NICHE BREADTH, GEOGRAPHIC RANGE SIZE, AND MOLLUSKAN SURVIVORSHIP ACROSS THE K-PG BOUNDARY IN THE U.S. GULF COASTAL PLAIN

Mass extinction events significantly alter the course of ecological and evolutionary change. To better understand the effects of mass extinctions on the biosphere, it is important to explore relationships between extinction patterns and niche dynamics. This study tests the hypothesis that shallow marine taxa with larger niche breadths and geographic range sizes were less susceptible to loss of suitable habitat across the Cretaceous-Paleogene (K-Pg) boundary, and that these taxa preferentially survived into the Danian. Marine mollusk fossil occurrences and paleoenvironmental data (derived from sedimentological and global climate model data) from the U.S. Gulf Coastal Plain were used to build regional scale paleoecological niche models (PaleoENMs) via two methods: (1) Ellipsoid envelope models were constructed to quantify niche breadth (mean ellipsoid volume) and suitable habitat area (mean prevalence) in geographic and environmental space; (2) Maximum entropy (Maxent) models were constructed using the same data to obtain predicted geographic range size estimates. Models trained in the Maastrichtian were projected to Danian environments to see how predicted niche dimensions of taxa changed across the K-Pg boundary. Maxent and ellipsoid PaleoENMs show apparent decreases in mean prevalence and range size for most taxa when projected into the Danian. However, preliminary results do not indicate a standard relationship among niche breadth, range size, magnitude of suitable habitat loss, and survivorship across the K-Pg. This suggests that species’ biogeographic patterns across this extinction event were more complex than simple macroecological traits such as niche breadth and geographic range. Additional important factors such as biotic interactions or dispersal capacity and/or species-specificity may have also played a role in response to environmental change during the K-Pg.