DOES ABUNDANCE PROMOTE SURVIVORSHIP DURING BACKGROUND EXTINCTION INTERVALS? A CASE STUDY USING BIVALVE SPECIES FROM THE YORKTOWN FORMATION

Recent work suggests that abundance does not correlate with survivorship during mass extinction events; however, the link between abundance and survivorship during background intervals has yet to be tested. The purpose of this study is to quantify the correlation between survivorship, as measured via stratigraphic range, and abundance, in bivalve species from the Yorktown Formation (Pliocene). Three localities were sampled along the James River in southeastern Virginia. Stratigraphic sections were measured and described in terms of faunal content, lithology, and sedimentary structures. Thirty bulk samples were collected from the Sunken Meadow Member (Zone 1) of the Yorktown Formation. Samples were sieved through 2.80mm and 1mm sieves to remove sediment, and the fossil material was sorted and identified to the species level using literature descriptions. Raw abundance was compiled by counting individual valves. Rank and proportional abundance were derived from raw abundance. Species stratigraphic ranges were calculated from occurrence data available in the literature. The correlation between stratigraphic range and abundance was assessed via both parametric and non-parametric statistical analyses. Preliminary data derived from past studies show a complex relationship between survivorship and abundance. Data from different studies yield conflicting results; but overall no statistically significant relationship between abundance and survivorship was detected. These results conflict with the correlation observed between abundance and survivorship at ecological timescales; however, additional analysis is necessary before these results can be verified.