METABOLIC RATES, BODY SIZE, AND SPECIES TURNOVER DURING THE PLIO-PLEISTOCENE EXTINCTION EVENT

There is growing paleontological evidence that extinction selectivity cannot be explored reliably unless species energy use is considered explicitly. Specifically, an integration of body size [BS] data, richness estimates, and metabolic rate [MR] proxies is needed to assess whether species turnover across extinction events is influenced by energy use and nutrient flow. In this preliminary analysis, we examine the influence of BS, MR, and productivity on species turnover within two guilds of bivalve mollusks that persisted across the Plio-Pleistocene Extinction Event [PPEE]. The data collected thus far include anteroposterior measurements for 2,497 bivalve specimens that represent 63 species from two families (Pectinidae and Veneridae). The specimens were obtained from FLMNH collections spanning Pinecrest beds (Pliocene-Pleistocene), Caloosahatchee Fm. (early Pleistocene), and Bermont Fm. (middle Pleistocene). For each formation and family, kernel density estimation was used to quantify the modality of the BS distributions. Mean MR per species was estimated following the model of metabolic theory of ecology, which scales BS with ambient temperature at which metabolism occurs (warm temperate, range: 17-23°C, =20°C). Proxies of paleotemperature and nutrients data were obtained from literature. Logistic regressions were performed to relate extinction selectivity with the BS, MR, and nutrient variables. In addition, beta turnover rates in faunal composition were estimated using Jaccard similarity measure. On average, pectinids recorded larger BS and higher MRs through the extinction event (mainly, Caloosahatchee Fm.). Also, pectinids experienced higher turnover rates and more drastic post-extinction reduction in size relative to veneroids. Logistic regression indicated that nutrient concentration had a significant effect on species extinction, especially in pectinids. Finally, after the PPEE, both veneroid and pectinids were characterized by smaller BS and lower MR than their pre-extinction counterparts. The PPEE is believed to be characterized by a decline in nutrient supply. The preferential survival of small-bodied species with lower MR observed here supports the hypothesis that changes in nutrient supply played an important role during the PPEE.