Rushing Clark S, Marra Peter P, Studds Colin E
Migratory Bird Center Smithsonian Conservation Biology Institute National Zoological Park Washington DC USA.
Department of Geography & Environmental Systems University of Maryland Baltimore County Baltimore MD USA.
Ecol Evol. 2017 Apr 21;7(11):3847-3855. doi: 10.1002/ece3.2605. eCollection 2017 Jun.
Determining the geographic connections between breeding and nonbreeding populations, termed migratory connectivity, is critical to advancing our understanding of the ecology and conservation of migratory species. Assignment models based on stable isotopes historically have been an important tool for studying migratory connectivity of small-bodied species, but the low resolution of these assignments has generated interest into combining isotopes with other sources in information. Abundance is one of the most appealing data sources to include in isotope-based assignments, but there are currently no statistical methods or guidelines for optimizing the contribution of stable isotopes and abundance for inferring migratory connectivity. Using known-origin stable-hydrogen isotope samples of six Neotropical migratory bird species, we rigorously assessed the performance of assignment models that differentially weight the contribution of the isotope and abundance data. For two species with adequate sample sizes, we used Pareto optimality to determine the set of models that simultaneously minimized both assignment error rate and assignment area. We then assessed the ability of the top models from these two species to improve assignments of the remaining four species compared to assignments based on isotopes alone. We show that the increased precision of models that include abundance is often offset by a large increase in assignment error. However, models that optimally weigh the abundance data relative to the isotope data can result in higher precision and, in some cases, lower error than models based on isotopes alone. The top models, however, depended on the distribution of relative breeding abundance, with patchier distributions requiring stronger downweighting of abundance, and we present general guidelines for future studies. These results confirm that breeding abundance can be an important source of information for studies investigating broad-scale movements of migratory birds and potentially other taxa.
确定繁殖种群和非繁殖种群之间的地理联系（即迁徙连通性）对于深化我们对迁徙物种的生态和保护的理解至关重要。基于稳定同位素的分配模型历来是研究小型物种迁徙连通性的重要工具，但这些分配的低分辨率引发了将同位素与其他信息来源相结合的兴趣。丰度是基于同位素的分配中最具吸引力的数据源之一，但目前尚无用于优化稳定同位素和丰度对推断迁徙连通性贡献的统计方法或指南。我们使用六种新热带迁徙鸟类的已知来源稳定氢同位素样本，严格评估了对同位素和丰度数据贡献进行不同加权的分配模型的性能。对于两个样本量充足的物种，我们使用帕累托最优性来确定同时最小化分配错误率和分配面积的模型集。然后，我们评估了这两个物种的顶级模型与仅基于同位素的分配相比，改善其余四个物种分配的能力。我们表明，包含丰度的模型精度提高往往被分配错误的大幅增加所抵消。然而，相对于同位素数据对丰度数据进行最优加权的模型可以带来更高的精度，并且在某些情况下，比仅基于同位素的模型具有更低的错误率。然而，顶级模型取决于相对繁殖丰度的分布，分布越分散的情况需要对丰度进行更强的权重下调，我们为未来的研究提供了一般指南。这些结果证实，繁殖丰度可以成为研究候鸟及潜在其他类群大规模迁徙的重要信息来源。
