A number of times during life's history, biodiversity was decimated by mass extinctions that wiped out a large proportion of the Earth's species. The five largest mass extinctions of the prehistoric world are known as the "Big Five" (the dinosaurs died out in the fifth and most recent), and the present-day, human-induced extinction has been called the "Sixth Extinction". This ongoing extinction, along with the environmental changes that are causing it, will have important effects on biological communities in the coming decades?for example, as the climate changes and as competitors or predators go extinct, species' geographic and ecological ranges may shift, leading to new communities composed of unexpected combinations of species. We would like to predict the nature of these changes?after all, these communities provide us with habitat and resources, and the shifting of species has important economic consequences. One way to forecast biotic responses to extinction and environmental change is to study past responses to similar changes?that is, to study mass extinctions in the fossil record. Did extinctions simply produce "thinned out" communities that were similar to previous ones, merely with some species removed? Or did species expand into new habitats and ecological niches once predators and/or competitors were eliminated? Perhaps a changing environment produced communities composed of novel combinations of species. Some mass extinctions were probably too large and catastrophic to provide close analogues to the modern world (e.g., the Permian-Triassic extinction); a less severe extinction in which a greater proportion of species survived provides a more direct model. The Late Devonian extinction (specifically, the event at the Frasnian-Famennian boundary) provides a reasonable comparison, and this project will contrast fossil assemblages that formed before and after the extinction. Collected in New York and Pennsylvania, these assemblages are the fossilized remains of communities that lived in a shallow sea that covered the area in the Devonian. PIs will combine ecological gradient analysis with a sedimentological analysis to document the environments in which each species lived before and after the extinction, and any changes through time. They will also examine any changes in co-occurrence patterns among species. The results will cast light not just on biotic changes in the Devonian, but also, hopefully, on those in the coming century.
