Unravelling the annual cycle in a migratory animal: breeding-season habitat loss drives population declines of monarch butterflies
Unravelling the annual cycle in a migratory animal: breeding-season habitat loss drives population declines of monarch butterflies
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DOI：
10.1111/1365-2656.12253
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发表时间：
2015-01-01
影响因子：
4.8
通讯作者：
Martin, Tara G.
中科院分区：
文献类型：
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作者：
Flockhart, D. T. Tyler;Pichancourt, Jean-Baptiste;Martin, Tara G.
对迁徙动物的威胁可能发生在一年周期的多个时期，这些时期相隔数千公里，跨越国际边界。在过去的21年里，北美东部的标志性帝王蝶（Danaus plexippus）的数量已经下降。有三种假设可以解释这种下降：墨西哥越冬地的栖息地丧失，美国和加拿大繁殖地的栖息地丧失以及极端天气事件。我们的目标是评估人口的生存能力，确定哪个生命阶段，季节和地理区域是最有助于人口动态和测试的三个假设，解释观察到的人口下降。我们开发了一个空间结构化的，随机的和密度依赖的周期性投影矩阵模型，集成了跨年度周期的迁移连接和人口动态率的模式。我们使用扰动分析，以确定人口丰度的生命率之间的生命阶段，季节和地理区域的变化的敏感性。接下来，我们将每个威胁的单一影响与所有因素同时作用的完整模型进行了比较。最后，我们生成了预测，以评估转基因作物对当前和未来帝王蝶种群规模和灭绝概率造成的宿主植物损失风险。我们的全年人口模型预测人口下降14%和准灭绝概率（世纪内为5%）。君主丰富的繁殖地比越冬地的重要率的扰动敏感四倍以上。仅考虑墨西哥森林损失或气候变化的模拟预测，与繁殖地的乳草下降相比，种群规模更大。我们的模型预测还表明，减轻转基因作物的负面影响会导致更高的种群规模和更低的灭绝风险。最近的种群下降是由于美国的马利筋宿主植物减少，这是由于越来越多地采用转基因作物和土地使用变化，而不是由于墨西哥的气候变化或森林生境退化。因此，减少寄主植物损失对繁殖地的负面影响是减缓或阻止北美帝王蝶未来种群下降的首要保护任务。
Threats to migratory animals can occur at multiple periods of the annual cycle that are separated by thousands of kilometres and span international borders. Populations of the iconic monarch butterfly (Danaus plexippus) of eastern North America have declined over the last 21years. Three hypotheses have been posed to explain the decline: habitat loss on the overwintering grounds in Mexico, habitat loss on the breeding grounds in the United States and Canada, and extreme weather events. Our objectives were to assess population viability, determine which life stage, season and geographical region are contributing the most to population dynamics and test the three hypotheses that explain the observed population decline. We developed a spatially structured, stochastic and density-dependent periodic projection matrix model that integrates patterns of migratory connectivity and demographic vital rates across the annual cycle. We used perturbation analysis to determine the sensitivity of population abundance to changes in vital rate among life stages, seasons and geographical regions. Next, we compared the singular effects of each threat to the full model where all factors operate concurrently. Finally, we generated predictions to assess the risk of host plant loss as a result of genetically modified crops on current and future monarch butterfly population size and extinction probability. Our year-round population model predicted population declines of 14% and a quasi-extinction probability (5% within a century. Monarch abundance was more than four times more sensitive to perturbations of vital rates on the breeding grounds than on the wintering grounds. Simulations that considered only forest loss or climate change in Mexico predicted higher population sizes compared to milkweed declines on the breeding grounds. Our model predictions also suggest that mitigating the negative effects of genetically modified crops results in higher population size and lower extinction risk. Recent population declines stem from reduction in milkweed host plants in the United States that arise from increasing adoption of genetically modified crops and land-use change, not from climate change or degradation of forest habitats in Mexico. Therefore, reducing the negative effects of host plant loss on the breeding grounds is the top conservation priority to slow or halt future population declines of monarch butterflies in North America.