Biotic and Abiotic Factors Influencing Diversification of Herbivorous Mammals.

Abstract

Though biotic and abiotic factors controlling diversification are believed to operate at distinct temporal and spatial scales, in reality the scales at which key processes of diversification operate often are ambiguous or unknown. To explore the spatiotemporal dependence of diversification factors, my dissertation examined the interaction between lineage-specific traits and ecology as well as environment at multiple taxonomic, temporal, and spatial scales. I focused on the effects of a novel digestive strategy, foregut fermentation, in the herbivorous mammals. In Chapter II, I tested predictions of a popular macroevolutionary model to evaluate the role of an abiotic factor, ecological opportunity, in the diversification of the foregut-fermenting colobine monkeys. In addition to the abiotic factor, I also found evidence for an important role of dietary specialization, a biotic factor, in the diversification of Asian colobines. These findings showed that both biotic and abiotic factors can be important controls on diversification at long timescales and large geographical scales. In Chapter III, I tested the effects of foregut fermentation on the relationship between ecological specialization and speciation rates in the terrestrial, herbivorous mammals. My findings indicated that foregut fermentation mediated speciation rates in mammals, supporting roles for both biotic and abiotic factors in determining differences in speciation among clades at intermediate temporal and geographical scales. In Chapter IV, I investigated the effects of environmental change, specifically historical climatic perturbations, and its interaction with digestive strategy on speciation rates of the terrestrial, herbivorous mammals. I found that climatic instability since the Last Glacial Maximum had stronger, multifarious effects on the richness of foregut-fermenting mammals. In contrast, hindgut herbivores experienced bounded instability across the continents on which they occur. These findings support important roles for both biotic and abiotic factors on species richness over short timescales and intermediate geographical scales. Overall, my findings from Chapters II-IV together show that not only are the effects of biotic and abiotic factors on diversity important on spatiotemporal scales not currently recognized in the multilevel mixed model, but the effects of the factors themselves are likely to vary based on the biological and ecological differences found within and among clades.