USING FOOD WEBS TO EXAMINE ECOSYSTEM DYNAMICS DURING BIOTIC INVASIONS IN LATE ORDOVICIAN SHALLOW MARINE COMMUNITIES

Although they are the leading cause of extinction in modern ecosystems, relatively little is known about the long-term effects of invasive species. Biotic invasions can alter trophic interactions, richness, predation intensity, ecospace utilization, and faunal dominance. Food webs provide an alternative strategy to evaluate energy transfer and interactions among species, and can be applied to the fossil record to evaluate paleocommunity vulnerability and response to invasion.

To quantify the effects of biotic invasions on ecosystem structure, food webs were reconstructed from Late Ordovician (Cincinnatian) marine paleocommunities before and after the Richmondian Invasion (RI), an influx of invasive species to the Cincinnati region (USA). Food webs were reconstructed by combining bulk field sampling, and museum collections surveys from the Fairview and Liberty Formations (pre- and post-invasion respectively). Species were assigned to ecological guilds based on functional morphology, autecological data, and the literature to construct guild-level metanetworks representing trophic interactions.

Metanetwork connectance and modularity were used to evaluate differences between ecosystem structure and complexity. Although the RI is thought to have increased regional richness by as much as 40%, we did not observe a notable increase in functional diversity (i.e., number of guilds), as invaders populate pre-existing guilds. Furthermore, the RI does not result in an increase of functional interaction diversity. Although not conclusive, this suggests that there may be no difference in complexity between pre- and post-invasion paleocommunities. Comparison of perturbation thresholds will be used to examine community robustness, and may reveal differences in resilience and stability between incumbent and post-invasion communities. If pre-invasion communities are less resilient or stable, this may have allowed invaders to succeed.