The Dynamics of Diachronous Extinction Associated with Climatic Deterioration near the Neogene/Quaternary Boundary

Abstract

To predict extinction we must understand the processes leading to terminal population decline. Once a critical threshold of population size is reached, small environmental perturbations can push a species over the cliff-edge to extinction, so the main drivers of extinction are the factors that cause the initial reduction in population size. Most studies of population decline leading up to extinction focus on modern species in a human-dominated world. The drivers of population decline leading to non-human mediated extinctions are less well known but changes in climate are arguably the most widely invoked mechanism. Here, we report data on >16,000 individuals of the planktonic foraminifer Globoconella puncticulata from six sites in the Atlantic Ocean along a 83 degree-long latitudinal transect, over a 600,000-year interval leading up to the species’ global extinction during the late Pliocene-earliest Pleistocene intensification of Northern Hemisphere glaciation. We show changes in geographic range, abundance and body size. We find that populations do not follow a North-to-South sequence in extinction as Earth cooled and developed large ice sheets in the high latitudes of the Northern Hemisphere. Instead, our results suggest that (1) populations are differentially adapted to local environmental conditions such as nutrient availability, (2) population dynamics in core populations differ from those at the edge of their range, and (3) individual population responses to external pressures are essential to understanding the drivers of global extinction. Our study demonstrates the potential to transform our understanding of extinction dynamics through spatially replicated sampling of the highly-resolved marine microfossil record.