The processes regulating biodiversity (numbers of species that exist at a particular place) on islands are conventionally thought to be colonization from other areas and extinction within an island. Large islands, however, may contain many species whose closest relatives occur only on the same island, indicating within-island speciation. Within-island speciation may result from geographic environmental fragmentation events and spatial heterogeneity of habitat types. This dissertation examines the roles of these two factors in the evolutionary diversification of ground-dwelling lizards on Hispaniola. Molecular-genetic data are used to examine the genetic relationships within and among five species of Leiocephalus and three species of Ameiva. Species- and population-level phylogenies are examined in the context of environmental data using Geographical Information Systems technology to test the hypothesis that environmental variation plays a significant role in species formation among ground-dwelling lizards. Geological information is used to test the role of historical environmental fragmentation in lizard diversification. Local environmental variation is used to examine geographic variation in morphological characteristics thought to have adaptive significance.
This study explicitly identifies environmental and population-genetic conditions that promote and maintain an evolutionarily diverse island fauna. The study integrates data from diverse sources to test hypotheses about the diversification of an understudied fauna. This study also benefits local students by fostering international collaborations in the Dominican Republic and enhancing understanding of evolutionary and conservation biology.
