Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions

Abstract

The late Quaternary period saw the rapid extinction of the majority of the world's terrestrial megafauna. The cause of these dramatic losses, especially the relative importance of climatic change and the impacts of newly arrived people, remains highly controversial, with geographically restricted analyses generating conflicting conclusions. By analyzing the distribution and timing of all megafaunal extinctions in relation to climatic variables and human arrival on five landmasses, we demonstrate that the observed pattern of extinctions is best explained by models that combine both human arrival and climatic variables. Our conclusions are robust to uncertainties in climate data and in the dates of megafaunal extinctions and human arrival on different landmasses, and strongly suggest that these extinctions were driven by both anthropogenic and climatic factors.M ost of the terrestrial megafauna present 100,000 years (100 ky) ago are now extinct (1). The extinctions were geologically rapid, and almost all occurred in the past 50 ky, but their exact timing varied among different parts of the world (2). Climatic change, and overhunting, habitat alteration, or the introduction of a novel disease by recently arrived people have been put forward as competing, and sometimes interacting, explanations (3). In addition to its enormous paleontological significance, this debate has drawn wide interest for its relevance to the relationship of humans with nature and to our understanding of the current anthropogenic extinction episode (4-8).Attempts to explain megafaunal extinctions have, in addition to examining the effect of factors such as size and reproductive rate on extinction probability (9, 10), often focused on matching them in space and time with either climatic change or human arrival (11-13). However, most studies have been limited to single regions and limited numbers of taxa (e.g., 14-18), and have been beset by uncertainties in the accurate dating of human and/or megafaunal remains [e.g., the Cuddie Springs site in Australia (19-21)]. We believe that the problem is better approached by considering several landmasses simultaneously and dealing explicitly with uncertainty.We did this by analyzing the relationship, across different areas and time periods, between variation in extinction rate and variations in human arrival and climatic conditions. Specifically, we compiled a dataset of human arrival (Table 1) and megafaunal extinction dates (Table S1) from the literature. We used the Antarctic Dome C core (22) as our main source of information on climatic variability; this dataset is the most complete among available time series and is well correlated with other time series at the scale used for our analysis (Tables S2-S4). We used generalized linear models (GLMs) with a binomial error structure and a logit link function to explore the role of human arrival (classified as either just arrived or not) and climatic variables in predicting the probability of extinction for a given landmass and time period (quantified as ...

Human arrival scenarios have a strong influence on interpretations of the late Quaternary extinctions

“…1). Nevertheless, we consider that some of the scenarios for each landmass used by Prescott et al (1) are considerably less plausible than others (Table 1). For instance, human arrivals in North and South America between 30 and 20 kya (2) and less than 10 kya (3), respectively, and in Australia between 30 and 20 kya (4), are less strongly supported in the literature than alternative dates (Table 1), but Prescott et al (1) assumed all scenarios to be equally plausible.…”

“…However, the analyses of Prescott et al (1) are based on coarse temporal resolution and alternative scenarios describing the earliest human arrival on five landmasses, which incorporate uncertainties from the literature (table S5 in ref. 1).…”

“…The study by Prescott et al (1) provides an inspiring quantitative framework for disentangling the effects of humans and climate on megafaunal extinctions, which is essential because their relative importance across time and space remains one of the key missing pieces for solving the late Quaternary extinctions puzzle. However, the analyses of Prescott et al (1) are based on coarse temporal resolution and alternative scenarios describing the earliest human arrival on five landmasses, which incorporate uncertainties from the literature (table S5 in ref.…”

Climate, not Aboriginal landscape burning, controlled the historical demography and distribution of fire-sensitive conifer populations across Australia

“…Indeed, burning is postulated as the key driver of the mass extinction of megafauna in Australia around 45-50 kya through altering vegetation to fire-adapted plant communities [8]. On the other hand, there is a lack of congruence between human activity and fire records during 20-40 kya, a period of consistently low Aboriginal populations [9] and large changes in fire regimes [10], and recent studies argue for significant roles of climate change on vegetation shift and megafauna extinction [11][12][13][14]. Furthermore, studies of sedimentary records from the humid tropics and southeastern Australia suggest an ecological feedback, where relaxed herbivore pressure following extinction of megaherbivores resulted in a switch to flammable sclerophyllous vegetation, which increased fire activity [15,16].…”

Reply to Brook et al: No empirical evidence for human overkill of megafauna in Sahul

“…The most parsimonious interpretation of these data is that the extinction process unfolded over multiple glacial cycles, with most now-extinct taxa gone before human arrival and subsequent extinctions occurring against a backdrop of significant climate change. Our climate-based argument is not dependent on each of the most recent glacial-interglacial cycles being more extreme or that the last was necessarily the most severe, although support grows for this contention (3,6).…”