Coupling Paleoecological Proxies to Infer Competition, Niche Partitioning and Ecosystem Structure in Extinct Mammalian Communities

Abstract

This dissertation explores the paleoecology of mammalian communities in North America at different spatial and temporal scales. Paleoecology uses the fossil record as a tool to develop and test models of species’ response to climate and environmental change. Such models can be critical sources of data when predicting how modern organisms might respond to disturbance resulting from habitat loss due to climate change and other anthropogenic impacts.

Chapter Two examines the dietary ecology of mammoths and mastodons, two proboscideans traditionally considered to have been grazers and browsers, respectively. We use dental microwear and stable isotope data to test for consistency between the two dietary proxies. We demonstrate that the textural properties of foods consumed were highly variable in both taxa, despite stable isotope evidence suggesting rather specialized dietary habits. We show that these strict dietary classification schemes are insufficient for understanding the feeding ecology of such large-bodied proboscidean taxa.

Chapter Three tests for signatures of competition in mammoths and gomphotheres occupying the Atlantic Coastal Plain using dietary proxy data. Results suggest the consumption of similar foods in both taxa and provide evidence for a change in gomphothere diets over time, consistent with expectations of exploitative competition. This suggests that gomphotheres may have been competitively excluded at a time where climate change already bottlenecked resources. This is a critical study in paleoecology, as it is one of the first to provide indirect evidence of competition in extinct megafauna.

Chapter Four reconstructs the ecology of five large mammal taxa from Diamond Valley Lake in California. Using dental microwear and mesowear, we test for changes in feeding ecology before and after the last glacial maximum, and then compare the dietary habits of individuals from Diamond Valley Lake to conspecifics occupying Rancho La Brea. Our results suggest that these species were capable of co-existing over time by specializing on disparate dietary resources. This strategy may have helped to result in one of the largest and most diverse assemblages of megafauna in late Pleistocene North America.

Chapter Five examines patterns in mammal community response to stress over the last 70 million years. We show that the taxonomic magnitude and ecological severity of extinctions are decoupled. Further, intervals of rapid climatic change sometimes led to major losses in evolutionary history, perhaps facilitated by habitat filtering. Our study yields promising results for examining the relationships between extinction trigger, extinction magnitude, and phylogenetic signal in mammalian faunas.