THE INCREASING INFLUENCE OF HUMANS ON MAMMALIAN MACROECOLOGICAL PATTERNS OVER THE LATE QUATERNARY

Starting in the middle to late Pleistocene, large-bodied mammals have been systematically extirpated from much of the Earth’s surface where they were once abundant. While all major continents once harbored giant mammals such as mammoth, woolly rhinoceros, mastodon, camels, llamas, and/or horses, few of these extremely large-bodied species remain, and they are mostly confined to the African continent. This decline mirrors the movement of modern humans across the globe and has intensified as human populations increased and expanded over the late Quaternary. Yet, the consequences of this prolonged loss of megafauna biodiversity have been understudied. Here, we quantify a number of important macroecological patterns of mammals over time to investigate how the loss of megafauna has influenced the shape and functioning of ancient and modern ecosystems and what modern ecosystems will likely look like in the future. Specifically, we focus on Africa, Eurasia and the Americas. Using a late Quaternary database (MOM v6.0) of mammals, we quantify the shape of the body size distribution, energy and biomass flow, and species diversity patterns at 6 time periods: 100ka, 20ka, 10ka, 0.3ka, modern and 0.2 ka years in the future. These time periods correspond to the dispersal of modern humans from Africa across the globe, before and after their entry into the Americas, European migration, and 200 years post modern. We assume that all mammals currently endangered become extinct. Our results show an increasing homogenization of ecosystems; although the continents experienced megafauna biodiversity losses of varying intensity at different times, future macroecologial patterns will be similar on each. Because megafauna have a disproportionate influence on ecosystem structure and function, ecological interactions between species, and even biogeochemical cycling, our results strongly suggest that continued ‘trophic downgrading’ may lead to unanticipated effects that influence virtually all aspects of ecosystems.