DISSERTATION RESEARCH: Diversification in Trees of the Lowland Neotropical Rainforest, Based on Studies of the Ubiquitous Legume Swartzia

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A grant has been awarded to Dr. Barbara Schaal and Mr. Benjamin Torke at Washington University to study species origins and evolutionary relationships in Swartzia, a diverse genus of tropical trees that occur in lowland rainforests of Central and South America. In terms of structure, productivity, and botanical species richness, lowland rainforests are dominated by trees, but the evolutionary mechanisms that underlie diversification (i.e., genetic and morphological divergence and species origination) in tropical trees are largely unknown. Hypotheses range from those that postulate high rates of species origination driven by historical climate and landscape changes to those that stress the role of modern transitional habitats. This study will test contrasting diversification hypotheses by identifying statistical correlations between the locations of geographical features, such as transitional habitats, and spatial patterns of genetic and morphological variation within and between species of Swartzia. A significant portion of the field and laboratory work will be carried out in Eastern Brazil in close collaboration with Dr. Andre Amorim of the Universidade Estadual de Santa Cruz-Bahia, Brazil. Human mediated destruction of tropical rainforests and associated loss of biodiversity is a problem of international concern. Approximately half of all species on earth occur in tropical rainforests. Many hold great potential as sources of food, medicine, and building material. Effective conservation of rainforests will require detailed knowledge of the processes that generate and maintain biodiversity. Despite the fundamental role of trees in these ecosystems as the dominant botanical component, diversification has been poorly studied in tropical trees. Are historical mechanisms sufficient to explain species diversity or do modern habitat heterogeneity and transitional habitats effectively maintain genetic and morphological divergences between species? By making significant contributions toward answering these questions, this study will have important implications for prioritizing conservation in lowland rainforest areas to maximize protection of biodiversity