PREDATION AND COMMUNITY DYNAMICS IN THE PINECREST BEDS, TAMIAMI FORMATION, FLORIDA

Paleoecology provides an understanding of how Earth’s ecosystems have varied through time. Predation is one of the most important ecological variables, with potential to influence community structure and evolution. Understanding the ecological changes through a stratigraphic series of communities depends on the spatial heterogeneity within the stratigraphic units. Here, we examine how two temporally-equivalent assemblages from Unit 7 of the Tamiami Formation differ in terms of composition and drill hole frequency (DHF). This study is unique because it is one of the first to specialize on predation rates across all taxa in the Tamiami Formation.

Samples were collected from the Plio-Pleistocene Tamiami Formation at the SMR Aggregates Quarry in west Florida. Unit 7 is located in the lower Pinecrest Beds and is composed of mixed marine fossils. Two samples were collected 400 m apart, from the same stratigraphic bed. The samples were cleaned, identified to genus, and counted. Taxa found in our samples include bivalves, gastropods, barnacles, corals, and evidence of crabs, urchins, chitons, and shark teeth. We compared richness, evenness, Shannon Wiener index, and drill hole frequency between the two samples.

Sample 5 had a richness of 74, an evenness of 0.85, and a Shannon Wiener index of 3.66. Sample 10 had a richness of 75, an evenness of 0.83 and a Shannon Wiener index of 3.58. DHF in sample 5 was calculated at 2.6% for bivalves, 1.2% for gastropods, and 2.4% combined. In sample 10, the DHF was 5.8% for bivalves, 4.3% for gastropods, and 5.2% combined. These data indicate that the ecosystem was species-rich with similarities between evenness and diversity. Furthermore, DHF between bivalves and gastropods show that only a fraction of taxa were preyed upon. This lack of predation could be the cause of such a high richness and evenness for Unit 7. Although the DHF’s were low, they did differ between the two samples, indicating that predation rates vary due to spatial heterogeneity. We plan to examine 2 to 8 more samples from Unit 7 for additional data, along with the implementation of crushing repair scar data.