PLANT AND INSECT HERBIVORE COMMUNITY VARIATION ACROSS THE PALEOCENE-EOCENE BOUNDARY, HANNA BASIN WY

Ecosystem function and stability are highly affected by internal and external stressors. Utilizing paleobotanical data gives insight into evolutionary processes that an ecosystem undergoes across long periods of time, allowing for a more complete understanding of how plant and insect herbivore communities are affected by ecosystem imbalance. Basal trophic levels are more sensitive to changes within an environment thus recording the overall fitness of an ecosystem (Wilf 2008). To study how plant and insect herbivore communities change during times of instability and disturbance, we quantified community turnover across the Paleocene-Eocene boundary in the Hanna Basin, southeastern Wyoming. This particular location is unlike other Laramide basins because it has an abundance of coal layers and paucity of red beds, suggesting perpetually high water availability.

We sampled approximately 800 semi intact dicot leaves from five stratigraphic levels, one of which is likely during the recovery phase of the Paleocene-Eocene Thermal Maximum. Field collections were supplemented with specimens at the Denver Museum of Nature & Science to increase temporal range. Fossil leaves were classified into morphospecies and herbivore damage was documented on each leaf. We tested for changes in plant and insect herbivore diversity using rarefaction and community composition using NMDS ordinations. We also documented changes in depositional environment at each stratigraphic level to better contextualize the environment of the basin. Plant diversity was highest at the oldest Paleocene sites and decreased into the Eocene, whereas damage diversity was higher at the sites with low plant diversity. Plant communities experience a complete turnover during the PETM recovery zone and do not return to pre-PETM composition. Insect herbivore communities turn over during the PETM, but, unlike plant communities, rebound to their pre-PETM structure. These results suggest that insect herbivore communities respond more strongly to plant community composition than to the diversity of species present.