The boreal forest is one of the world’s ecosystems most affected by global climate warming. The snowshoe hare, its predators, and their population dynamics dominate the mammalian component of the North American boreal forest. Our past research has shown the 9–11-year hare cycle to be predator driven, both directly as virtually all hares that die are killed by their predators, and indirectly through sublethal risk effects on hare stress physiology, behavior, and reproduction. We replicated this research over the entire cycle by measuring changes in predation risk expected to drive changes in chronic stress. We examined changes in hare condition and stress axis function using a hormonal challenge protocol in the late winter of 7 years—spanning all phases of the cycle from the increase through to the low (2014–2020). We simultaneously monitored changes in hare abundance as well as those of their primary predators, lynx and coyotes. Despite observing the expected changes in hare–predator numbers over the cycle, we did not see the predicted changes in chronic stress metrics in the peak and decline phases. Thus, the comprehensive physiological signature indicative of chronic predator-induced stress seen from our previous work was not present in this current cycle. We postulate that hares may now be increasingly showing behavior-mediated rather than stress-mediated responses to their predators. We present evidence that increases in primary productivity have affected boreal community structure and function. We speculate that climate change has caused this major shift in the indirect effects of predation on hares.

北方森林是世界上受全球气候变暖影响最严重的生态系统之一。雪兔、它的捕食者和它们的种群动态支配着北美北方森林的哺乳动物组成部分。我们过去的研究表明，9 到 11 年的野兔周期是由捕食者驱动的，这既直接是因为几乎所有死亡的野兔都被其捕食者杀死，也间接通过对野兔应激生理、行为和繁殖的亚致死风险影响。我们通过测量预期会推动慢性压力变化的捕食风险变化，在整个周期中重复了这项研究。我们在 7 年的冬末使用荷尔蒙挑战协议检查了野兔状况和压力轴功能的变化 - 跨越周期的所有阶段，从增加到低谷（2014-2020）。我们同时监测了野兔及其主要捕食者猞猁和郊狼数量的变化。尽管观察到野兔捕食者数量在整个周期中的预期变化，但我们没有看到高峰和衰退阶段慢性压力指标的预测变化。因此，从我们之前的工作中看到的表明慢性捕食者引起的压力的综合生理特征在当前周期中不存在。我们假设野兔现在可能越来越多地对它们的捕食者表现出行为介导的反应，而不是压力介导的反应。我们提供的证据表明初级生产力的提高影响了北方群落结构和功能。我们推测，气候变化导致捕食对野兔的间接影响发生了这种重大转变。