Biotic responses to environmental change: dwarf mammals of Mediterranean islands as evolutionary experiments in the Quaternary

在过去的一百万年里，气候变化在冰期和变暖的“间冰期”之间迅速波动。在冰河时期的最高峰，海平面可能比现在低120米；然后，当气候变暖时，海平面会再次上升。了解这些变化的影响与了解当前全球变暖趋势的可能后果直接相关。这种变化对岛屿的影响最为强烈。许多岛屿特征与海平面有关——当海平面下降时，它们变得更大，更靠近大陆（可能形成大陆桥）；当水平上升时，情况正好相反。我们从现代岛屿上知道，它们越小，它们能养活的物种就越少。岛上的物种往往是岛上独有的，它们很容易灭绝。因此，岛屿物种形成了应对气候变化的“前线”。我们将调查过去一百万年气候变化对地中海岛屿大象和鹿的影响。他们最常见的进化反应是变成侏儒——这一现象随着在印度尼西亚弗洛雷斯岛发现的侏儒化石而变得突出。在一些物种中，侏儒化是极端的（例如，西西里岛上的大象体重为150公斤，而大陆上的大象祖先体重为10,000公斤），我们将把这作为进化变化的“标志”。到目前为止，还没有人考虑过侏儒哺乳动物在气候变化背景下的进化，因为几乎没有可靠的日期告诉我们这些物种是什么时候进化的。为了回答这些问题，我们将首先对博物馆中保存的矮鹿和大象化石进行详细的检查和测量。我们已经有了大陆物种的类似数据，通过比较，我们可以确定有多少种侏儒，以及它们的祖先。测量结果的比较将使我们能够计算出体型和体重减少的百分比，而牙齿和骨骼的更详细特征将揭示这些矮人是否已经特别适应了岛上的环境。其次，我们将使用尖端技术来确定侏儒物种的地质年龄。我们将采用四种不同的测年方法，它们之间的差异将使我们能够在很小的误差范围内确定年龄。这些方法使用的是哺乳动物的牙齿残骸，以及它们被发现的地方的贝壳和沉积物，还需要在现场进行测量。为此，我们将访问西西里岛、马耳他、克里特岛和塞浦路斯等发现侏儒象遗骸的重要地点，并进行小型发掘，为确定年代和与先前发掘的化石进行比较提供新的材料。第三，我们将利用现有的关于过去百万年气候和海平面变化的知识，绘制岛屿大小和形状变化的地图，并以西西里岛和马耳他岛为例，绘制它们彼此之间以及与大陆之间可能存在的联系。把这三条线索结合起来，我们就能确定全球变化是如何影响哺乳动物的进化的。是重大气候事件引发了许多岛屿上的进化爆发吗？进化的速度是多少？矮种存在了很长一段时间，还是很快就灭绝了，也许是由于进一步的气候变化？同样的事情会以循环的方式反复发生吗？矮化程度是否受到岛屿大小、分离时间或其他因素（如可用植被）的影响？该项目的结果将为全球变化对哺乳动物进化的影响提供一个缩影。这也将有助于解释一个长期争论的现象——岛屿侏儒现象。最后，它将改进方法并产生更广泛应用的数据，特别是在拟议的地中海周围重要地质遗址的年代测定中。

Climate change over the last million years has seen rapid fluctuations between ice ages and warmer 'interglacials'. At the height of an ice age the sea level could be up to 120 metres lower than it is today; then, when the climate warmed, the sea would rise once more. Understanding the impact of these changes has direct relevance to understanding the possible ramifications of the current global warming trend. The impact of such changes was felt most strongly on islands. Many island features are linked with sea level - they become larger and closer to the mainland (maybe forming a landbridge) as sea level drops; the opposite happens when levels rise. We know from modern islands that the smaller they are, the fewer species they can support. Island species are also often unique to that island, and they are vulnerable to extinction. Consequently, island species form a 'front-line' of response to climate change. We will investigate the effects of climate change over the last million years on island elephants and deer in the Mediterranean. Their commonest evolutionary response was to become dwarfed - a phenomenon that came to prominence with the discovery of a fossil dwarfed human on the island of Flores in Indonesia. In some species, dwarfing was extreme (elephants on Sicily, for example, weighed 150 kg, compared to a mainland ancestor of 10,000 kg), and we will use this as a 'marker' for evolutionary change. Until now, no one has considered the evolution of dwarf mammals in the context of climate change, because there are few reliable dates to tell us when these species evolved. To answer these questions we will first conduct detailed examination and measurement of fossils of the dwarf deer and elephants preserved in museums. We already have similar data on mainland species, and the comparison will allow us to determine how many species of dwarfs there were, and their ancestry. Comparison of measurements will then allow us to calculate the percentage reduction in body size and weight, and more detailed features of the teeth and bones will reveal whether the dwarfs had become specially adapted to the island environments. Secondly, we will use cutting-edge techniques to determine the geological age of the dwarf species. We will employ four different methods of dating that between them will allow us to determine ages within a narrow range of error. These methods use tooth remains of the mammals, and shells and sediments from the deposits in which they were found, and also require measurements to be taken at the sites. To this end we will visit a number of key localities on Sicily, Malta, Crete and Cyprus where remains of dwarf elephants have been found, and conduct small excavations to produce fresh material for dating and for comparison with previously-excavated fossils. Thirdly, we will use existing knowledge about climate and sea-level changes over the past million years to plot maps of the changing size and shape of the islands and, in the case of Sicily and Malta, their possible connections to each other and to the mainland. Putting together these three strands, we will be able to determine how global changes impacted the evolution of the mammals. Did major climatic events trigger bursts of evolution on many islands? What was the speed of evolutionary change? Did the dwarf species endure for a long time, or did they soon become extinct, perhaps due to further climate change? Did the same thing happen repeatedly in a cyclic fashion? Was the degree of dwarfing influenced by island size, time of separation, or other factors such as available vegetation? The results of this project will provide a microcosm of the impact of global change on mammal evolution. It will also help explain a long-debated phenomenon - that of island dwarfing. It will, finally, refine methods and produce data of broader application, especially in the proposed dating of important geological sites around the Mediterranean.