Does vegetation change over 28 years affect habitat use and reproductive success?

Individuals should prefer and use habitats that confer high fitness, but habitat use is not always adaptive. Vegetation in natural landscapes changes gradually and the ability of species to adaptively adjust their habitat use to long-term changes is largely unstudied. We studied nest patch and territory use over 28 years in Orange-crowned Warblers (Oreothlypis celata) in a system that has undergone natural long-term changes in vegetation. Abundance of maple (Acer grandidentatum), its preferred nesting habitat, has gradually declined from 1987 to 2015. We examined whether habitat use and its fitness consequences changed as the availability of preferred habitat decreased. We used resource selection function models to determine changes over time in the probability of using a nest patch given available patches, and the probability of using a territory given available territories. We estimated nest survival to evaluate changes over time in the fitness consequences of nest patch use. We also compared habitat use (nest patch and territory) and fitness (nest survival) between areas with naturally reduced abundance of maple and experimentally increased abundance of maple (fenced areas). Nest patch use depended on maple abundance and did not change drastically across 28 years, even though the availability of preferred maple patches decreased over time. In contrast, nest survival tended to decrease over time. We did not see differences in nest patch use and nest survival between unfenced and fenced areas, unlike territory use, which increased with the abundance of maple in fenced areas and decreased in unfenced areas. Our study depicts one example of relatively unchanged habitat use in the face of decreased availability of preferred vegetation across years, with a resulting decrease in reproductive success. Investigating changes in habitat use and fitness consequences for animals exposed to long-term habitat change is necessary to understand adaptive behavioral responses.

动物通常会偏好并利用能提升自身适合度的栖息地，但栖息地选择并非总具有适应性。自然景观中的植被会逐渐发生变化，然而物种针对长期环境变化适应性调整栖息地选择的能力，目前尚未得到充分研究。我们针对经历了长期自然植被变化的研究区域内的橙冠虫森莺（Orange-crowned Warbler, *Oreothlypis celata*），开展了长达28年的巢域斑块与领地选择行为研究。该物种偏好的筑巢栖息地——大齿槭（Acer grandidentatum）的种群数量，在1987年至2015年间逐渐减少。我们探究了随着偏好栖息地可获得性下降，栖息地选择行为及其对应的适合度效应是否发生了变化。我们采用资源选择函数（resource selection function）模型，分析了在已知可利用巢域斑块的前提下，选择某一巢域斑块的概率随时间的变化，以及已知可利用领地的前提下，选择某一领地的概率随时间的变化。我们通过估算巢存活率，评估了巢域斑块选择对应的适合度效应随时间的变化情况。此外，我们还对比了两类区域的栖息地选择（巢域斑块与领地）与适合度指标（巢存活率）：一类是自然发生大齿槭种群数量下降的区域，另一类是通过人工干预提升大齿槭种群数量的围栏实验区域。尽管偏好的大齿槭巢域斑块可获得性随时间下降，但巢域斑块的选择仅与大齿槭种群数量相关，且在28年间未发生显著变化。与之形成对比的是，巢存活率随时间呈现下降趋势。与领地选择不同，围栏实验区与未围栏区域的巢域斑块选择与巢存活率均未出现显著差异：围栏实验区的领地选择随大齿槭种群数量提升而增加，未围栏区域则随其减少而下降。本研究展示了一个典型案例：面对多年来偏好植被可获得性的下降，动物的栖息地选择并未发生明显改变，但最终导致繁殖成功率降低。针对长期经历栖息地变化的动物开展栖息地选择与适合度效应的相关研究，对于理解其适应性行为响应至关重要。