Department of Biology, Biodiversity Unit, Lund University, Sölvegatan 37, Lund, SE 223 62, Sweden.
Centre for Environmental and Climate Research, Lund University, Sölvegatan 37, Lund, SE 223 62, Sweden.
Ecol Appl. 2019 Jun;29(4):e01875. doi: 10.1002/eap.1875. Epub 2019 Mar 15.
Declines in European farmland birds over past decades have been attributed to the combined effects of agricultural intensification and abandonment. Consequently, aspirations to stop declines should focus attention on reversing these changes through voluntary or policy-driven interventions. The design of such interventions should ideally be informed by scientific knowledge of which aspects of the transformation of agricultural landscapes have contributed to the farmland bird declines. Declines may be associated with loss of natural habitats or the intensification and homogenization of land use management on production land, and furthermore, these changes may interact. Here, we applied an orthogonal design exploiting spatial variation in land use in a major agricultural region of Sweden to seek evidence for benefits to farmland birds of reversing some of the intensifications on and among arable fields and whether effects are modified by the availability of seminatural habitats (pastures and field borders) in the landscape. We accounted for the potentially confounding effect of interactions between species by using a joint species distribution model explicitly controlling for additional variation and covariation among species. We found that interventions aimed specifically at land in production could provide benefits to farmland birds. Landscapes with a higher proportion leys or fallows and/or with a more diverse set of crops held higher abundances of most farmland birds. However, effects were only apparent in landscapes with low availability of seminatural habitats and were sometimes even negative in landscapes with high amounts of such habitats, demonstrating context dependence. Even if we found little evidence of interactions between species, the joint modeling approach provided several benefits. It allowed information to be shared between species making analyses robust to uncertainty due to low abundances and provided direct information about the mean and variability in effects of studied predictors among species. We also found that care needs to be taken regarding prior and distributional assumptions as the importance of species interactions might otherwise be overstated. We conclude that this approach is well suited for evaluating agricultural policies by providing evidence for or against certain interventions or to be linked to policy scenarios of land use change.
几十年来，欧洲农田鸟类数量的减少归因于农业集约化和废弃的综合影响。因此，阻止减少的愿望应该将注意力集中在通过自愿或政策驱动的干预来扭转这些变化上。这些干预措施的设计理想情况下应根据科学知识来指导，了解农业景观转型的哪些方面促成了农田鸟类的减少。减少可能与自然栖息地的丧失或生产土地上土地利用管理的集约化和同质化有关，此外，这些变化可能相互作用。在这里，我们应用了一种正交设计，利用瑞典一个主要农业区土地利用的空间变化，寻求扭转一些农田集约化和同质化的措施对农田鸟类的益处的证据，以及这些措施是否受到景观中半自然栖息地（牧场和农田边界）可用性的影响。我们通过使用联合物种分布模型来明确控制物种之间的额外变化和共变，考虑到物种之间相互作用的潜在混杂效应，该模型为每个物种提供了独特的预测。我们发现，专门针对生产用地的干预措施可能会为农田鸟类带来益处。草地或休耕地比例较高或作物种类更多的景观拥有更多数量的大多数农田鸟类。然而，这些效果仅在半自然栖息地可用性较低的景观中明显，并且在这种栖息地数量较高的景观中有时甚至是负面的，这表明存在背景依赖性。即使我们发现很少有物种之间相互作用的证据，联合建模方法也提供了一些好处。它允许在物种之间共享信息，使分析对由于数量低而导致的不确定性具有稳健性，并提供了有关研究预测因子在物种之间的影响的平均值和可变性的直接信息。我们还发现，需要注意先验和分布假设，因为否则可能会夸大物种相互作用的重要性。我们的结论是，这种方法非常适合通过提供支持或反对某些干预措施的证据，或者与土地利用变化的政策情景相联系，来评估农业政策。
