COMPARISONS OF ECOSYSTEM DYNAMICS BEFORE AND AFTER INVASION REVEAL CONSEQUENCES OF INVASIVE SPECIES IN BENTHIC MARINE PALEOCOMMUNITIES

Although a leading cause of extinction today, the effects of biotic invasions remain poorly understood. In light of the current biodiversity crisis, a thorough understanding of how communities respond to extreme changes is essential to manage and restore ecosystems.

Here we utilized comparative network modeling to identify changes in Late Ordovician marine paleocommunity structure and functioning after asymmetrical biotic interchange in the Cincinnati region (USA) known as the Richmondian Invasion (RI). Cascading Extinctions on Graphs models employ serial deletion of primary producers resulting in cascading secondary extinctions, which can be used to assess paleocommunity dynamics. The post-RI community was less resistant and stable, with a lower collapse threshold, frequent complete collapse, and more variable response to perturbation. We hypothesize that the greater resistance to secondary extinction in the pre-RI paleocommunity was due to the prevalence of detrital food-chains, which can persist indefinitely. The loss of 3 detritivore guilds post-RI may have disrupted detritus based food-chains, leading to destabilization. Richness decreased after the RI from 358 to 239 species, corresponding to the loss of guilds and trophic links. The RI may, therefore, have reduced functional richness, and the arrival of new taxa did not equate to an increase in the types of interactions between organisms.

Arctic and Antarctic benthic marine ecosystems are functionally analogous to the Paleozoic communities examined, dominated by suspension feeders and lacking durophagous predators. These communities are expected to undergo widespread invasions with rising ocean temperatures. These results suggest that Antarctic ecosystems are likely to destabilize if invaders have disproportionately large effects on detritus-based trophic chains. These findings warrant additional investigation, and underscore the importance of detritus-food chains in benthic marine communities.