Fifty millennia of catastrophic extinctions after human contact

104

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 ...

Section: Resultsmentioning

confidence: 59%

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

Prescott

Williams

Balmford

et al. 2012

104

“…Simplification of food webs and diversity loss are also evident in terrestrial records over the last 50 ka, usually with human involvement and entailing high extinction intensities (29,(126)(127)(128). Significant mammal and bird extinctions started with human expansion out of Africa in the Late Pleistocene, making initial contact with independently evolved faunas and eventually reaching Pacific islands by a few thousand years ago [approximately half of all mammal species >50 kg lost by ∼11 ka) (128); loss of ∼1,000 Pacific nonpasserine landbirds alone via preIndustrial hunting, habitat change, and species introductions (129)].…”

Section: Proxy Evidence Of (Paleo)environmentalmentioning

confidence: 99%

Biology in the Anthropocene: Challenges and insights from young fossil records

Kidwell

2015

127

With overwhelming evidence of change in habitats, biologists today must assume that few, if any, study areas are natural and that biological variability is superimposed on trends rather than stationary means. Paleobiological data from the youngest sedimentary record, including death assemblages actively accumulating on modern land surfaces and seabeds, provide unique information on the status of present-day species, communities, and biomes over the last few decades to millennia and on their responses to natural and anthropogenic environmental change. Key advances have established the accuracy and resolving power of paleobiological information derived from naturally preserved remains and of proxy evidence for environmental conditions and sample age so that fossil data can both implicate and exonerate human stressors as the drivers of biotic change and permit the effects of multiple stressors to be disentangled. Legacy effects from Industrial and even pre-Industrial anthropogenic extirpations, introductions, (de)nutrification, and habitat conversion commonly emerge as the primary factors underlying the present-day status of populations and communities; within the last 2 million years, climate change has rarely been sufficient to drive major extinction pulses absent other human pressures, which are now manifold. Young fossil records also provide rigorous access to the baseline composition and dynamics of modern-day biota under pre-Industrial conditions, where insights include the millennial-scale persistence of community structures, the dominant role of physical environmental conditions rather than biotic interactions in determining community composition and disassembly, and the existence of naturally alternating states.biodiversity | ecology | conservation | paleobiology | paleoecology

“…The woolly mammoth and horse disappeared during this event (1). The underlying cause of these extinctions has been the subject of a lengthy but unresolved debate, with proposed mechanisms including rapid overkill (''blitzkrieg'') by human hunters, changes in climate and vegetation, or a combination of these (2)(3)(4). Others have suggested that hyperdisease (5) or an extraterrestrial impact 12,900 Ϯ 100 years before present (yr BP)* (6, 7) were contributory factors.…”

mentioning

confidence: 99%

Ancient DNA reveals late survival of mammoth and horse in interior Alaska

Haile

Froese

MacPhee

et al. 2009

247

181

Causes of late Quaternary extinctions of large mammals (''megafauna'') continue to be debated, especially for continental losses, because spatial and temporal patterns of extinction are poorly known. Accurate latest appearance dates (LADs) for such taxa are critical for interpreting the process of extinction. The extinction of woolly mammoth and horse in northwestern North America is currently placed at 15,000 -13,000 calendar years before present (yr BP), based on LADs from dating surveys of macrofossils (bones and teeth). Advantages of using macrofossils to estimate when a species became extinct are offset, however, by the improbability of finding and dating the remains of the last-surviving members of populations that were restricted in numbers or confined to refugia. Here we report an alternative approach to detect 'ghost ranges' of dwindling populations, based on recovery of ancient DNA from perennially frozen and securely dated sediments (sedaDNA). In such contexts, sedaDNA can reveal the molecular presence of species that appear absent in the macrofossil record. We show that woolly mammoth and horse persisted in interior Alaska until at least 10,500 yr BP, several thousands of years later than indicated from macrofossil surveys. These results contradict claims that Holocene survival of mammoths in Beringia was restricted to ecologically isolated high-latitude islands. More importantly, our finding that mammoth and horse overlapped with humans for several millennia in the region where people initially entered the Americas challenges theories that megafaunal extinction occurred within centuries of human arrival or were due to an extraterrestrial impact in the late Pleistocene.extinction ͉ permafrost ͉ megafauna ͉ Beringia