UCLA

The evolution of life on this planet is influenced by many factors, key among them being the means in which predators and their prey interact. Direct morphological evidence for how large mammalian predators evolutionarily respond to their presumed herbivore prey is lacking , but predator richness positively correlates with that of extinct and extant herbivores. In my dissertation, I apply statistical methods to investigate how predators respond to the biodiversity of their presumed herbivore prey over the Cenozoic (66-1Ma).Chapter 1 evaluates the strength of the correlation between North American predators and their presumed prey over the Cenozoic (66-1Ma). I quantify species richness of both the large mammalian predator and herbivore guilds relative to body mass and then apply statistical methods to determine to determine whether the species richness of predators tracks that of their presumed herbivore prey. I observed notable correlations between large (>21kg) wolf-size predators and herbivores of roughly equal size (25kg) and larger. Chapter 2 evaluates whether the predator guild exhibits an evolutionary response to changes in the distribution of herbivore body sizes over the Cenozoic. I quantify species richness of both guilds relative to body mass and then apply statistical methods to determine when either guild underwent statistically significant changes in their distribution of body mass. I then compare these significant shifts to determine if changes in predator guild structure coincide with, or follow, that of the herbivore guild. I observed multiple significant shifts within predator guild that followed shifts in the herbivores and were suggestive of an evolutionary response. Chapter 3 evaluates whether the relative abundance of herbivores, specifically those antelope-size and larger, could be a plausible explanation for species richness trends within the predator guild over the Neogene (23-1Ma). I quantify the occupancy, a proxy of relative abundance, of herbivore genera in relation to body mass and compare that occupancy with predator richness. I observed relatively high (>0.25) and stable occupancy for larger (>25 kg) herbivores despite declining herbivore richness over Neogene , which could explain the unusually high ratio of predator to prey species in the Plio-Pleistocene. Overall, this dissertation demonstrates that body mass, predator diet, and taxonomic diversity influences the evolution of both predator and herbivore guilds and underpins how the former responds to the latter over geologic time.