BIOTIC INVASION AND THE ASSEMBLY OF REGIONAL ECOSYSTEMS IN DEEP TIME

Biotic invasions play a central role in the assembly of regional ecosystems because they help determine local and regional diversity, taxonomic composition, and gradient structure. Understanding the processes underlying invasions in deep time requires a well-constrained time-environment framework from at least two areas, the source area of the invading taxa and the area that receives the invading taxa. Here we compare Late Ordovician diversity, taxonomic composition, and gradient structure between a purported source region (Bighorn Mountains, western USA) and an area affected by an invasion (Cincinnati Arch, eastern USA). We aim to answer the question, whether the invasion resulted in a homogenization of faunal composition and diversity between the two regions? Faunal data come from collections tied to measured sections and span shallow and deep subtidal environments of correlative stratigraphic sequences of approximately 1 myr duration. Following the invasion, both local and regional diversity was approximately seventy percent higher in the Bighorn Mountains compared to the Cincinnati Arch. Of 115 total taxa in the two regions, only 36 are shared indicating that significant taxonomic differences were still maintained after the invasion. Among these shared taxa, preferred environment, average abundance of taxa in samples, and occupancy correlate weakly between regions indicating strong differences in gradient structure. Taken together, these preliminary data suggest that the biotic invasion in the eastern USA was not simply an expansion of ecological structure from the source region as exemplified by the tropical environments of the Wyoming, rather the invasion appears to have involved only certain taxa and a much broader region of tropical Laurentia.