Invasion and interaction: diversity shifts in the Nashville Basin during the Late Ordovician Richmondian Invasion

Biotic immigration events significantly reshape ecosystems and community structures, yet their long-term evolutionary patterns remain understudied. One of the better studied ancient marine invasions is the Late Ordovician Richmondian Invasion in eastern Laurentia, which is expressed in both the Cincinnati and Nashville Basins. Prior studies have focused on the Cincinnati region with no previous quantitative comparisons of the invasion impacts between basins. Herein, we analyse generic occurrence data for marine invertebrates to reconstruct diversification and interaction dynamics across the Richmondian Invasion in the Nashville Basin. Origination and extinction were estimated with PyRate, and diversity-dependent interactions among native generalist, native specialist, invasive generalist, and invasive specialist groups were inferred using Multivariate Birth–Death models. Invaders, mostly generalists, first appear in the C4–C5 sequences. Despite small declines in native genera, the addition of invasive taxa increased total diversity post-invasion. Model results show strong self-suppression of origination within most groups, which is consistent with the broad ecological niches of generalists reducing opportunities for reproductive isolation and origination. For invaders, this also reflects competition between established cohorts and new arrivals. Cross-group effects indicate that invasive generalists suppress origination and elevate extinction of native generalists, both signatures of competitive interaction. Collectively, these patterns support selective turnover and tighter competitive connectivity among low-trophic invaders, not whole ecosystem collapse, which is similar to patterns reported from the Cincinnati region. Overall, the Nashville Basin records an invasion-driven reorganization that increased taxonomic richness while imposing selective losses on native taxa, illustrating how interaction networks regulate diversification during coordinated immigration events.