Atributos funcionais vegetativos e fatores ambientais em savanas sul-americanas: legados históricos da megafauna extinta e pressões atuais de clima, solo e fogo

Abstract

South American savannas represent one of the most biodiverse ecosystems on the planet, resulting from the interaction of historical, environmental, and functional factors. Traditionally, their origin and maintenance have been attributed to poor soils, seasonal climate, and recurrent fire regimes, but recent evidence points out to a potential role of extinct megafauna in shaping some South American savannas. In this thesis, I aimed to integrate evolutionary legacies and current environmental pressures to understand the functional ecology of Neotropical savannas. In the first chapter, we investigated the legacy of extinct megafauna in Amazonian savannas and the Cerrado by comparing functional traits associated with defense against herbivory, such as wood density, leaf size, spines, and extrafloral nectaries. We observed that Amazonian savannas contain species with higher wood density and a greater proportion of spines, while no significant differences were detected in leaf size or the presence of extrafloral nectaries, supporting the hypothesis that large herbivores played a relevant role in structuring Amazonian savannas during the Pleistocene, leaving functional legacies that distinguish these areas from the Cerrado, where fire appears to have been the main selective force. In the second chapter, we evaluated how present environmental conditions (soil, climate, flooding, rockiness, and fire) influence functional trait variation in South American savannas, evaluating six vegetative traits (leaf area, wood density, bark thickness, height, spines, and latex) and seven types of savannas. This analysis revealed three main groups of physiognomies: (i) Cerrado, Guiana savannas, and Alter do Chão savannas, characterized by thick bark and low investment in height, in cooler climates and dystrophic soils; (ii) rocky and white-sand savannas, with thin bark and higher investment in height, associated with humid climates and acidic soils; and (iii) hyperseasonal and swampy Amazonian savannas, with intermediate bark, low height growth, and low wood density, occurring in warm, humid climates and acidic, waterlogged soils; the presence of spines and latex did not vary significantly among the physiognomies. Overall, the results show that the functional diversity of South American savannas reflects both historical legacies and current environmental pressures; while the legacy of megafauna may have left traces in the defensive traits of Amazonian savannas, variations in climate, soil, and fire continue to shape distinct ecological strategies across different formations.