Research: Ecosystem impacts in the Ordovician due to species migration

Contrasting ecosystem impacts of biotic invasions in the Type Cincinnatian Series (Late Ordovician, Katian) by Alycia L. Stigall and Ron Fine 

Article summarized by Jen Bauer. Dr. Alycia Stigall is a professor at Ohio University and Mr. Ron Fine is an avocational paleontologist associated with the Dry Dredgers.

From the authors: This project is an excellent example of how long term collaborations between amateur and professional paleontologists can result in exciting science. Ron was able to connect a series of unusual fossil occurrences that he has collected over many years with Alycia’s long term research program on invasive species. We were able to work together to demonstrate that species invasions occurred at multiple intervals with varying impacts on the Cincinnati ecosystem.  This is an exciting result that allows us to validate modern invasive species theory with real-life observations of invasive processes in Earth’s past.

Figure 1: Classic Cincinnatian outcrop at a location in Kentucky. Image Credit: Jen Bauer

The fossil record allows for scientists and researchers to explore where and when organisms would have lived in the past. This information can be very useful for understanding ecosystem dynamics, migrations through time, and much more. The Late Ordovician of the Cincinnatian Arch (tri-state region of Ohio, Indiana, and Kentucky) provides an excellent case study to begin examining the effects of species migration in deep time. The clearly layered rock is a textbook example of stratigraphic succession (see Figure 1).  

Figure 2: Rock units distinguished in terms of relative geologic time in the Late Ordovician. Richmondian Invasion noted by the gold box on the right. The colored units are those affected by the invading organisms. Image from the Ordovician Atlas drafted by H.M.R. Brame.

Of interest to scientists and researchers, is the detailed information gained from the relatively continuous time represented in these rock layers. A comprehensive analysis of the organisms present aids in understanding ecosystem and community dynamics. A well-documented biotic invasion event is recorded in the rocks of this region (see Figure 2) called the Richmondian Invasion. Invasive species migrated in ancient oceans when sea level rose high enough to allow the transport of larval stage organisms out of their original ocean basins and enter a new one that they did not previously inhabit. Studies can be conducted to assess what happens to the original organism population once these new species enter their basin.  

Figure 3: Brachiopods from the classic Richmondian Invasion fauna. The two new species are in the same genera as these two: Leptaena (left) and Holtedahlina (right). Images from Ordovician Atlas.

Expert collectors from the Dry Dredgers, including co-author Ron Fine, have noted that some of the organisms that are considered classic Richmondian invaders can be found much earlier than the notable invasion event. Detailed collecting uncovered two brachiopod species that appear in low abundance before the larger invasion interval. The appearance of these species suggests there were brief periods of sea level rise allowing for external species to enter the basin. These species were low in abundance, but their presence is important to understanding overall ecosystem dynamics during this time period. The conclusions of this work provide evidence that unlike the Richmondian Invasion, this smaller invasion did not change the overall ecosystem structure as evidenced by the very stable marine communities.  

References

Bauer, J.E. and Stigall, A. L. 2014. Phylogenetic paleobiogeography of Late Ordovician Laurentian brachiopods. Estonian Journal of Earth Science, 63(4). Open Access.

Stigall, A. L. 2013-2015. Atlas of Ordovician Lifewww.ordovicianatlas.org; Richmondian Invasion information; Geologic Setting information; Ordovician Outcrop Belt information.

Stigall, A.L. and Fine, R. 2018. Ecosystems impacts of biotic invasions in the Type Cincinnatian Series (Late Ordovician, Katian). Palaeoworld. doi: 10.1016/j.palwor.2018.04.004

Stigall, A. L., Bauer, J. E., Brame, H-M. R., 2014, The Digital Atlas of Ordovician Life: Digitizing and mobilizing data for paleontologists and the public. Estonian Journal of Earth Sciences, 63: 312-316. Open Access.