Diversidade funcional: como incluir a variação intraespecífica e o efeito do fogo em comunidades vegetais do cerrado
Cianciaruso, Marcus Vinicius
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Biological diversity may influence the structure and functioning of communities in several ways, for example, altering the species resource complementarity. However, traditional diversity measures (such as species richness or diversity indices as Shannon or Simpson) have being considered as rough biodiversity estimators. In that sense, several authors suggest that measures taking in account phylogenetic or functional relationships among species would be better predictors than those traditional measures. We can split this thesis in three fractions relatively distinct. The first, compounded by the first chapter, is a brief review on the properties of two promising approaches in Ecology measures of phylogenetic diversity and functional diversity. We present and discuss briefly the major concepts, approaches and applications of these measures that are relatively new to Community Ecology. Podemos divir esta tese em três partes relativamente distintas. The second part, represented by the second chapter, is more theoretical and suggests a simple manner to incorporate the intraspecific variability in functional traits in a functional diversity measure. In this chapter, we demonstrate throught simulations and using empirical data, that it is possible to include the functional variability existing within local populations, and also the variability that exists among populations occurring in disticnt geographical areas. The third section is compoused by the third and fourth chapters where we investigated the effects of different fire frequencies in the structure of cerrado communities. How does fire structures the cerrado woody species in terms of their relatedness and functional traits? In the third chapter we analised the phylogenetic and functional diversities of the cerrado woody species under annual fires, biannual fires, and under fire exclusion for 12 years. We discuss the consequences of an increasing in fire frequency upon these diversities, and also which is the contribution of rare species to those measures. We found that under annual fires functional diversity is reduced significantly, that is, fire selects similar individuals in their functional traits when compared to communities under biannual or fire exclusion. Therefore, high frequency fire is an environmental filter selecting functionally similar species. Also, we show that rare species are important to this diversity. However, we did not find any difference for phylogenetic diversity, that is, different fire frequencies do not change species relatedness in average. Therefore, functional diversity might be somehow independent from evolutionary history. In the fourth chapter we studied the herbaceous-undershrubby species. We investigated the effects of different fire frequencies in total above-ground biomass and also the biomass of functional groups (the tussock grass Tristachya leiostachya Nees, other grasses, woody species, and dry biomass) in savannas subjected to annual fires, biennial fires, and protected from fire in a 12 yr period. Protection from fire during 12 yr resulted in the accumulation of total biomass, which was more than twofold higher in the protected site than in the annually burned site. The negative correlation of T. leiostachya with other grasses and woody species in the annually burned site supports the idea that frequent fires favor this species, and may indicate an outcompeting effect. Therefore, knowledge not only about biomass but especially about its functional components is important to provide a better understanding of the processes and consequences involving different burning strategies.