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，气候变化在冰河时代和温暖的“间冰期”之间发生了快速波动。在冰河时代的高峰期，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。这些变化对岛屿的影响最大。许多岛屿特征与海平面有关-随着海平面下降，它们变得更大，更接近大陆（可能形成陆桥）;当海平面上升时，情况正好相反。我们从现代岛屿中了解到，岛屿越小，它们能支持的物种就越少。岛屿物种也往往是该岛屿特有的，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来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矮--这一现象随着在印度尼西亚弗洛雷斯岛上发现的侏儒化石而变得突出。在某些物种中，侏儒化是极端的（例如，西西里的大象体重为150公斤，而大陆祖先的体重为10，000公斤），我们将以此作为进化变化的“标记”。到目前为止，还没有人考虑过在气候变化的背景下侏儒哺乳动物的进化，因为几乎没有可靠的日期告诉我们这些物种是何时进化的。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的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，比较将使我们能够确定有多少种侏儒，以及他们的祖先。通过比较测量数据，我们可以计算出身体大小和重量的减少百分比，牙齿和骨骼的更详细特征将揭示这些侏儒是否特别适应岛屿环境。其次，我们将使用尖端技术来确定矮物种的地质年龄。我们将采用四种不同的测年方法，使我们能够在很小的误差范围内确定年龄。这些方法使用哺乳动物的牙齿遗骸，以及发现它们的沉积物中的贝壳和沉积物，还需要在现场进行测量。为此，我们将访问西西里、马耳他、克里特岛和塞浦路斯的一些关键地点，在那里发现了矮象的遗骸，并进行小型挖掘，以产生新的材料，用于测年和与以前挖掘的化石进行比较。第三，我们将利用关于过去百万年来气候和海平面变化的现有知识，绘制岛屿大小和形状变化的地图，并就西西里和马耳他而言，绘制它们相互之间以及与大陆之间可能的联系。把这三条线索放在一起，我们将能够确定全球变化如何影响哺乳动物的进化。重大的气候事件是否引发了许多岛屿的进化爆发？进化的速度是多少？矮种是存活了很长时间，还是很快就灭绝了，也许是由于进一步的气候变化？同样的事情是否以循环的方式反复发生？矮化的程度是否受岛屿大小、分离时间或其他因素（如可用植被）的影响？该项目的结果将提供全球变化对哺乳动物进化影响的缩影。这也将有助于解释一个长期争论的现象-岛屿矮化。最后，它将改进方法并产生更广泛应用的数据，特别是在地中海周围重要地质遗址的拟议定年方面。

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.