A niche-modelling approach to understanding late-Quaternary megafaunal extinctions

一些大型哺乳动物(‘巨型动物’)在最后一次冰川时期结束时或之后灭绝。它们灭绝的原因，特别是一些物种灭绝的原因，而同一地区其他大型哺乳动物存活到今天的原因，仍然是科学家们争论的问题。为了解释物种灭绝的原因，提出了两个主要假设。首先，人们认为，冰川阶段结束时的主要气候变化和相关的生态剧变导致物种适应的条件不再适用于它们。其次，鉴于灭绝与人口增长和人类地理范围扩大的巧合，有人认为，人类活动，主要是狩猎对大型动物种群施加的压力，造成了灭绝。我们建议采用一种新的方法来研究这些灭绝，并区分这些不同的解释。我们的研究将独特地结合：(I)直接从大型动物物种化石上获得的高质量放射性碳测年的详细年代信息；(Ii)使用与模拟未来潜在气候相同的气候模型模拟感兴趣时期的过去气候；以及(Iii)大型动物物种栖息地和饮食的证据。后者将从以下方面推断：(I)过去植被的模拟；(Ii)过去植被的记录；以及(Iii)发现与植物遗骸直接相关的大型动物物种化石的罕见情况，特别是在保存胃内容物的永久冻土化石的情况下。我们将使用这些数据来建立模型，将大型动物物种的地理范围与气候、栖息地和它们的食物组成联系起来。然后，我们将使用这些模型来模拟每个物种的变化潜力范围。这些模型和这些模拟将使我们能够评估一系列假设，对其进行检验是我们研究的主要目的。我们的研究将涵盖欧亚大陆北部和北美的所有地区，使我们能够包括过去横跨这两大洲的物种的完整地理范围，并将从大约50,000年前延伸到大约5,000年前。除了研究一系列已灭绝的物种，包括草食动物、肉食动物和杂食动物外，我们还将研究存活到今天的一系列可比较的物种。在这些情况下，我们还将使用记录物种当前地理分布的数据。通过研究灭绝和幸存的物种，我们将能够进行批判性的比较，从而洞察决定哪些物种存活下来，哪些物种灭绝的因素。我们的研究结果将有助于阐明环境变化，特别是气候变化，物种本身的生态特征，以及人类活动在导致物种灭绝方面的相对重要性。

A number of large mammals ('megafauna') became extinct towards, or following, the end of the last glacial period. The cause of their extinction, and in particular the reason why some species went extinct, whereas other large mammals survived to the present day in the same regions, remains a matter of debate amongst scientists. Two principal hypotheses have been advanced to account for the extinctions. Firstly, it is suggested that the major climatic changes and associated ecological upheavals of the end of the glacial stage resulted in the conditions to which the species were adapted no longer being available to them. Secondly, given the coincidence of the extinctions with an increasing population and expanding geographical range of humans, it is suggested that human activities, principally the pressures exerted upon the megafaunal populations by hunting, caused the extinctions. We propose to adopt a new approach to investigating these extinctions and to discriminating between these alternative explanations. Our research will uniquely combine: (i) detailed dating information from high quality radiocarbon dates made directly on fossils of megafaunal species (ii) simulations of past climate for the periods of interest made using the same kind of climate model as is used to simulate potential future climates; and (iii) evidence of megafaunal species' habitats and diets. The latter will be inferred from: (i) simulations of past vegetation; (ii) records of past vegetation; and (iii) those rare instances where fossils of megafaunal species are found directly associated with plant remains, notably in the case of fossils from the permafrost in which the stomach contents are preserved. We will use these data to construct models relating the megafaunal species' geographical ranges to climate, habitat and components of their diet. We will then use these models to simulate the changing potential range of each species. The models and these simulations will enable us to assess the series of hypotheses, testing of which is the principal aim of our study. Our study will encompass all of northern Eurasia and North America, enabling us to include the complete geographical ranges of species that ranged across both continents in the past, and will extend from about 50,000 years ago to about 5,000 years ago. In addition to studying a range of extinct species, including herbivores, carnivores and omnivores, we will also examine a comparable range of species that survive to the present day. In these cases we will also use data recording the species' current geographical distributions. By examining both extinct and surviving species we will be able to make critical comparisons that will provide insight into the factors determining which species survived and which suffered extinction. The results of our study will help elucidate the relative importance of environmental, especially climatic, change, of the ecological characteristics of the species themselves, and of human activities, in causing the extinctions.