RAPID: Population viability below the quasi-extinction threshold

有时，以前广泛分布的物种已经减少到灭绝。例如，候鸽曾经在北美到处都是，但现在已经不存在了。我们通常知道导致一个广泛分布的物种数量下降的因素（以旅鸽为例，最初的原因是狩猎），但我们对导致一些种群恢复的原因知之甚少，而另一些种群则没有，一旦减少的原始原因消失了。黑脉金斑蝶在北美的数量急剧下降，现在西部的种群可能濒临灭绝。在80年代？年，数以百万计的黑脉金斑蝶在加利福尼亚海岸越冬，并在落基山脉以西的夏季繁殖。到2000年？年，越冬蝴蝶的数量下降到约20 -30万只。2018年，蝴蝶数量下降到3万只左右。这个RAPID项目将利用西方帝王蝶意想不到的快速下降来检验灭绝风险理论。我们将通过精心控制的实验和在整个西部，特别是在加利福尼亚寻找帝王蝶的志愿者报告的目击报告，来评估这个突然减少的种群发生了什么变化。我们将利用这些知识来帮助指导这种标志性蝴蝶种群的管理和恢复。这项研究将验证这样一种假设，即当种群变得非常小时，像存活率和繁殖率这样的重要比率就会下降，这可能是因为单个动物很难找到配偶，或者不能像在群体中那样保护自己免受捕食者的侵害。如果非常小的种群由于这些“狭道效应”而减少，那么在局部种群灭绝之前，就有一个短暂的时间窗口来研究种群动态。由于我们对种群突然减少知之甚少，生态学家通常将保护计划的基础建立在预测种群数量下降到1 ？quasi-extinction阈值?换句话说，低于这个数量，物种就不可能恢复。根据对在越冬地生存和早春繁殖的估计，早期的研究警告说，3万只蝴蝶可能是西方帝王蝶的准灭绝阈值。该项目将(1)测试冬季存活率和春季繁殖是否比过去低；(2)计算夏季范围扩张率，并将2019年与最近几年进行比较，以评估在其他生命阶段生存、繁殖或运动的潜在减少；(3)将(1)和(2)的结果与现有数据相结合，模拟该迁徙种群的全年周期动态。该模型将用于计算小种群和大种群的年种群增长率，并评估不同管理策略的潜力，以帮助西部帝王蝶从准灭绝中恢复过来。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

From time to time, formerly widespread species have declined to extinction. For example, passenger pigeons were once abundant throughout North America, but no longer exist. We often know about the factors that cause a widespread species to decline (in the case of the passenger pigeon, the original cause was hunting), but we know much less about what causes some populations to recover, and others not to do so, once that original cause of declines is gone. Monarch butterfly populations have declined dramatically in North America, and now western populations may be approaching extinction. In the 1980?s, millions of monarch butterflies overwintered on the California coast, and bred during the summer west of the Rocky Mountains. By the 2000?s, the overwintering population had declined to ~200,000-300,000 butterflies. In 2018, the population dropped to ~30,000 butterflies. This RAPID project will use the unexpected, rapid decline of western monarch butterflies to test theories of extinction risk. We will evaluate what changes in this suddenly-small population, through a combination of carefully controlled experiments and sightings reported by volunteers looking for monarch butterflies throughout the west, especially in California. We will use this knowledge to help guide management and recovery of this iconic butterfly population.The research will test the hypothesis that vital rates, like survival and reproduction, decline as populations become very small, perhaps because individual animals have difficulty finding mates, or cannot protect themselves from predators as well as they could in groups. If very small populations decline due to these "Allee effects", there is a fleeting window of time in which to study population dynamics before local population extinction. Because we know so little about suddenly-small populations, ecologists typically base conservation plans on predicting declines to a ?quasi-extinction threshold?, in other words, a population size below which the species is unlikely to be able to recover. Based upon estimates of survival on overwintering grounds and reproduction in early spring, earlier work warned that 30,000 butterflies may be a quasi-extinction threshold for western monarchs. This project will (1) Test whether winter survival and spring reproduction are now lower than they were in the past; (2) Calculate rates of summer range expansion, and compare 2019 to years in the recent past, to evaluate potential reductions of survival, reproduction, or movement at other life stages; (3) Combine results of (1) & (2) with existing data to model dynamics of this migratory population through its full annual cycle. This model will be used to calculate annual population growth rates in small and large populations, and also to evaluate the potential of different management strategies to help western monarch butterflies recover from quasi-extinction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.