Brazilian ants: the role of ecological factors on their diversity and foraging activity patterns

Abstract

One of the main goals of ecology is to understand the geographical variation in biodiversity. Despite little consensus, many hypotheses have been formulated in order to explain the mechanisms of species richness and ecological niche variation. Moreover, the geographical variation of foraging activity, which is the basis of ecological processes, has been neglected in comparison to other macroecological patterns. Here, I evaluated the role of ecological factors (temperature, precipitation, climatic stability and net primary productivity) on ant biodiversity in six Brazilian biomes. Specifically, I evaluated the effects of ecological factors: (1) on ant species richness and niche overlap, and (2) on ant foraging activity and resource use. (1) For the first aim, in general, I observed that all the evaluated ecological factors positively influenced ant species richness. However, the majority of the explained variance was due to precipitation, followed by climatic stability. These ecological factors also positively influenced local species richness; however I found no indirect effects of them on local species richness mediated by niche overlap. Nevertheless, precipitation negatively and directly influenced ant niche overlap. I suggest that in warm and productive regions, such as Brazilian biomes, high species richness and ecological niche diversity could be explained by greater time for speciation and to lower extinctions rates that occur in wet and more climatically stable regions. Thus, I suggest that ant diversity could reflect the evolutionary history of the biodiversity in Neotropics. (2) For the second aim, I also found a positive influence of all ecological factors on ant foraging activity. However, these patterns seem to be confounded with species richness. Ecological factors also influenced ant resource use in a complex way. Temperature and precipitation can be linked to an improved performance in ant foraging activity, and climatic stability and productivity can be linked to an increase in ant abundance in these regions, which increases the probability of finding resources. Ecological factors also influenced the selection for particular resources, which could be due to their role in resource shortfall in the environment and to their action on resource demand by organisms. In this sense, this thesis advances the understanding of ecological theory because, besides demonstrating the possible mechanisms of the geographical variation in ant diversity, these findings may be useful for guiding the conservation of Brazilian biodiversity. According to my results, I also suggest that some niche aspects could be conserved in evolutionary time, for example, humidity demand could reflect current ant species richness and how much and how ants forage. Consequently, rapid environmental changes, such as by climate change and deforestation, could drastically affect ants, that in their turn, may not be able to adapt to such fast changes.