Island-wide aridity did not trigger recent megafaunal extinctions in Madagascar
Island-wide aridity did not trigger recent megafaunal extinctions in Madagascar
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DOI：
10.1111/ecog.02376
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发表时间：
2017-08-01
期刊：
影响因子：
5.9
通讯作者：
Burney, David A.
中科院分区：
文献类型：
--
作者：
Crowley, Brooke E.;Godfrey, Laurie R.;Burney, David A.
研究人员对人类与气候在触发马达加斯加岛上特有的大型动物群的晚全新世灭绝方面的相对重要性存在分歧。具体来说，一个戏剧性的和同步的减少乔木花粉和增加草花粉约1000年前已被交替解释为干旱化的证据，增加人类活动，或两者兼而有之。由于干旱化和人为砍伐森林对植被的影响类似，因此解决这些因素中的哪一个（如果有的话）导致马达加斯加巨型动物的灭绝仍然是一个挑战。我们使用稳定的氮同位素（δ N-15）值从放射性碳定年亚化石脊椎动物解开自然和人为引起的变化的相对重要性。如果增加的干旱是负责巨型动物的下降，那么我们预计在整个岛屿的三角洲N-15值的增加达到最高值的时候，建议最大的干旱在约1000年前。或者，如果气候相对稳定，人为栖息地的改变解释了孢粉学信号，那么我们可以预期栖息地湿度几乎没有变化，并且随着时间的推移，三角洲N-15值没有系统的方向性变化。在考虑了饮食、地理区域和沿海邻近性的混杂影响后，我们发现在过去的10 000年里，三角洲N-15值没有变化，也没有支持一个显著的、地理上广泛的干旱化时期，该时期在900-950年前达到顶峰。相反，大约在那个时候草的增加可能标志着人类土地使用向更专注的农牧生活方式的转变，而当时巨型动物种群已经在下降。大约1000年前的土地使用变化只会加速马达加斯加巨型动物的不可避免的消失。
Researchers are divided about the relative importance of people versus climate in triggering the Late Holocene extinctions of the endemic large-bodied fauna on the island of Madagascar. Specifically, a dramatic and synchronous decline in arboreal pollen and increase in grass pollen ca 1000 yr ago has been alternatively interpreted as evidence for aridification, increased human activity, or both. As aridification and anthropogenic deforestation can have similar effects on vegetation, resolving which of these factors (if either) led to the demise of the megafauna on Madagascar has remained a challenge. We use stable nitrogen isotope (delta N-15) values from radiocarbon-dated subfossil vertebrates to disentangle the relative importance of natural and human-induced changes. If increasing aridity were responsible for megafaunal decline, then we would expect an island-wide increase in delta N-15 values culminating in the highest values at the time of proposed maximum drought at ca 1000 yr ago. Alternatively, if climate were relatively stable and anthropogenic habitat alteration explains the palynological signal, then we would anticipate little or no change in habitat moisture, and no systematic, directional change in delta N-15 values over time. After accounting for the confounding influences of diet, geographic region, and coastal proximity, we find no change in delta N-15 values over the past 10 000 yr, and no support for a period of marked, geographically widespread aridification culminating 900-950 yr ago. Instead, increases in grasses at around that time may signal a transition in human land use to a more dedicated agro-pastoralist lifestyle, when megafaunal populations were already in decline. Land use changes ca 1000 yr ago would have simply accelerated the inevitable loss of Madagascar's megafauna.