge and an urgent conservation need. This thesis aims at studying the patterns of diversity (alpha) and dissimilarity (beta) of ground-dwelling ants in the Cerrado savannas. These patterns were analyzed at different spatial scales, since the assembly of communities depend on ecological and evolutionary factors that operate at hierarchical spatial and temporal scales. In the first chapter of this thesis the species density and diversity (abundance-independent) were calculated at four spatial scales and then modelled by factors related to one of four general hypotheses: i) species-energy; ii) heterogeneity; iii) geographical/historical factors; and iv) local factors. The results show that localities with higher net primary productivity (species-energy hypothesis) are associated to higher diversity of species, since favorable climate lead to lower rates of local extinctions and, thus, more species in the regional banco. On the other hand, the species in the banco are filtered by edaphic characteristics (local factors hypothesis) that control ant abundances. In the second chapter the patterns of compositional dissimilarity (beta diversity) and its components of turnover (species replacement) and nestedness (dissimilarity due to richness differences) were analyzed across five spatial scales that vary in terms of spatial grain (spatial resolution of the sampling unit) and extent (spatial dispersion of samples). The patterns found were then related, in each scale, to five environmental factors: i) species banco sizes; ii) heterogeneity in topography; iii) heterogeneity in the structure of the vegetation; iv) presence of closed habitat vegetation; and v) sand content in the soil. As expected, beta diversity was highest at the smallest spatial scale and decreased with increasing scale, showing a further increase at the largest spatial scale. More species in the regional banco resulted in lower nestedness and higher turnover, the latter being also negatively affected by the amount of sand in the soil. The influence of these factors, however, reduced with increasing scale, being accompanied by an increase in the importance of heterogeneity in vegetation structure. This point to a greater importance of species sorting processes at larger spatial scales. The studies of the present thesis demonstrate the importance of incorporating spatial scale in the analysis of biodiversity patterns, since scale determine the relative importance of the ecological and evolutionary factors that generate these patterns. Understanding how these factors interact is, thus, fundamental to appropriately design conservation strategies that counter the effects of the global biodiversity crisis.