Quantifying the effects of climate change and human predation on the extinction of Late Pleistocene megafauna

Whether excessive hunting of Homo sapiens caused the extinction of Late Pleistocene megafauna or whether deglacial climate change was the main culprit has remained a controversial issue. Previous studies have focused on statistical relationships between human arrival time and megafauna disappearance, but so far no quantitative dynamical model has been presented that addresses this important issue. Here we introduce a new dynamical Lotka Volterra reaction diffusion partial differential equation model that explicitly simulates biomass variations of 2178 mammal species (including H. sapiens) across the globe, as well as predator/prey relationships and competition.  Key demographic parameters of this realistic model are estimated from allometric bodymass scaling relationships and the herbivore carrying capacity is obtained by combining habitat information and net primary information. The model simulates the patterns of key biological parameters, such as species richness, diversity, evenness and predator/prey relationships in close agreement to observational estimates. Changes in carrying capacity and climate parameters across the last glacial termination and into the Holocene have been estimated using the 3 million year transient paleo climate simulation conducted with the CESM1.2 earth system model at the IBS Center for Climate Physics. For Homo sapiens, the model also accounts for cultural carrying capacity. By turning on and off the human component during our transient simulations, we can determine the impact of agressive hunting on mammal populations and on megafauna in particular. Furthermore, by repeating these experiments for fixed climate time slices (Last Glacial Maximum, Mid Holocene), we can assess the climatic effect. Our model results demonstrate that 1) megafauna extinction was caused by excessive human predation, 2) in the absence of human hunting, there is no megafauna extinction, 3) deglacial climate change accelerates the overkill, because it increases the habitat suitability of humans in key areas of Eurasia.