Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Ecology, Evolution, and Organismal Biology


Ecology and Evolutionary Biology

First Advisor

Dean C. Adams



For centuries, biologists have asked "why are there so many species, and why do we see such magnificent biological diversity?" This dissertation addresses this question by examining sexual size and shape dimorphism hummingbird bills at both a micro and macroevolutionary scale. Specifically, I quantify sexual size and shape dimorphism of bill morphology of 269 species of hummingbirds and begin with a species-level study to find that community structure might be a driving factor in the evolution of sexual size dimorphism in 2 sister species of hummingbirds, and the presence of sexual shape dimorphism in one of those species.

I then broaden my study to a clade-level analysis, examining the Mellisugini clade. I find that, while the majority of hummingbird species in the clade exhibit sexual size dimorphism, only 3 of 32 display shape dimorphism. Exploration of factors that may be underlying these patterns may be community structure, where species-poor communities tend to have a greater degree of sexual dimorphism than those in species-rich communities.

I scale up once more in a final study at the family level to investigate patterns of size and shape dimorphism in bill morphology. I find that there was no significant correlation between the mean magnitude of size dimorphism and the magnitude of shape dimorphism and that the rates of evolution of sexual size dimorphism did not predict those of shape dimorphism. This suggests that these traits are evolutionarily decoupled. I also found that the rate of sexual shape dimorphism, species richness, and rate of species diversification are all positively correlated, implying that these are predictors of species richness. These relationships are consistent with the macroevolutionary theory of `punctuated equilibrium', but also may result from the opening of new niches and the presence of `adaptive zones'. In combination, I demonstrate that microevolution alone cannot explain macroevolution, but requires the integration of processes at multiple hierarchical scales and in this dissertation, I elucidate a rich picture of the evolution of diversity.

Copyright Owner

Chelsea Marie Berns



File Format


File Size

188 pages