People, not the climate, caused the decline of the giant mammals

Probably should link the paper that just came out about this https://www.sciencedirect.com/science/article/pii/S221330542300036X > Highlights > > • > Modern humans (Homo sapiens) drive late-Quaternary megafauna extinctions, with no role for climate change. > > • > The strong body-size bias of the late-Quaternary extinctions is also linked to modern humans, not climatic change. > > • > The late-Quaternary extinctions represent the first planet-wide, human-driven transformation of the environment. > > The results presented here did not provide support for an extinction event driven primarily by climate change or by climate change-human pressure interactions. Precipitation was consistently unable to predict extinction severity or bias with any accuracy, while the moderate predictive ability of temperature corresponds to the overlap of countries with the greatest climatic change/variability and those where modern humans were the most novel in the landscape. The existence of regions where climate change was comparatively moderate and where there was, nonetheless, very high extinction severity such as in South America shows that human activity is the necessary factor. > > The severity and impact of megafauna extinctions is best explained by Homo sapiens migration history > > These models show that human migration can predict the local severity of late-Quaternary extinctions far more effectively than climate change, with **no support for an extinction driven primarily or even secondarily by climate**. While the results of the model based on Homo distribution support the hypothesis that areas with longer hominin occupation experienced lower extinction rates due to longer periods of co-adaptation, higher correlations were obtained by using a model based only on the migration of H. sapiens. > > It might also be that species traits associated with vulnerability to hunting, such as reproductive turnover or mobility, were not uniformly distributed, e.g. large numbers of slow-moving, large-bodied ground sloths (≥19 non-insular species) and giant armadillos (≥12 species) in the Americas > > These results support the conclusion that Homo sapiens not only had a catastrophic impact on megafauna diversity, but also on the distribution of body mass amongst global megafauna communities, with the greatest portion of megafauna biomass removed in areas where humans arrived most recently. In some cases, the result was the eradication or near-eradication of megafauna from entire continents, and even in regions that experienced low total severity it was the largest species that disappeared. This has major implications for the current functionality of ecosystems in areas where humans had the greatest impact. > > this would suggest that not only does the history of human-led extinction go back far earlier than conventionally accepted, but so does the history of anthropic environmental impact, with strong geographic differences in its severity linked to human biogeography. While the extinction of numerous megafauna species would strongly affect ecosystem and biosphere functioning regardless of cause, attribution to modern humans puts these extinctions in the same context as that of ongoing extirpations and extinctions. > > This extreme, human-linked downgrading of the Earth’s fauna, unique in the Cenozoic record (Smith et al., 2018), has resulted in the widespread formation of ecosystems with simplified and degraded large animal faunas. Because such “small” faunal assemblages are without analog across the last 30 + million years (Smith et al., 2018), these ecosystems can be considered novel, i.e., human-caused and self-maintaining with unprecedented composition or function > > Hence, given the ecological importance of large-bodied animals (e.g. Enquist et al., 2020), this global downgrading of faunas represents the **first planetary-scale human-driven environmental transformation**. > > While Pleistocene is defined by glacial cycles and now the Anthropocene by global human impact on geological and meteorological systems, the defining element of the Holocene seems to be the global occurrence of Homo sapiens, and the linked, near-complete erosion of megafauna communities worldwide. > > Integrating novel data on late-Quaternary large mammals, covering 158 extinct and 329 extant species, and climate change over the past 120,000 years, this study > > 1) strongly supports Homo sapiens as responsible for the megafauna extinctions during the late-Quaternary and > > 2) for the size-bias in the extinctions and associated loss in ecological functioning that has occurred during that time, with little to no influence by climate change, firmly answering both of our research questions. > > These findings extend the period of planetary scale human impacts on the environment back into the Late Pleistocene or possibly even earlier.