Plant and insect herbivore community variation across the Paleocene-Eocene boundary in the Hanna Basin, southeastern Wyoming

Lauren E Azevedo Schmidt; Regan E Dunn; Jason Mercer; Marieke Dechesne; Ellen D Currano

doi:10.7717/peerj.7798

Plant and insect herbivore community variation across the Paleocene-Eocene boundary in the Hanna Basin, southeastern Wyoming

PeerJ. 2019 Oct 15:7:e7798. doi: 10.7717/peerj.7798. eCollection 2019.

Authors

Lauren E Azevedo Schmidt¹, Regan E Dunn², Jason Mercer¹, Marieke Dechesne³, Ellen D Currano^{1

4}

Affiliations

¹ Botany, University of Wyoming, Laramie, WY, USA.
² Natural History Museums of Los Angeles County, La Brea Tar Pits, Los Angeles, CA, USA.
³ U.S. Geological Survey, Geosciences and Environmental Change Science Center, Denver, CO, USA.
⁴ Geology and Geophysics, University of Wyoming, Laramie, WY, USA.

Abstract

Ecosystem function and stability are highly affected by internal and external stressors. Utilizing paleobotanical data gives insight into the evolutionary processes 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. To study how plant and insect herbivore communities change during times of disturbance, we quantified community turnover across the Paleocene--Eocene boundary in the Hanna Basin, southeastern Wyoming. This particular location is unlike other nearby Laramide basins because it has an abundance of late Paleocene and Eocene coal and carbonaceous shales and paucity of well-developed paleosols, suggesting perpetually high water availability. We sampled approximately 800 semi-intact dicot leaves from five stratigraphic levels, one of which occurs late in the Paleocene-Eocene thermal maximum (PETM). Field collections were supplemented with specimens at the Denver Museum of Nature & Science. Fossil leaves were classified into morphospecies and herbivore damage was documented for each leaf. We tested for changes in plant and insect herbivore damage diversity using rarefaction and community composition using non-metric multidimensional scaling ordinations. We also documented changes in depositional environment at each stratigraphic level to better contextualize the environment of the basin. Plant diversity was highest during the mid-late Paleocene and decreased into the Eocene, whereas damage diversity was highest at the sites with low plant diversity. Plant communities significantly changed during the late PETM and do not return to pre-PETM composition. Insect herbivore communities also changed during the PETM, but, unlike plant communities, rebound to their pre-PETM structure. These results suggest that insect herbivore communities responded more strongly to plant community composition than to the diversity of species present.

Keywords: Climate change; Fossil record; Hanna Basin; Insect damage; PETM; Paleobotany; Paleoecology; Paleontology; Plant and insect interactions.

Grants and funding

This work was supported by the National Science Foundation (No. EAR145031), the Paleontological Society and the University of Wyoming. Funding for stratigraphic mapping was obtained by the U.S. Geological Survey, National Cooperative Geologic Mapping Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.