Paper No. 4
Presentation Time: 9:45 AM
CONFAMILIAL PREDATION ON NATICID GASTROPODS THROUGH A PULSED EXTINCTION IN THE PLIO-PLEISTOCENE OF THE CAROLINAS
SMITH, Jansen A., Department of Geology, Macalester College, 1596 Hague Avenue, Saint Paul, MN 55104, DIETL, Gregory P., Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, NY 14850-1398, KELLEY, Patricia H., Department of Geography and Geology, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC 28403-5944, CHRISTIE, Max, Geology, Pennsylvania State University, 434 Deike Building, University Park, PA 16802, LOCKWOOD, Rowan, Department of Geology, The College of William and Mary, P.O. Box 8795, Williamsburg, VA 23187 and LAYOU, K.M., Department of Geology, College of William and Mary, P.O. Box 8795, Williamsburg, VA 23187, jsmith12@macalester.edu
During the Plio-Pleistocene, a two-pulsed extinction occurred among western Atlantic molluscs. Although taxonomic turnover related to the extinctions has been studied, accompanying ecological effects have been neglected. This study examined the effects of the turnover episodes on confamilial predation in shell-drilling naticid gastropods, an easily quantified predator-prey interaction that is well preserved in the fossil record. Drilling frequency (DF) and relative abundance of confamilial and alternative prey were compared across the extinctions in order to investigate changes in the ecological interaction within the community and specifically in naticid confamilial predation. Recent experiments have shown low frequencies of cannibalism result from high risk ecological conditions (Gould et al., 2010). Thus, DF on naticids is expected to increase after the extinctions, corresponding to a less risky environment (Dietl et al., 2004).
Naticids from eighteen localities in the Pliocene Duplin Formation and the Pleistocene lower and upper Waccamaw Formation of the Carolinas were used to test this hypothesis. Specimens were examined for drill holes, and DF was determined for each formation. The Duplin Formation is characterized by a DF of 0.04 (n=340), while both the lower (n=1628) and upper (n=260) Waccamaw Formation are characterized by a significantly higher (p<0.01) DF of 0.14. When DF is calculated for specific size ranges of naticids, the most populated bin (16-25 mm) shows a significant successive increase (p<0.05) in DF between the Duplin (0.05), lower Waccamaw (0.15), and upper Waccamaw (0.27). These data indicate that the environment following the extinctions was less risky than pre-extinction conditions.
Unstandardized DF rankings of alternative prey for two localities in the pre-extinction Duplin and two post-extinction lower Waccamaw localities show an abundance of alternative prey. These rankings were size standardized using geometric mean to account for variability in prey size between genera. In the most populated bin (10-25 mm), naticids always ranked in the lowest two-thirds of preyed upon taxa. These results support the conclusion that increased predation on naticids was not caused by a decrease in alternative prey, but was due to a lower risk environment.
