Forest structure, defined as the three-dimensional vertical and horizontal distribution of canopy vegetation, has a great influence on the distribution patterns and abundance of forest primates. The complexity of this structural canopy produces a diverse range of microhabitats and distinct ecological niches, allowing ecologically similar species to coexist. Degradation of forests through anthropogenic factors significantly alters forest structure, and arboreal species such as gibbons are particularly vulnerable to these changes because of their reliance on canopy for survival. We investigated how forest structural variables influenced the density of two sympatric gibbon species (siamangs, Symphalangus syndactylus and lar gibbons, Hylobates lar) in Sikundur, a historically disturbed tropical lowland forest in north Sumatra. We used auditory sampling to establish group density in 10 locations and assessed structural characteristics of forest within 4–6 vegetation plots in each location. Lar gibbon group densities were 0.53–3.10 groups/km² and siamang group densities were lower, with 0.0–1.0 groups/km². The densities of both species were positively influenced by median height of first bole and the percentage of canopy connectivity. Lar gibbon group density was positively related to large (diameter at breast height 30–100 cm), tall (20–25 m) trees with a large crown area (100–300 m²), while siamang group density showed no significant relationships with these variables. These findings show canopy connectivity and height to first bole are significant structural variables for the continued presence of both gibbon species although, ecologically similar species can be influenced by different levels of structural disturbance. This canopy structural variation between sympatric species existing in the same ecosystem allows for home range overlap, low interspecific competition, and coexistence.

森林结构被定义为冠层植被的三维垂直和水平分布，它对森林灵长类动物的分布方式和丰富度具有很大的影响。这种结构性树冠的复杂性产生了各种各样的微生境和独特的生态位，从而使生态相似的物种得以共存。由于人为因素造成的森林退化会极大地改变森林结构，长臂猿等乔木物种特别容易受到这些变化的影响，因为它们依赖于冠层来维持生存。我们研究了森林结构变量如何影响两个同域长臂猿物种（siamangs，密度Symphalangus syndactylus和LAR长臂猿，长臂猿拉尔）位于苏门答腊北部北部历史悠久的热带低地森林西昆杜尔。我们使用听觉采样来建立10个地点的群体密度，并评估每个地点4-6个植被地块内森林的结构特征。Lar长臂猿组的密度为0.53–3.10组/ km ^2，而siamang组的密度较低，为0.0–1.0组/ km ²。两种物种的密度都受到第一胆的中位数高度和树冠连通性百分比的正影响。长臂猿组密度与树冠面积大（100–300 m ²）的大树（胸高30–100 cm的直径），高大（20–25 m）的树呈正相关），而siamang组密度与这些变量没有显着关系。这些发现表明，树冠的连通性和至第一胆的高度是两个长臂猿物种持续存在的重要结构变量，尽管生态相似的物种可能会受到不同程度的结构扰动的影响。同一生态系统中同胞物种之间的冠层结构变化允许家系重叠，种间竞争少和共存。