Pleistocene Disruption of Trait-Environment Relationships Informs the Future Conservation of African Megafauna

Abstract

Mammalian megafauna have been critical to the functioning of Earth’s biosphere for millions of years. However, since the Plio-Pleistocene, their biodiversity has declined, concurrent with dramatic environmental change and hominin evolution. While these biodiversity declines are well-documented, their impacts on the ecological function of megafaunal communities remain uncertain. Here, we adapt ecometric methods to evaluate whether biodiversity losses since 7.5 Ma were coincident with disruptions to the functional link between communities of herbivorous, eastern African megafauna and their environments (i.e., functional trait-environment relationships). Herbivore taxonomic and functional diversity began to decline during the Pliocene, as open grassland habitats emerged, persisted, and expanded. In the mid-Pleistocene, grassland expansion intensified and Acheulean hominin tools emerged. It was then that phylogenetic diversity declined and the trait-environment relationships of herbivore communities shifted significantly. Our results divulge the varying implications of different losses in megafaunal biodiversity. Only the losses that occurred since the environmental and anthropogenic changes of the Pleistocene were coincident with a disturbance to community ecological function. Such a disturbance may occur in even greater magnitude in the future, as climate change and human impacts intensify. Preventing it will require that species move across landscapes, so that their traits may track changing environmental conditions. We build an ecometric model of modern megafaunal communities in Africa, and we use it to identify communities whose species will need to shift across space so that trait-environment relationships remain undisturbed. Conservation efforts that focus on movement routes between these communities will be critical if megafauna are to persist and continue providing essential ecological functions.