VALIDITY OF TAXON-SPECIFIC SAMPLING FOR STUDIES OF DRILLING PREDATION: CONFIRMATION FROM FOUR BIVALVE SPECIES IN THE PLEISTOCENE OF NORTH CAROLINA

Taxon-specific (targeted) sampling has been considered biased compared to bulk sampling for drilling predation studies. Expanding on Ottens et al. (2010), we demonstrate that targeted sampling can yield results comparable to bulk sampling, and that collector expertise has negligible impact if proper training is administered. Targeted sampling was performed in the lower Waccamaw Fm (Lower Pleistocene) at Register Quarry near Old Dock, NC. Five replicate targeted samples were obtained by each of five trained novice and three veteran collectors for the bivalves Astarte concentrica, Cyclocardia granulata, and Lirophora latilirata. Drilling predation metrics for the samples were compared to determine if collector expertise affects study results and whether targeted and bulk sampling produce comparable results. Measurements included shell length and thickness; frequency of left valves and position and size of drillholes were also tallied. Drilling frequency, prey effectiveness, and size selectivity were calculated for each taxon replicate for all collectors. Results for novice collectors were compared to those for bulk samples and veteran collectors (999 tests). Nearly all significant differences in unstandardized data occurred in the size-related variables length and thickness. When data were size standardized, as in many drilling predation studies, only 3.3% of tests for statistical differences in collection methods for Astarte, Cyclocardia, and Lirophora were significant, and no tests for differences in novice and veteran sampling were significant. Glycymeris americana was also collected; preliminary analyses include data from Glycymeris in bulk samples and specimens collected by one novice and one veteran. Size range of Glycymeris is highly variable, so we hypothesized that results may differ from those for the other genera, especially for size-related variables. Initial results for Glycymeris are similar to those for the other taxa; most significant differences appeared in method comparisons using unstandardized data. Few comparisons involving standardized data or collector expertise yielded significant results. Future work will include data for Glycymeris collected by all novice and veteran collectors to further test the effects of shell size range on validity of targeted sampling.