ARONOWSKY, A.; Univ. of California, Berkeley: Differences in observed and calculated predation intensities for the prey of naticid gastropods: implications for predator-prey paleoecology.

Predation is posited as a driving evolutionary force in the marine realm, and a multitude of ecological and paleontological studies focus on the activities of drilling gastropods such as naticids. Naticid drillholes are beveled structures, and as such have two diameters; the inner (IBD) and the outer (OBD). Drillholes with an IBD:OBD ratio less than 0.5 are traditionally interpreted as non-functional because at these ratios the inner hole supposedly is not big enough for the predator to feed. Incomplete drillholes are traditionally interpreted as unsuccessful attempts by predators, with the unfinished drillhole interpreted as successful escape by the prey. Measures of predation intensity incorporate only complete drillholes with IBD:OBD ratios greater than 0.5. Six months of observation of predation and feeding by the temperate western Atlantic naticids, Euspira heros and Neverita duplicatus, revealed new insights into the consumption of prey. This study found that naticids consumed prey bearing incomplete drillholes, complete drillholes with IBD:OBD ratios ranging from 0.28-0.72, and no evidence of predation at all (undrilled). Observed predation intensities for both taxa were significantly higher than predation intensities calculated using traditional methods. This suggests that previous estimates of naticid predation based on collections of empty shells are potentially highly inaccurate. Recommendations for increasing the accuracy of calculated predation intensities are provided based on behavioral observations and extant phylogenetic bracketing.