Ecological Niche Modeling of Richmondian (Late Ordovician) Brachiopods in the Cincinnati Arch: Early Stages of a Biotic Invasion

Within the Cincinnati, Ohio region, the beginning stages of a large-scale biotic invasion is recorded the C4 depositional sequence, which includes the Arnheim Formation and its correlates (Late Ordovician, Richmondian Stage). During the first half of the C4 sequence, faunal turnover is low and community assemblages resemble to those of underlying the C2 and C3 sequences. Midway through the C4 sequence, however, invasive fauna from western Laurentia enter the region and faunal turnover rates increase. The fauna and strata of this region are well studied and the ecological changes present in these strata present a unique opportunity to study biogeographic changes associated with the onset of a biotic invasion.

In this study, GIS-based ecological niche modeling is used examine the biogeographic and paleoecological impact of the early stages of this invasion. Brachiopods are abundant throughout the sequence and are used as model organisms. Species niches are modeled based on known species occurrence data in concert with a set of environment conditions as derived from sedimentological variables. The spatial extent of species ranges will be assessed at three temporal intervals during the C4 sequence (Arnheim Formation) of the Richmondian Stage, which provides a framework to assess biogeographic responses of native and invasive species as the invasion progresses.

Geographic ranges for individual species are modeled based on the ecological characteristics of their fundamental niche. The resulting models are subjected to spatial analysis to assess both size and location of each species' range at each time slice and the relative change in those parameters through time. Results indicate that invader taxa initially occupy small ranges that expand through the sequence, and native species that occupy restricted geographic ranges will become extinct by the end of the sequence, while those with larger ranges survive.