Forest fragmentation is a leading driver of biodiversity loss, yet its effects on positive species interactions remain poorly known. We examined the effects of fragmentation on mixed-species bird flocks in the Western Andes of Colombia. Using 500-m transect surveys (n = 14 transects), we sampled flocks in 8 fragments (range: 10–173 ha) and an unfragmented reference site within the same altitudinal band (1,900–2,200 m.a.s.l.) and matrix type (cattle pasture). We evaluated the relative contributions of 9 predictor variables, including patch size, distance from edge, and selective aspects of vegetation structure on the composition, size, species richness, functional diversity, and phylogenetic diversity of flocks. We found effects of both patch size and vegetation structure on flock species richness, size, and functional diversity, but no support for edge effects. Generally, flock richness and size responded differently to fragmentation than did functional and phylogenetic diversity metrics. Both flock size and richness increased with patch size, but this variable had no effect on functional and phylogenetic diversity. Flock richness and size increased in high-canopy forests with greater foliage height diversity, whereas unlogged, old-growth primary forests with large-diameter trees had lower flock richness and size, but significantly greater functional diversity. Phylogenetic diversity was not affected by patch size, edge effects, or vegetation structure. We found differences in flock composition in response to fragmentation. Richness of Furnariidae in flocks increased with increasing distance from edge and foliage height diversity, whereas that of Thraupidae and boreal migrant species increased in early successional and forest edge flocks, respectively. All flock diversity metrics differed significantly seasonally, with smaller, less diverse flocks observed in January–March than in June–August. Flocking behavior persisted in 10-ha fragments, likely because Andean flocks are “open membership” in nature, but there was extensive species turnover as forest edge and generalist species replaced forest-interior species in smaller fragments.

中文翻译：

---

斑块的大小和植被结构在哥伦比亚西部安第斯山脉的片段大小梯度上驱动混合物种群多样性和组成的变化

森林碎片化是生物多样性丧失的主要驱动力，但其对积极的物种相互作用的影响仍然知之甚少。我们研究了破碎对哥伦比亚西部安第斯山脉混种鸟类的影响。使用500米横断面调查（n= 14个样带），我们在同一高度带（1,900–2,200 masl）和基质类型（牛牧场）内的8个片段（范围：10–173公顷）和无片段的参考位点采样了鸡群。我们评估了9个预测变量的相对贡献，包括斑块大小，距边缘的距离以及植被结构在组成，大小，物种丰富度，功能多样性和群发生系统多样性方面的选择性方面。我们发现斑块大小和植被结构对羊群物种的丰富度，大小和功能多样性的影响，但没有对边缘效应的支持。通常，羊群的丰富度和大小对碎片的反应与功能和系统发育多样性指标的反应不同。羊群的大小和丰富度都随着斑块的大小而增加，但是此变量对功能和系统发育多样性没有影响。高树冠林具有较高的叶面高度多样性，而羊群丰富度和大小增加，而具有大直径树木的未砍伐，老龄原始林的羊群丰富度和大小较低，但功能多样性明显更大。系统发育多样性不受斑块大小，边缘效应或植被结构的影响。我们发现羊群组成对片段化的反应有所不同。随着离边缘和叶片高度多样性距离的增加，Furariidaidae的丰富度增加，而在演替早期和森林边缘的群体中，伞形科和北方移栖物种的丰富度分别增加。所有羊群多样性指标的季节差异都很大，较小，在1月至3月观察到的鸟群比6月至8月少。植树行为在10公顷的碎片中持续存在，这可能是因为安第斯山脉的羊群是自然界中的“开放成员”，但由于森林边缘和通配物种在较小的碎片中替代了森林内部的物种，因此物种交易频繁。