Document Type



Master of Science



Date of Defense


Graduate Advisor

Nathan Muchhala


Sebastian Tello


Fredrik Inglis


The high species richness that angiosperm show has been extensively correlated with key floral innovations. Key floral traits contribute to species boundaries and the origin of new species. However, how these relate to extinction remains largely untested. Among the multiple theories that attribute diversification to floral innovations, the reduced extinction model predicts that floral specialization allows the persistence of small populations and avoids their loss. Bilateral symmetry (zygomorphy) is a trait that has evolved recurrently in angiosperms. It is a form of floral specialization that restricts pollination to fewer visitors and precisely places pollen to ensure more effective transmission of pollen between conspecific flowers. In this study, I investigate the relationship between floral symmetry and abundance of species from 33 (1 ha) plots in tropical and subtropical forest in the Madidi National Park, Bolivia. If zygomorphy reduces the extinction of rare species, that is, species with small local abundance and low occupancy then, zygomorphy is present in smaller and more dispersed populations. For this, I carry out linear models with phylogenetic correction that explain the abundance of 545 species according to zygomorphy of the petals, of the stamens and stigma, and corolla shape. Results show that corolla zygomorphy is present in species with smaller populations. Species that contribute to this pattern are mainly present in the species-rich sub-humid and humid forest. However, zygomorphy of the reproductive organs does not have a significant impact in species abundances except for the analysis of species from the higher elevation. Multiple selective forces can shape the abundance of species. When facing the biotic forces that affect success of reproduction, such as pollinator availability and interspecific pollination, zygomorphy seems to provide an advantage to species that are rare by allowing them to persist at low abundances. More studies that further explore the causes for zygomorphy in smaller populations and the extinction rate using phylogenetic methods can help to understand how species loss is avoided.