Richmondian Invasion

Invasive Species
The spread of invasive species (such as zebra mussels in the Great Lakes) is a major cause of damage to modern ecosystems. Modern species invasions result in biodiversity decline due to increased competition with and local extinction of native species. While invasive species are a major threat to modern ecosystems, the long term (thousands of years or more) impacts of species invasions are poorly constrained because they fall outside the timescale available for study by biologists and ecologists.

Species invasions, however, are not unique to the present; episodes of intense invasion have also occurred in the geologic past, albeit without human intervention. Studying species invasions in the fossil record provides a way to assess the long-term effects that the modern wave of species invasions will have on our planet.

To study how the spread of these invasive species affected the native, species-level biogeographic patterns were reconstructed and analyzed for brachiopod species during the Richmondian Invasion–an episode of intense invasion preserved in the Late Ordovician strata of the Cincinnati, Ohio region–as an analog for modern invasion dynamics.

Impact of the invaders
The Maysvillian-Richmondian boundary coincides with an invasion of species from the Midcontinent into the Cincinnati region. The invaders included all types of animals including brachiopods, bryzoans, and even corals. In fact, no coral species lived in the Cincinnati rocks until after the Richmondian invasion.

Detailed gradient ecology and biofacies analyses by Steve Holland (Univ. Georgia) and Mark Patzkowsky (Penn State Univ.) indicated that the C1 to C3 pre-invasion communities exhibited high levels of similarity in community structure. The C4 sequence preserves a fundamental restructuring of biofacies (groups of taxa that occur in association) in which the onshore-offshore gradient breaks down and faunal differentiation diminishes. Well-defined biofacies are restablished only during the C5 sequence, although C5 biofacies differ significantly from those of the Maysvillian due to the ecological dominance of many invader taxa. Holland & Patzkowsky emphasized community composition at a genus level. Paleobiogeographic studies by Alycia Stigall (Ohio University) and her students, expand on this work by analyzing patterns of biogeographic distribution at the species level.

Biogeographic analyses indicate a key determinant in faunal turnover was the differential survival of ecological generalist taxa compared to ecological specialists during and after the Richmondian Invasion interval. As noted on individual atlas pages, most of the native Cincinnatian species that persisted through the invasion interval occupied broad ecological niches and they could tolerate a wide range of environmental condition,.  The newly introduced invasive taxa also had broad ecological tolerances.  Highly specialized native species were less effective at acquiring resources in this invasive regime and became extinct.

Notably, both the native and invasive generalist species demonstrate morphological adaptation as demonstrated by Lindsey Leighton and Carrie Tyler (Univ. Calgary) and by consolidating their preferred environment into a smaller set of ecological tolerances (Stigall Lab).

The research on the Richmondian Invasion, therefore, suggests that competition between native and invasive species may have an important impact on the future development of our modern ecosystem.

To watch a Science Cafe lecture by Dr. Alycia Stigall about the Richmondian Invasion and its lessons for today’s ecosystem, click here for the Livestream archive.