Patterns of distribution of tree species in the neotropical lowland rainforest biome

This thesis aims to explore distributional patterns of tree species in the neotropical lowland rain forest biome based on diversity analyses, dated phylogenies and species distribution models, using the family Sapotaceae as a case study. Sapotaceae is an abundant and diverse group in the neotropical lowland rain forest and its distributional patterns are representative of other tree clades in this biome. These characteristics make this family a good model to test ecological and biogeographic hypothesis in neotropical rain forests. An analysis of beta-diversity measured by the number of shared species was used as a test of biotic homogeneity of Morrone's (2001) widely used system of neotropical biogeographic units. Biotic homogeneity was generally low, and Morrone's (2001) biogeographic regionalisation was found not to coincide with the distributional patterns of Sapotaceae species. Divergence times of Sapotaceae species were estimated using a dated phylogeny based on DNA sequences of the nuclear ribosomal internal transcribed spacer (ITS) to explore the effects of Andean uplift, closure of the Isthmus of Panama and Pleistocene climatic changes on the evolutionary history of lowland rain forests in northern South America. The Andean uplift was found to have affected patterns of distribution by creating new habitats and altering hydrologic systems in northern South America, and in some cases by isolating lineages to the east and west of the Eastern Cordillera of the Andes. The closure of the Panama Isthmus and Pleistocene climatic changes do not seem to have strongly affected patterns of distribution or diversification in Sapotaceae. In general, the lack of congruent dates for many repeated biogeographic splits in the phylogeny (e.g., Amazon-Choco) suggests that idiosyncratic dispersal events have had a substantial effects on Sapotaceae's biogeography. Finally, species distribution models generated for Sapotaceae in the Neotropics were used to identify areas of high predicted species richness in Colombia. The highest diversity of Sapotaceae species was predicted for the inter-Andean valleys and northern Amazon. These results were compared to the current system of Protected Areas in this country, demonstrating that areas of high conservation value based on predicted species richness have a low coverage of Protected Areas. Such gaps highlight the potential need for new systems for the delimitation of basic units for conservation at national levels in Colombia.