INTER-HEMISPHERIC COMPARISON OF THE PLIO-PLEISTOCENE EXTINCTION EVENT (PPEE): LINKING THE ENERGY USE AND FUNCTIONAL DIVERSITY

PPEE is the penultimate global biodiversity crisis associated with drastic changes in ocean circulation patterns and marine productivity. However, the consequences of the PPEE across hemispheres remained unexplored. We evaluate how the energy use and guild structure of North (Florida) and South American (Chile) gastropod species assemblages are modulated by PPEE bottom-up effects. Diversity parameters and gastropod body size were estimated through bulk sampling across the PPEE boundary in Florida sections that span the upper Pliocene and the lower Pleistocene (Sarasota, Florida). Chilean data combined the literature data and samples taken from fossiliferous sites spanning the Pliocene and Pleistocene of the northern Chile. Biovolume for each species was estimated from morphometric measurements. Rarefaction techniques and Jaccard index were used to estimate taxic richness and faunal turnover throughout the PPEE interval. Species biomass and energy use were estimated from biovolume using allometric equations. Population energy use was estimated as the product of species abundance and species energy use. Finally, each gastropods species was categorized according to their lifestyle following the ecospace model, and Functional richness (FR), dispersion (FD) and redundancy (FRed) were estimated. Both the Chilean and the Florida assemblages recorded high compositional changes across the PPEE. After the extinction event, Florida assemblages displayed reduction in body size, decreased abundance, suppressed richness and decline in energy use, while Chile assemblages exhibited the opposite trends. In functional terms, Chilean assemblages did not show changes in FR, but FRed and FD were significantly higher for Pleistocene assemblages. In contrast, all functional parameters from the Florida assemblages decreased >70%. We suggest that the final closure of the Panama Seaway and the likely strengthening of the Humboldt current increased the upwelling regime and consequently enhanced the ocean productivity along the Chilean coast. Conversely, this event affected negatively the biodiversity at the Florida coast decreasing regional productivity. Our data suggest a bottom-up control via productivity as determinant of the level of energy use and functional organization of these assemblages during the PPEE.