USING FOOD WEBS TO UNDERSTAND THE EFFECTS OF BIOTIC INVASION ON LATE ORDOVICIAN MARINE COMMUNITY STRUCTURE

The long-term effects of biotic invasions on modern ecosystems, including extinction, remain poorly understood. While often examined using richness and relative abundance metrics, these do not capture changes in ecosystem complexity and dynamics, which long-term data pre-dating anthropogenic activities are lacking. Food webs provide an alternative ecosystem perspective, capturing changes in energy transfer and species interactions. Furthermore, paleocommunity data are appropriate for food web reconstruction, and can thus provide insights into ecosystem conditions persistent over evolutionary timescales.

To further understand long-term invasion dynamics, food webs were reconstructed from Late Ordovician (Cincinnatian) marine paleocommunities before and after the Richmondian Invasion, an influx of invasive species to the Cincinnati region (USA). Food web networks were compared before and after the invasion to identify any resultant changes in ecosystem structure that may have occurred. Network structure was examined using functional richness, connectance, proportion of omnivory, modularity, and trophic level distribution.

Post-invasion food webs exhibited a decrease in the number of functional groups, from 30 to 27. Connectance, the relative amount of interactions between guilds, decreased from 0.1033 to 0.1015, suggesting little to no change in overall ecosystem complexity. This result may be associated with a decreased proportion of omnivores, from 50% to 44%. Furthermore, the number of trophic levels decreased after the invasion from 7 to 6, indicating potential functional homogenization. Shorter trophic chain lengths could allow negative effects to spread rapidly through the network, indicating lowered resilience and stability after invasion, although additional quantitative tests are needed.

These results have important consequences for conservation and management efforts, which typically focus on preservation of biodiversity, suggesting that functional richness may play a more critical role in ecosystem stability and persistence.