Date of Graduation
Master of Science in Biology
College of Arts and Sciences
John R. Paul
Why do some species have broad geographic distributions, while other species are confined to a narrow distribution? Species age, ecological niche, or dispersal traits may help explain why some insular species are abundant and found on many islands, while others are rare and restricted to one island. In this study, I inferred a robust, time-calibrated phylogeny of the Hawaiian Psychotria, using two nuclear and eight chloroplast loci, sampling 67 individuals. I coupled my phylogenetic hypothesis with climatic data, ecological niche modeling, and morphological dispersal characteristics to explain the variation in number of islands occupied by each species. My inferred phylogeny showed stronger support for many relationships among the Hawaiian species. Restricted lineages on the older islands were found to be basal, while younger, derived species were more widespread. The species that have managed to disperse to and colonize multiple islands are the younger species. The biogeographical South Pacific Psychotria suggests strong biogeographic structure, with early divergences of major clades and very few species subsequently dispersing and colonizing other geographic regions. Results of niche breadth and climatic niche models of the Hawaiian species indicate a general pattern of older species having narrower climatic niche breadths, which may explain their smaller geographic ranges. In contrast, the younger species have wider climatic niche breadths, which may explain why they occupy larger geographic ranges across multiple islands. However, multiple regression analysis indicates greater plant height (associated with dispersal abilities) has the strongest weight in explaining the number of islands Hawaiian Psychotria species occupy.
Zhang, Elaine, "Phylogenetics, biogeography, and climate niche variation of South Pacific and Hawaiian Psychotria" (2016). Master's Theses. 222.