WAS IT WORTH IT? EFFECT OF INCREASING SAMPLE SIZE AND EFFORT WHEN ANALYZING THE PALEOECOLOGY OF A PLIO-PLEISTOCENE MOLLUSC ASSEMBLAGE FROM FLORIDA

Two bulk samples from the Caloosahatchee Fm were analyzed by three paleontology classes and as independent study projects over a 10-year period at University of North Carolina Wilmington. Samples were collected 3.5 km west of La Belle, FL, by Squires and Heaslip in 1955 and housed at the American Museum of Natural History; they likely also contain Bermont Fm material, which had not been differentiated at time of collection. Comparison of results obtained by successive sets of students permits analysis of the effect of increasing effort on paleoecological analysis, including diversity and drilling predation metrics.

We identified >30,000 mollusc specimens >5mm to species level when possible during the past decade. Classes in 2006, 2008, 2014, and independent studies in 2015 and 2016 increased sample size of identified bivalves from 3809 to 27149 and of identified gastropods from 1499 to 3271. With increased effort, recorded richness increased from 39 to 59 bivalve species and from 26 to 59 gastropod species. Early work focused on large, distinctive taxa and avoided small, hard-to-identify species. When smaller taxa were added, dominance and evenness changed significantly. Bivalve richness increased most markedly between the 2008 and 2014 classes due to the identification of small bivalves, including ~17,000 Transennella; consequently dominance increased significantly from 0.395 to 0.442 and evenness dropped significantly from 0.133 to 0.071. Post-2014 independent studies concentrated on gastropods and significantly decreased dominance (from 0.18 to 0.15) and evenness (from 0.36 to 0.20) when small, rare, hard-to-identify snails were added to the database.

Predatory drillholes were tallied and drilling frequency (DF) and prey effectiveness (PE = frequency of incomplete drillholes) were calculated for each species and the bivalve and gastropod assemblages. Assemblage DF changed with increasing effort (from 0.08 to 0.05 for bivalves and 0.005 to 0.05 for gastropods) with significant differences between 2008 and 2014, when smaller taxa were added. PE increased from 0.007 to 0.10 for bivalves and from 0 to 0.20 for gastropods with increased effort and data collection by more experienced students. Increased effort yielded more accurate representation of the community primarily due to inclusion of smaller taxa.