Data from: Island-wide aridity did not trigger recent megafaunal extinctions in Madagascar

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. 1,000 years 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 (δ15N) 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 δ15N values culminating in the highest values at the time of proposed maximum drought at ca. 1,000 years 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 δ15N values over time. After accounting for the confounding influences of diet, geographic region, and coastal proximity, we find no change in δ15N values over the past 10,000 years, and no support for a period of marked, geographically widespread aridification culminating 900-950 years 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. 1,000 years ago would have simply accelerated the inevitable loss of Madagascar's megafauna.

针对马达加斯加岛晚全新世特有大型动物群灭绝事件的触发因素，学界在人类活动与气候因子的相对重要性上存在分歧。具体而言，约1000年前出现的木本花粉显著同步减少与草本花粉增加，曾被分别解读为气候干旱化、人类活动加剧，或二者共同作用的证据。
由于干旱化与人为森林砍伐对植被的影响模式相似，厘清二者（若其中之一）中哪一个导致了马达加斯加巨型动物群（megafauna）的灭绝，始终是学界的难题。
本研究利用经放射性碳定年的亚化石脊椎动物的稳定氮同位素（stable nitrogen isotope，δ15N）值，以区分自然变化与人类活动诱导变化的相对重要性。
若巨型动物群的衰退由干旱加剧所致，则我们可预期全岛范围内的δ15N值会持续升高，并在约1000年前的推测极端干旱期达到峰值。
反之，若气候相对稳定，且孢粉信号（palynological signal）的变化可由人类活动对栖息地的改造所解释，则我们可预期栖息地湿度几乎无变化，且δ15N值也不会出现系统性的定向时间变化。
在控制了饮食、地理区域与距海岸距离等混淆变量的影响后，本研究发现过去10000年间δ15N值未发生显著变化，也未找到支持900-950年前出现区域性广泛极端干旱期的证据。
相反，同期草本植物占比的上升，或反映了在巨型动物群已处于衰退阶段时，人类土地利用方式向更为专一的农牧混合生计模式（agro-pastoralist lifestyle）转变。
约1000年前的土地利用变化，不过是加速了马达加斯加巨型动物群本已不可避免的灭绝进程。