Trophic Structure Evolution in Oregon Oligo-Miocene Terrestrial Communities

The goal of my dissertation is to expand our knowledge of how mammalian diets are affected by and affect other ecological and evolutionary processes. I did this by evaluating how diet is related to mammalian diversity, body mass, and evolution. I also evaluated and how environmental change affects mammalian functional diversity and community structure. I first, investigated whether tooth-size variation is driven by functional demands. I found that tooth-size variation is not determined by developmental controls or functional demands alone, but a combination of factors influence carnivoran tooth-size variation, such as differences in ontogeny, diet, sexual dimorphism, and evolutionary history. Next, I evaluated how type of omnivory is related to mammalian diversity, body mass, and evolution. Complete generalists are rare and most omnivorous mammals consume only invertebrate prey and non-fibrous plants. Omnivores that only consume invertebrate prey are on average smaller than omnivores that incorporate vertebrate prey. Transition rate models show that there are high transition rates from insectivorous omnivory to herbivory, and from vertebrate predation to prey mixing and ultimately insectivory. This work highlights that prey type is an important aspect of omnivore macroevolution and macroecology, as it is correlated with body mass and diet-related evolutionary transition rates. Next, I evaluated how past environmental change affected mammalian functional diversity and community structure in Oregon. Using the combined functional diversity and food web results, my work emphasizes that as the landscape changes, certain mammalian functional groups are lost. I show that these extinct communities are characterized by a decline in browsing species and mid-sized omnivores being replaced by more specialized hypercarnivores. Finally, using stable carbon isotope values I found that Oligo-Miocene ungulates were partitioning C3 plant-food resources. My work shows that a more homogeneous ungulate community arose as global temperatures decreased, and grasslands expanded