ASSESSING THE IMPACT OF THE LATE ORDOVICIAN RICHMONDIAN INVASION IN THE NASHVILLE DOME USING ECOLOGICAL NICHE MODELING

The Richmondian Invasion records the immigration of a diverse suite of marine taxa into southeastern Laurentia during the Late Ordovician (Katian) and is preserved in the strata of Cincinnati Basin and Nashville Dome of Eastern North America. The evolutionary and ecological impact of the invasion has been well studied in the Cincinnati region; however, faunal change in the Nashville Dome is more poorly constrained. In this study, the impact of the Richmondian Invasion on the biota of the Nashville dome will be quantified by assessing niche stability through time.

Late Ordovician strata of the Nashville Dome comprise highly fossiliferous limestone and shale units. Fossils are abundant and distributed across a large geographic area, which provides a robust framework on which to apply Paleo-Ecological Niche Modeling (PaleoENM) to quantify the amount of change in species’ niches between the before, during, and after the invasion interval. In-situ data were collected in the field to gather both occurrence/absence data for different fossil taxa and environmental proxy data for niche modeling. Niche models were developed using MAXENT, an R-based modeling package. Taxa modeled exhibited at least seven geographically discrete occurrence points among twenty field locations spanning the western edge of the Nashville Dome. Articulated brachiopods are the most abundant and easily identified fossils, thus they comprise the bulk of the species modeled. Bryozoans, gastropods, and a few other benthic taxa are also very diverse and appropriately abundant for modeling.

By modeling the environmental parameters as they change through time and the distribution of taxa with well understood niches, it is possible to characterize change in species niche dimensions across this invasion event in the Nashville Dome. Comparing these results with similar analyses previously conducted for taxa of Cincinnati region permits analysis of how species responses to the Richmondian Invasion varied among basins. Quantifying niche stability and comparing the similarities between different stages of the invasion provides a broader picture of this event within geographic space and improving the current understanding of how Biotic Immigration Events alter ecological systems in geologic time.