The long-distance migration of the eastern Monarch butterfly (Danaus plexippus) is in decline primarily due to habitat loss. Current habitat restoration programs focus on re-establishing milkweed, the monarch larvae' primary food source, in the central United States of America. However, individual components of the monarch life cycle function as part of an integrated whole. Here we develop the MOBU-SDM, a migration-wide systems dynamics model of the Monarch butterfly migratory cycle to explore management strategies' impacts. Our model offers several advances over previous efforts, considering complex variables such as dynamic temperature-dependent developmental times, dynamic habitat availability, and weather-related mortality across the entire range. We first explored whether the predominant focus of milkweed restoration in the mid-range of the monarch’s migration could be overestimating the Monarch's actual habitat requirements. Second, we examined the robustness of using the recommended 1.2-1.6 billion milkweed stems as a policy objective when accounting for factors such as droughts, changes in temperature, and the stems’ effective usability by the Monarchs. Third, we used the model to estimate the number and distribution of stems across the northern, central, and southern regions of the breeding range needed to reach a self-sustainable long-term Monarch population of 6 overwintering hectares. Our analysis revealed that concentrating milkweed growth in the central region increases the size of the overwintering colonies more so than equivalent growth in the south region, with growth in the northern region having a negligible effect. However, even though simulating an increase in milkweed stems in the south did not play a key role in increasing the size of the overwintering colonies, it plays a paramount role in keeping the population above a critically small size. Abiotic factors considerably influenced the actual number of stems needed, but, in general, our estimates of required stems were 43%-91% larger than the stems currently set as a restoration target: our optimal allocation efforts were 7.35%, 92%, and 0.15% to the south, central, and northern regions, respectively. The MOBU-SDM provided us with new avenues to investigate the butterfly migration as a complex biological system and contribute to more robust restoration policies for this unique species.

中文翻译：

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东部帝王蝶恢复资源分配的景观水平评估

东部帝王蝶（Danaus plexippus）的长途迁徙正在减少，主要原因是栖息地的丧失。当前的栖息地恢复计划的重点是在美利坚合众国中部重建马利筋草（君主幼虫的主要食物来源）。但是，君主生命周期的各个组成部分作为集成整体的一部分起作用。在这里，我们开发了MOBU-SDM，这是帝王蝶迁移周期的全迁移系统动力学模型，以探索管理策略的影响。考虑到复杂的变量，例如动态依赖温度的发育时间，动态栖息地可用性以及整个范围内与天气相关的死亡率，我们的模型比以前的工作提供了一些进步。我们首先探讨了君主迁徙中期中马利筋恢复的主要重点是否可能高估了君主的实际栖息地需求。其次，我们在考虑干旱，气温变化以及君主对茎的有效可用性等因素时，研究了使用推荐的1.2-16亿马利筋作为政策目标的稳健性。第三，我们使用该模型估算了达到6个越冬公顷的可自我维持的长期君主种群所需的繁殖范围的北部，中部和南部区域的茎的数量和分布。我们的分析表明，与南部地区的同等生长相比，集中在中部地区的马利筋生长增加了越冬菌落的规模，北部地区的增长影响可忽略不计。但是，即使模拟南部马利筋茎的增加对增加越冬菌落的规模没有起到关键作用，但在使种群保持在极小规模以上的过程中，它却起着至关重要的作用。非生物因素极大地影响了所需茎的实际数量，但总的来说，我们对所需茎的估计数比当前设定为恢复目标的茎大43％-91％：我们的最佳分配努力为7.35％，92％和南部，中部和北部地区分别占0.15％。MOBU-SDM为我们提供了研究蝴蝶作为复杂生物系统迁移的新途径，并为该独特物种的更健壮恢复政策做出了贡献。尽管模拟南部马利筋茎的增加对增加越冬菌落的规模没有起到关键作用，但它在使种群保持在极小规模以上方面起着至关重要的作用。非生物因素极大地影响了所需茎的实际数量，但总的来说，我们对所需茎的估计数比当前设定为恢复目标的茎大43％-91％：我们的最佳分配努力为7.35％，92％和南部，中部和北部地区分别占0.15％。MOBU-SDM为我们提供了研究蝴蝶作为复杂生物系统迁移的新途径，并为该独特物种的更健壮恢复政策做出了贡献。尽管模拟南部马利筋茎的增加对增加越冬菌落的规模没有起到关键作用，但它在使种群保持在极小规模以上方面起着至关重要的作用。非生物因素极大地影响了所需茎的实际数量，但总的来说，我们对所需茎的估计数比当前设定为恢复目标的茎大43％-91％：我们的最佳分配努力为7.35％，92％和南部，中部和北部地区分别占0.15％。MOBU-SDM为我们提供了研究蝴蝶作为复杂生物系统迁移的新途径，并为该独特物种的更健壮恢复政策做出了贡献。