23-2 Assessing diversity trends and ecological interactions among native and invasive taxa during the Late Ordovician Richmondian Invasion in the Nashville Basin

Session: Phylogenetic and Computational Approaches in Paleobiology and Paleoecology, Part I

Presenting Author:

Authors:

Abstract:

Biotic immigration events can profoundly reshape ecosystems by altering biodiversity patterns, community structure, and ecological interactions. One of the most prominent fossil examples is the Late Ordovician (Katian) Richmondian Invasion, during which more than 60 genera, including brachiopods, bryozoans, mollusks, and corals, expanded into the Eastern Laurentian Basin. This invasion initiated major changes to marine paleocommunities and is well recorded in the stratigraphic successions of Cincinnati, Ohio, and Nashville, Tennessee. The Richmondian Invasion is considered a coordinated biotic invasion, where multiple taxa entered a region at the same time, leading to lasting ecological shifts. Coordinated invasion events typically influence species richness, evenness, dominance, and niche partitioning, ultimately affecting biomass distribution and community organization.

Although the Richmondian Invasion has been studied extensively in the Cincinnati Basin, its ecological and taxonomic impacts in the Nashville Basin are less understood. This study aims to address that gap by examining diversity change and interactions among ecological groups in the Nashville region before, during, and after the invasion. For analysis, taxa were categorized as native specialists, native generalists, invasive specialists, and invasive generalists. Stratigraphically constrained species occurrence data were compiled from published literature, online databases such as PaleoDB and iDigBio, and newly conducted fieldwork. To explore diversity trends and species interactions among groups, we used PyRate, a Bayesian framework that estimates speciation, extinction, and preservation rates from fossil occurrence data. Within PyRate, we applied the Multivariate Birth–Death (MBD) model to evaluate whether the diversity of one ecological group, such as invasive generalists or native specialists, influenced the origination or extinction of other groups.

The results show substantial diversity shifts in the Nashville Basin across the Richmondian Invasion. Native taxa declined, while invasive groups, particularly generalists, increased in diversity. Invasive generalists suppressed the origination and promoted the extinction of native generalists, likely due to overlapping niches and differences in ecological tolerance. Despite these impacts, the overall increase in genus-level standing diversity may have supported greater ecosystem stability, as invaders contributed to more complex food webs and increased functional diversity.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10269

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