Publication Date


Document Type


Committee Members

Volker Bahn (Advisor), Steve Matthews (Committee Member), Thomas Rooney (Committee Member), Thaddeus Tarpey (Committee Member), Yvonne Vadeboncoeur (Committee Member)

Degree Name

Doctor of Philosophy (PhD)


The unifying themes of my thesis are patterns in world-wide freshwater fish body sizes and their underlying mechanisms. First, I explored Bergmann's rule in unprecedented detail, which states that body size is negatively correlated to temperature. Categorizing species by body size into quantiles and by trophic levels, I regressed the classes against latitude, temperature, seasonality, minimum temperature and habitable space. I found that Bergmann's rule applies to freshwater fish in general but the strength varies by size class and trophic levels. I concluded that Bergmann's rule in fish is driven by the exclusion of small fish from cold climate due to limits in energy storage and behavioral thermoregulation. Second, I investigated the relationships between extreme body size and species richness. Stressful environments promote an ecological similarity among species, reducing body size ranges and species richness. Thus, there may be a strong relationship between extreme body size and species richness. However, I found that only the size of the smallest species were strongly related to species richness. The observed strong relationship may be due to physiological constraints on the smallest species in stressful environments. The lack of relationship between the size of the largest species and species richness may be due to the high dispersal ability of the largest species homogenizing body size across space and their relative insensitivity to harsh environments. Third, I examined body size and trophic level conservatism and similarity across species within a genus. Body size and trophic level are evolutionary conserved traits; thus I expected high body size conservatism, but due to constraints imposed on extreme body sizes and trophic levels, body size conservatism may vary for all body size classes and trophic levels. I found conservatism of these traits to be substantially lower in freshwater fish than mammals. Divergence in body size among closely related species that are very small or large may allow those species to reduce constraints due to extreme size and to coexist with other species, leading to lower body size conservatism than in the medium size class. Relatively low body size conservatism and high similarity in body size among families and genera, suggest that freshwater fish body sizes are, in contrast to mammals, highly plastic and responsive to environmental variations. Trophic levels were more conserved than body size. Trophic adaptation connects species by their function and physiology. In addition, it also demonstrates the direct interaction between species and their community and ecosystem processes.

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Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded


Creative Commons License

Creative Commons Attribution-Noncommercial-Share Alike 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.