Doctor of Philosophy (PhD)


Biological Sciences

Document Type



The origin and maintenance of biological diversity has been one of the fundamental issues in biology. However, the evolution of ecological traits that affect species coexistence and species diversity is poorly known. My research aimed to investigate the evolution of species-specific ecological and morphological traits and to understand the process of ecological diversification and species coexistence in Tangara tanagers (Thraupidae) by using phylogenetic comparative methods. Tangara is the largest avian genus in the New World with 50 recognized species. As many as ten species of Tangara are found sympatrically in the same Andean cloud forest, and many syntopic species travel together in mixed-species flocks. The distribution of Tangara covers all of subtropical and tropical America from sea level to tree line; thus, Tangara species show a wide range of habitat preferences as well as strong variation in number of coexisting species and species combinations. Like many other species of tanagers, Tangara species are omnivorous; their diet consists of both insects and fruit. I collected extensive ecological and behavioral data at six study sites to quantify ecological differences among sympatric species. I measured museum skins and skeletons to define morphospace of each taxon. DNA sequences were used to build a molecular phylogeny, which reveals the speciation pattern. I combined ecological data, morphological data, distributional data from literature, and a molecular phylogeny by two phylogenetic analytical methods to elucidate evolution of ecological diversity among 25 Tangara taxa. Permutational phylogenetic regression analyses showed significant phylogenetic effects for arthropod foraging, but not for fruit foraging, habitat use, and elevational distribution. A disparity-through-time plot showed that the relative disparity of arthropod foraging decreased more rapidly than the other niche axes. These analyses revealed diverse evolutionary patterns unique to each niche axis. The relative strength of phylogenetic effects, frequency of homoplasy, mode of evolution, and association with morphology differed substantially among the four niche axes. Fruit foraging and habitat specialization showed the greatest ecological plasticity in relation to phylogeny, and the variation in microhabitat preference in arthropod foraging associated with species-specific attack maneuver was the most conservative and consistent with the phylogeny.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

J. V. Remsen, Jr.