USING ENVIRONMENTAL NICHE MODELING TO ASSESS THE ROLE OF CHANGING SPECIES RANGES DURING THE LATE DEVONIAN BIODIVERSITY CRISIS: A CASE STUDY FROM THE APPALACHIAN BASIN

The Frasnian-Famennian (Late Devonian) biodiversity crisis was a time of dramatic biodiversity decline associated with expanding geographic ranges of species and interbasinal invasions. Quantification of the geographic changes in species ranges can further our understanding of this complex crisis. In this analysis, geographic ranges are estimated for brachiopod and bivalve species during the late Middle (mid-Givetian) to the middle Late Devonian (terminal Frasnian) to investigate range changes during the time leading up to and including the Late Devonian biodiversity crisis. Species ranges were predicted using GARP (Genetic Algorithm using Rule-set Prediction), a modeling program developed to predict fundamental niches of modern species. This method was applied to fossil species to examine changing ranges during a critical period of Earth’s history.

Comparisons of GARP species distribution predictions with historical understanding of species occurrences indicate that GARP models predict accurately the presence of common species in some shallow marine depositional settings. In addition, comparison of GARP distribution predictions with species-range reconstructions from GIS analysis suggests that GARP modeling has the potential to predict species ranges more completely and tailor ranges more specifically to environmental parameters than GIS methods alone. Thus, GARP modeling is a potentially useful tool for predicting fossil species ranges and can be used to address a wide array of paleontological problems.

The use of GARP models allows a statistical examination of the relationship of geographic range size with species survival during the Late Devonian. Large geographic range was statistically associated with species survivorship across the crisis interval for species examined in the linguiformis conodont zone but not for species modeled in the preceding varcus or punctata zones. The enhanced survival benefit of having a large geographic range, therefore, appears to be restricted to the biodiversity crisis interval.