Department of Conservation Biology, Estación Biológica de Doñana-CSIC, C/Americo Vespucio 26, Seville, 41092, Spain.
Population Ecology Group, Institute for Mediterranean Studies (IMEDEA), CSIC-UIB, Esporles, 07190, Spain.
Ecol Appl. 2021 Apr;31(3):e2266. doi: 10.1002/eap.2266. Epub 2021 Jan 19.
Large, long-lived species with slow life histories and protracted pre-breeding stages are particularly susceptible to declines and extinction, often for unknown causes. Here, we show how demographic modeling of a medium-sized raptor, the Red Kite Milvus milvus, can aid to refocus conservation research and attention on the most likely mechanisms driving its decline. Red Kites' survival and reproduction increased through three sequential stages for 1-2, 3-6, and 7-30 yr of age, mainly corresponding to individuals that are dispersing, attempting to gain a territory, and breeding. As typical of long-lived species, elasticities were highest for adult (≥7 yr old) survival, but this was high, with little scope for improvement. Instead, the declines were driven by an extremely low survival of pre-adults in their first years of life, which weakened the whole demographic system by nullifying the offspring contribution of adults and curtailing their replacement by recruits. For example, 27 pairs were necessary to generate a single prime age adult. Simulation of management scenarios suggested that the decline could be halted most parsimoniously by increasing pre-adult survival to the mean levels recorded for other areas, while only the synergistic, simultaneous improvement of breeding success, adult and pre-adult survival could generate a recovery. We propose three actions to attain such goals through selective supplementary feeding of both breeding and non-breeding individuals, and through mortality improvement by GPS remote-sensing devices employed as surveillance monitoring tools. Our results show how improving demographic models by using real, local vital rates rather than "best guess" vital rates can dramatically improve model realism by refocusing attention on the actual stages and mortality causes in need of manipulation, thus building precious time and resources for conservation management. These results also highlight the frequent key role of pre-adult survival for the management of long-lived species, coherent with the idea of demographic systems as integrated chains only as strong as their weakest link.
大型、长寿、生活史缓慢且繁殖前阶段漫长的物种特别容易减少和灭绝，而且往往原因不明。在这里，我们展示了如何通过对中型猛禽红隼（Milvus milvus）的种群模型进行分析，将保护研究和关注的焦点重新集中在推动其减少的最可能机制上。红隼的存活率和繁殖率在 1-2 岁、3-6 岁和 7-30 岁的三个连续阶段中增加，主要对应于正在扩散、试图获得领地和繁殖的个体。与长寿命物种典型情况一样，成年（≥7 岁）存活率的弹性最高，但这一存活率很高，几乎没有改进的余地。相反，衰退是由幼鸟在生命的头几年极低的存活率驱动的，这削弱了整个种群系统，因为成年个体的后代贡献为零，新个体的补充也受到限制。例如，需要 27 对红隼才能产生一个处于繁殖高峰期的成年个体。管理情景模拟表明，最节省成本的方法是通过提高幼鸟存活率，使其达到其他地区记录的平均水平，从而使衰退得到遏制。只有通过提高繁殖成功率、成年个体和幼鸟存活率的协同作用，才能实现种群的恢复。我们提出了三种行动，通过选择性地为繁殖和非繁殖个体提供补充食物，以及通过 GPS 远程感应设备作为监测工具来提高死亡率，从而实现这些目标。我们的研究结果表明，通过使用真实的、本地的生命表数据来改进生命表模型，而不是使用“最佳猜测”的生命表数据，可以通过将注意力集中在需要操纵的实际阶段和死亡率原因上，极大地提高模型的现实性，从而为保护管理节省宝贵的时间和资源。这些结果还突出了幼鸟存活率在管理长寿物种方面的关键作用，这与将种群系统视为仅由其最薄弱环节决定的整体链条的观点是一致的。
