Variations in insect herbivory on angiosperm leaves through the late Paleocene and early Eocene in the Bighorn Basin, Wyoming, USA

Climate, terrestrial biodiversity, and distributions of organisms all underwent significant changes across the Paleocene-Eocene boundary (55.8 million years ago, Ma). However, the effects of these changes on interactions among organisms have been little studied. Here, I compile a detailed record of insect herbivory on angiosperm leaves for the Bighorn Basin of Wyoming and investigate the causes of variation in insect herbivory. I test whether the changes in temperature, atmospheric carbon dioxide, and floral diversity observed across the Paleocene-Eocene boundary correlate with changes in insect damage frequency, diversity, and composition. Because these correlations cannot be recognized without regional, high-resolution studies, this thesis makes a major contribution to the ecological understanding of disturbance and biotic response.;Insect damage censuses were conducted at nine stratigraphic levels ranging in age from 59 to 52.5 Ma. A total of 9071 fossil angiosperm leaves belonging to 107 species were examined for the presence or absence of 71 DTs. Damage frequency, diversity, and composition were analyzed on the bulk floras and individual host species. Chapter 1 focuses on insect herbivory during the Paleocene-Eocene Thermal Maximum (PETM). The abrupt global warming and increase in atmospheric CO2 during the PETM make it the best geologic analog for modern anthropogenic warming. Chapter 2 examines small-scale spatial variability in insect damage along two early Eocene carbonaceous shale beds. I test whether spatial variability within a bed exceeds differences between beds. Chapter 3 extends the study interval through the early Eocene Cool Period and into the Eocene Thermal Maximum, when temperatures cool and then warm to a sustained Cenozoic maximum.;Temporal trends in insect damage are generally greater than intra-bed variation, which is primarily due to differing floral composition. The Bighorn Basin dataset shows a very strong positive correlation between damage diversity and temperature. Damage diversity increases as temperature increases through the late Paleocene, peaks in the PETM, decreases during the early Eocene cooling, and then increases again during the warming to the sustained Eocene Thermal Maximum. Temperature probably affects insect herbivory by allowing diverse insect populations from lower latitudes to migrate northwards and by influencing insect metabolism and population density.