A coupled climate-vegetation-mammal-human model for simulating Late Quaternary megafaunal extinctions

60，000 - 5，000年前，六大洲多达一千种大型脊椎动物（“巨型动物”）灭绝。了解这些故障的原因很重要，原因有几个。这是地质记录中最近的重大灭绝事件;有一个关于环境变化的详细知识的背景，以观察哺乳动物的反应;许多研究人员强烈暗示人类是部分或唯一的原因。出于所有这些原因，了解灭绝的原因，以及一些物种幸存而另一些物种没有幸存的原因，可以为解决当前的生物多样性危机提供独特的历史类比。巨型动物灭绝的两个主要竞争者是气候导致的植被变化和人类的狩猎，无论是单独还是组合。虽然灭绝是世界性的，我们将重点放在欧洲，北方亚洲和北美，因为这些地区有最好的数据分布和灭绝的哺乳动物。我们将首先在整个研究区域开发基于计算机的当地气候条件模拟;在过去的40，000年中，气候变化将首次逐年模拟。利用这些信息，我们将模拟整个地区的植被类型。当气候发生变化时，植被也发生了变化，但我们的模型比以前的模型更加现实，因为我们将考虑到植物物种在大面积上缓慢扩张时植被反应的滞后（例如，树木可能需要1500年才能到达北方欧洲，当时气候在长期寒冷之后变暖）。此外，该模型不仅估算了植被的类型，还估算了其生产力，即每年的生长量，这对食草哺乳动物至关重要。许多灭绝的哺乳动物（如长毛猛犸和长毛犀牛）都是适应末次冰期多产草原的食草动物，也是依赖它们生存的掠食者。许多幸存下来的是食草（林地）哺乳动物或混合栖息地。我们将为受害者和幸存者制定每个物种的生物学概况，包括体重，繁殖率和偏好的食物。这些将从活着的亲戚和直接证据中确定，例如化石牙齿的磨损表明饮食。我们亦会根据牠们过去所处的气候范围，确定牠们的气候耐受力，再把哺乳动物区系加入模拟的气候和植被中，然后用电脑模拟四万年前至今的气候变化，以及气候变化对每种哺乳动物的影响。此外，该模型将包括从哺乳动物的摄食活动到植被本身结构的反馈。模型中的最后一个元素是增加了人类狩猎的可变水平，人类的分布是从已知的考古遗址确定的。对所有数据的分析将确定气候和植被变化，加上或不加上狩猎，是否足以解释一些巨型动物的灭绝和其他动物的生存。这将通过将模型结果与基于化石记录的已知范围变化和灭绝模式进行比较来确定。我们开发的植被模型还可以预测对未来气候变化的可能反应。同样，气候模拟将适用于其他过程（例如北极永久冻土的变化程度）。我们的研究结果将直接与各利益相关者相关，为景观管理和生物多样性保护战略提供信息。我们将确保将这些建议传达给这些利益攸关方，以及科学界和更广泛的公众。

The period 60,000-5,000 years ago saw the extinction of up to a thousand species of large vertebrates ('megafauna') across six continents. Understanding the cause of these extinctions is important for several reasons. It is the most recent substantial extinction event in the geological record; there is a background of detailed knowledge about environmental change against which to view the responses of the mammals; and humans are strongly implicated by many researchers as partial or exclusive causal agents. For all of these reasons, understanding the cause of the extinctions, and the reasons why some species survived while others did not, can provide a unique historical analogue for addressing the current biodiversity crisis. The two main contenders for the megafaunal extinction are vegetation change driven by climate, and hunting by humans, either separately or in combination. Although the extinction was worldwide, we will focus on Europe, northern Asia and North America as these areas have the best data on the distributions and extinction of the mammals. We will first develop computer-based simulations of local climatic conditions across the study area; for the first time climate changes will be modelled on a year-by-year basis over the past 40,000 years. Using this information we will model vegetation types across the entire area. When climate changed, vegetation changed, but our model will be crucially more realistic than previous ones in that we will allow for the lags in vegetational response as plant species expand slowly across large areas (e.g. trees may have taken 1500 years to arrive in northern Europe when climate warmed after a long cold spell). In addition, the model estimates not only the type of vegetation but its productivity, i.e. amount of growth each year, of crucial importance to herbivorous mammals. Many of the mammals that went extinct (such as the woolly mammoth and wooly rhinoceros) were grazing species adapted to the productive grasslands of the last glaciation, and the predators that depended on them. Many of those that survived were browsing (woodland) mammals or those of mixed habitats. We will develop, for both victims and survivors, a biological profile for each species including their body weight, reproductive rate, and preferred foods. These will be determined from living relatives and from direct evidence such as wear on fossil teeth that indicates diet. We will also establish their climatic tolerance from the range of climates they occupied in the past.Adding the mammal fauna to the modelled climate and vegetation, and running the computer model from 40,000 years ago up to the present, the effect of climate changes on the vegetation, and the effect of both on each mammal species, will be evident. Moreover, the model will include feedback from the feeding activities of the mammals to the structure of the vegetation itself. A final element in the model is the addition of variable levels of human hunting, the distribution of people being determined from known archaeological sites. Analysis of all the data will determine if climatic and vegetational change, with or without the addition of hunting, are sufficient to account for the extinction of some megafauna and survival of others. This will be determined by comparing model results with the known pattern of range changes and extinction based on the fossil record. The vegetation model that we develop would also allow prediction of likely responses to future climatic changes. Similarly, the climate simulations will be applicable to other processes (e.g. the changing extent of arctic permafrost). Our results will be directly relevant to various stakeholders, informing landscape management and biodiversity conservation strategies. We will ensure that they are communicated to such stakeholders, as well as to the scientific community and wider public.