Mechanistic modeling of environmental drivers of woolly mammoth carrying capacity declines on St. Paul Island.
Mechanistic modeling of environmental drivers of woolly mammoth carrying capacity declines on St. Paul Island.
复制标题
圣保罗岛猛犸象承载能力下降的环境驱动因素的机械模型。
作者：
Yue Wang;W. Porter;P. Mathewson;P. Miller;R. Graham;John W. Williams
在白令陆桥的遗迹圣保罗岛上，猛犸象一直存在到距今 5,600 年，没有已知的捕食者或竞争对手，为研究假设的灭绝环境驱动因素提供了一个自然系统。其中包括气温升高导致的过热、饥饿和干旱。在这里，我们使用 Niche Mapper 和 LPJ-GUESS 来测试这些假设，以机械方式估计猛犸象的代谢率以及饮食和淡水需求，并据此估计过去 17,000 年圣保罗岛屿承载能力的变化。最初与大陆隔离时，人口承载能力可能有数百人。成年猛犸象可能会禁食两到三个月，这表明它们具有获取雪埋草料的必要能力。在全新世期间，植被净初级生产力有所增加，但岛屿面积的缩小超过了净初级生产力（NPP）的增加，将承载能力降低至约100人。在晚更新世和全新世的环境变化期间，NPP 和淡水可用性交替成为该岛屿人口的关键限制因素。火山口湖中的淡水过剩只能维持两到三只个体（在最乐观的参数敏感性实验中最多可达 18 只个体），这表明圣保罗猛犸象种群高度依赖沿海淡水资源。模拟与可用的代理数据一致，同时强调需要从沿海泻湖检索新的古水文代理记录以测试模型预测。更广泛地说，这些发现强化了岛屿巨型食草动物种群对资源限制和灭绝的脆弱性。
On St. Paul Island, a remnant of the Bering Land Bridge, woolly mammoths persisted until 5,600 yr BP with no known predators or competitors, providing a natural system for studying hypothesized environmental drivers of extinction. These include overheating due to rising temperatures, starvation, and drought. Here, we test these hypotheses using Niche Mapper and LPJ-GUESS to mechanistically estimate mammoth metabolic rates and dietary and freshwater requirements and, from these, estimate variations in island carrying capacity on St. Paul for the last 17,000 yr. Population carrying capacity may have been several hundred individuals at the time of initial isolation from the mainland. Adult mammoths could have fasted for two to three months, indicating a necessary ability to access snow-buried forage. During the Holocene, vegetation net primary productivity increased, but shrinking island area overrode increased net primary productivity (NPP), lowering carrying capacity to ~100 individuals. NPP and freshwater availability alternated as critical limiting factors for this island population during the environmental changes of the late Pleistocene and Holocene. Only two or three individuals could have been sustained by the freshwater surplus in crater lakes (up to 18 individuals under the most optimistic parameter sensitivity experiments), suggesting that the St. Paul mammoth population was highly dependent on coastal freshwater sources. The simulations are consistent with the available proxy data, while highlighting the need to retrieve new paleohydrological proxy records from the coastal lagoons to test model predictions. More broadly, these findings reinforce the vulnerability of island megaherbivore populations to resource limitation and extinction.