CHANGES IN TAXONOMIC AND FUNCTIONAL ECOLOGY NORTH OF A BIOGEOGRAPHIC BOUNDARY DURING THE PLIOCENE TO MODERN, WESTERN NORTH ATLANTIC

Previous work has shown that large taxonomic extinction does not always correspond to large ecological or functional changes. This distinction is important because ecosystems that are initially resistant to extinction can collapse when ecological functions are eliminated. Although other workers have looked at changes in taxonomic diversity in the Western North Atlantic, changes in the functional or ecological diversity remain unknown. Our goal is to assess the effects of the Plio-Pleistocene extinction both taxonomically and ecologically, north of the modern biogeographic boundary at Cape Hatteras, North Carolina where diversity did not recover. To do this, we collected a new dataset of marine mollusks from Virginia and North Carolina. We identified these specimens to the species level to assess the taxonomic effects of the Plio-Pleistocene extinction, and as guilds (a group of organisms that utilize resources in a similar way) to assess the ecological effects. These changes were evaluated using additive diversity partitioning, cluster analyses, ordination, and relative abundance distributions. Although taxonomic diversity, gradient structure, and relative abundance structure changed greatly from the Pliocene to Pleistocene, the same analyses on the guild dataset were similar before and after the extinction. This suggests that the Plio-Pleistocene extinction did not have large ecological effects among mollusks. In addition, large differences in multivariate analyses were seen among pre- and post-extinction open marine samples, indicating high taxonomic turnover. Pre- and post- extinction marginal marine samples, however, were similar, indicating low taxonomic turnover. This suggests that the extinction was more pronounced in open rather than marginal marine settings.