School of Biological Sciences and Australian Centre for Biodiversity, Monash University, Melbourne, Clayton Campus, Clayton, VIC 3800, Australia.
Ecology. 2012 Jul;93(7):1717-27. doi: 10.1890/11-1891.1.
Understanding the processes leading to population declines in fragmented landscapes is essential for successful conservation management. However, isolating the influence of disparate processes, and dispersal in particular, is challenging. The Grey Shrike-thrush, Colluricincla harmonica, is a sedentary woodland-dependent songbird, with learned vocalizations whose incidence in suitable habitat patches falls disproportionally with decline in tree cover in the landscape. Although it has been suggested that gaps in tree cover might act as barriers to its dispersal, the species remains in many remnants of native vegetation in agricultural landscapes, suggesting that it may have responded to habitat removal and fragmentation by maintaining or even increasing dispersal distances. We quantified population connectivity of the Grey Shrike-thrush in a system fragmented over more than 120 years using genetic (microsatellites) and acoustic (song types) data. First, we tested for population genetic and acoustic structure at regional and local scales in search of barriers to dispersal or gene flow and signals of local spatial structuring indicative of restricted dispersal or localized acoustic similarity. Then we tested for effects of habitat loss and fragmentation on genetic and acoustic connectivity by fitting alternative models of mobility (isolation-by-distance [the null model] and reduced and increased movement models) across treeless vs. treed areas. Birds within -5 km of each other had more similar genotypes and song types than those farther away, suggesting that dispersal and song matching are limited in the region. Despite restricted dispersal detected for females (but not males), populations appeared to be connected by gene flow and displayed some cultural (acoustic) connectivity across the region. Fragmentation did not appear to impact greatly the dispersal of the Grey Shrike-thrush: none of the mobility models fit the genetic distances of males, whereas for females, an isolation-by-distance model could not be rejected in favor of the models of reduced or increased movement through treeless gaps. However, dissimilarities of the song types were more consistent with the model of reduced cultural connectivity through treeless areas, suggesting that fragmentation impedes song type sharing in the Grey Shrike-thrush. Our paper demonstrates that habitat fragmentation hinders important population processes in an Australian woodland bird even though its dispersal is not detectably impacted.
理解导致破碎景观中种群减少的过程对于成功的保护管理至关重要。然而，隔离不同过程的影响，特别是扩散的影响，具有挑战性。灰林鸲，Colluricincla harmonica，是一种久坐的林地依赖鸣禽，具有学习而来的叫声，其在适宜栖息地斑块中的发生率与景观中树冠覆盖率的下降不成比例。尽管有人认为树冠覆盖的缺口可能会成为其扩散的障碍，但该物种仍存在于农业景观中许多原生植被的残余物中，这表明它可能通过维持甚至增加扩散距离来应对栖息地的移除和破碎化。我们使用遗传（微卫星）和声学（鸣叫声型）数据，量化了一个已经破碎超过 120 年的系统中灰林鸲的种群连通性。首先，我们在区域和局部尺度上测试了种群的遗传和声学结构，以寻找扩散或基因流的障碍以及局部空间结构的信号，这些信号表明限制了扩散或局部声学相似性。然后，我们通过在无树区和有树区之间拟合不同的移动性模型（隔离距离模型[零假设]和减少或增加移动性模型），测试了栖息地丧失和破碎化对遗传和声学连通性的影响。彼此相距 -5 公里以内的鸟类比相距较远的鸟类具有更相似的基因型和鸣叫声类型，这表明在该地区扩散和鸣叫声匹配受到限制。尽管检测到雌性（但不是雄性）的扩散受到限制，但种群似乎通过基因流连接，并在整个地区显示出一些文化（声学）连通性。破碎化似乎并没有对灰林鸲的扩散产生很大影响：没有一种移动性模型适合雄性的遗传距离，而对于雌性，无法拒绝隔离距离模型，而支持通过无树缺口减少或增加移动性的模型。然而，鸣叫声类型的差异更符合通过无树区减少文化连通性的模型，这表明破碎化阻碍了灰林鸲的鸣叫声类型共享。我们的论文表明，即使灰林鸲的扩散没有明显受到影响，栖息地破碎化也会阻碍澳大利亚林地鸟类的重要种群过程。
