ANALYSIS OF MOLLUSK TROPHIC GUILDS THROUGHOUT THE PLIO-PLEISTOCENE OF FLORIDA: ECOLOGICAL CONSEQUENCES OF FAUNAL TURNOVER

For this study, bulk samples from localities representing Florida's Plio-Pleistocene strata were analyzed to determine the stratigraphic patterns of mollusk trophic guilds through this interval of documented faunal turnover. Samples were collected from the Pliocene Pinecrest beds at SMR Aggregates, Late Pliocene Caloosahatchee at Piper Rd., Early Pleistocene Bermont at Longan Lakes Quarry, and Late Pleistocene Ft. Thompson at Caloosa Shell and Quality Materials sites. Bulk samples from each site were washed using sieves with 3 and 5.5 mm mesh sizes, but only the >5.5 mm specimens were used. These were divided into carnivore, herbivore and suspension feeder groups. By studying the temporal and spatial changes in the nature of feeding we are provided with better insight on the evolutionary patterns of feeding types and ecological consequences prior to and following an interval of faunal turnover.

The SMR-8 Pinecrest samples showed a carnivore-dominated assemblage stratigraphically lower in the unit but with an increasing dominance of suspension feeding taxa up section. The suspension feeders comprised 49% (n=909) of the SMR samples, the carnivores 46%. The Caloosahatchee Piper Pit sample was carnivore dominated with 44% (n=1204) with suspension feeders at 35%. A drastic change is visible in the Bermont Longan Lakes samples with both carnivores and suspension feeders greatly decreasing and herbivores dominating 57% (n=6144) the assemblage. The Caloosahatchee-Bermont boundary has traditionally been identified as the approximate time of most intense extinction. The late Pleistocene Ft. Thompson localities show an increase in percentages of carnivores, further than that of the pre-extinction Pinecrest, with 75% (n=125) carnivores in the Caloosa Shell samples and 83% (n=144) in the QM samples, with the suspension feeders decreasing further in QM to 3% of the assemblage. This is not evidence of ecological recovery, however, as all gastropods became exceedingly rare relative to bivalves after the Bermont.