DOES SPATIAL HETEROGENEITY AFFECT PREDATION WITHIN THE PINECREST BEDS, TAMIAMI FORMATION, FLORIDA?

Predation can influence community structure and evolutionary trends, so understanding predation in prehistoric environments gives crucial insight into environmental conditions of the past. Here, we compare predation in six temporally-equivalent assemblages from the Plio-Pleistocene Tamiami Formation, Florida to see if a single sample can accurately describe predation and community composition for the entire bed.

Samples were collected from Unit 7 (lower Pinecrest Beds) of the marine Tamiami Fm at SMR Aggregates. Six samples were collected 100 – 200 m apart, south to north, from one stratigraphic bed. After processing the samples, we compared generic richness, evenness, drillhole frequency (DHF) and repair scar frequency (RF) among gastropods and bivalves. We used two-value P-tests of difference to compare predation frequencies between samples.

Richness ranged from 35 to 79 and evenness from 0.72 and 0.84. Predation trace frequencies were low. For all mollusks, DHF ranged from 2.5% to 11.3% and RF from 3.2% to 6.5%. Sample 3 had the lowest DHF for bivalves (3.3%). Sample 1 had the lowest DHF and RF for gastropods (0%). Sample 2 had the lowest RF for epifaunal bivalves (0%) but had the highest DHF for bivalves (12.6%; infaunal bivalves 13.8%) and gastropods (7.4%). Sample 1 had the highest RF for bivalves (8.2%). Sample 2 had the highest RF for gastropods (10.6%).

Sample 1 had the highest overall repair frequency (6.5%), as well as the highest RF for epifaunal bivalves (15.7%). In addition, it had the lowest richness among the samples (35 genera compared to an average of 65). This suggests that this southernmost sample had a different community make-up than the other five samples. There was at least one significant (p < 0.05) comparison for each sample, with the greatest number for sample 3. Possible causes for the variation include preferences for certain prey taxa, alternate predation methods (e.g., suffocation), or competition (crabs and sharks occurred in the samples). Due to the spatial variation in predation and community composition, a single sample is not viable to describe an entire community. For more accurate data, we suggest collecting multiple lateral samples when examining communities and predation through time.