The Danger of Having All Your Eggs in One Basket—Winter Crash of the Re-Introduced Przewalski's Horses in the Mongolian Gobi

Large mammals re-introduced into harsh and unpredictable environments are vulnerable to stochastic effects, particularly in times of global climate change. The Mongolian Gobi is home to several rare large ungulates such as re-introduced Przewalski's horses (Equus ferus przewalskii) and Asiatic wild asses (Equus hemionus), but also to a millennium-old semi-nomadic livestock herding culture. The Gobi is prone to large inter-annual environmental fluctuations, but the winter 2009/2010 was particularly severe. Millions of livestock died and the Przewalski's horse population in the Gobi crashed. We used spatially explicit livestock loss statistics, ranger survey data and GPS telemetry to provide insight into the effect of a catastrophic climate event on the two sympatric wild equid species and the livestock population in light of their different space use strategies. Herders in and around the Great Gobi B Strictly Protected Area lost on average 67% of their livestock. Snow depth varied locally, resulting in livestock losses following an east-west gradient. Herders had few possibilities for evasion, as competition for available winter camps was high. Przewalski's horses used three different winter ranges, two in the east and one in the west. Losses averaged 60%, but differed hugely between east and west. Space use of Przewalski's horses was extremely conservative, as groups did not attempt to venture beyond their known home ranges. Asiatic wild asses seemed to have suffered few losses by shifting their range westwards. The catastrophic winter 2009/2010 provided a textbook example for how vulnerable small and spatially confined populations are in an environment prone to environmental fluctuations and catastrophes. This highlights the need for disaster planning by local herders, multiple re-introduction sites with spatially dispersed populations for re-introduced Przewalski's horses, and a landscape-level approach beyond protected area boundaries to allow for migratory or nomadic movements in Asiatic wild asses.

被重新引入严酷且不可预测环境中的大型哺乳动物极易受到随机效应（stochastic effects）的影响，在全球气候变化的背景下尤为显著。蒙古戈壁（Mongolian Gobi）栖息着多种珍稀大型有蹄类动物（large ungulates），其中包括重新引入的普氏野马（Przewalski's horses, Equus ferus przewalskii）与亚洲野驴（Asiatic wild asses, Equus hemionus），同时该区域还传承着延续千年的半游牧畜牧文化。戈壁地区年际环境波动幅度较大，而2009/2010年的冬季尤为严酷，数百万头家畜死亡，戈壁内的普氏野马种群数量骤降。我们借助空间显性（spatially explicit）家畜损失统计数据、护林员调查数据与GPS遥测（GPS telemetry）技术，结合两种同域分布（sympatric）野生马科动物的差异化空间利用策略，深入探究了这场灾难性气候事件对这两种物种以及家畜种群的影响：大戈壁B严格保护区（Great Gobi B Strictly Protected Area）及其周边区域的牧民平均损失了67%的家畜，各地积雪深度存在空间异质性，使得家畜损失呈现出东西向梯度分布特征，且由于可用冬季牧场的竞争十分激烈，牧民几乎没有规避风险的迁移空间。普氏野马的冬季活动范围分为三处，东部两处、西部一处，其种群平均损失率为60%，但东西部之间的损失差异极为悬殊；该物种的空间利用策略极为保守，种群群体从未尝试跨越已知的家域范围。亚洲野驴则通过将活动范围西迁，似乎仅遭受了轻微的种群损失。2009/2010年的灾难性冬季为我们提供了一个典型范本，清晰展现了规模较小且空间受限的种群在易于发生环境波动与灾害的环境中是何等脆弱，这一研究结果凸显出三方面的迫切需求：一是当地牧民需制定完善的灾害应对预案；二是针对重新引入的普氏野马，需设立多个空间分布分散的重新引入点以维持种群稳定性；三是需采用超越保护区边界的景观尺度管理策略，为亚洲野驴预留迁徙或游牧活动的空间。