UNDERSTANDING THE EFFECTS OF INVASIVE SPECIES ON SHALLOW MARINE FOOD WEB STRUCTURE DURING THE LATE ORDOVICIAN (KATIAN) RICHMONDIAN INVASION

Invasions by non-native taxa can be difficult to study today as ecosystems are typically only monitored after an invasion has already begun. The fossil record is an invaluable tool that can be used to examine an ecosystem before and after the arrival of invaders. The Richmondian Invasion is a well-documented incursion of marine species that occurred during the Late Ordovician (Katian) approximately 451 to 446 million years ago. Invasions are thought to trigger significant ecosystem restructuring and major changes in energy transfer pathways, such as changes in patterns of interactions and the distribution of taxa among trophic levels in the food web. We examined 1,285 species to reconstruct six shallow marine food webs from the Richmondian Invasion of the Cinnicinati Arch. Food webs were examined during the arrival, establishment, and integration invasion phases to identify any changes in structure and functioning. We hypothesize that if invaders successfully integrated into the ecosystem, they should forge new consumer resource relationships with functional groups that were already present or give rise to novel functional groups. Invasive species present in the basin were identified through an extensive literature search, and their effects on food web structure across the invasion phases were evaluated by comparing various food web properties of guilds with and without invaders, including network trophic position (ntp) and species richness within guilds. Results indicate a relationship between guild richness and ntp during each sequence (R = 0.082 to 0.20 , p << 0.0025) with low diversity in guilds at higher trophic positions. The proportion of invaders increases throughout the Richmondian Invasion and invaders are not limited to specific guilds. These preliminary results are surprising as changes in community composition suggest that invasions cause major restructuring of the ecosystem, however, our initial comparisons representing direct tests of ecosystem structure show very little structural change. Our findings suggest that in shallow benthic ecosystems, on evolutionary timescales, it may be more important to track the types of functions invaders perform as opposed to changes in community composition or species diversity. Knowing how this ecosystem responded to invaders allows modern biologists to better predict and respond to future ecosystem changes.