The creation of mega-hydropower dams inundates vast lowland areas, causing widespread environmental impacts in tropical forest regions. Few studies, however, have taken advantage of these newly fragmented landscapes to examine the effects of habitat insularization on arthropod faunas. Here, we assess how dung beetle assemblages respond to 30 years of post-isolation history in forest islands within a major hydroelectric reservoir in Central Amazonia. We sampled 30 of the 3546 islands created by this reservoir, and three neighbouring forest sites. We collected a total of 865 individuals representing 34 dung beetle species and 15 genera. Remarkably, one third of all islands had been entirely defaunated of dung beetles in terms of overall occupancy. Isolation was the single best predictor of dung beetle species richness, followed by the interaction between isolation and island area, and these variables were key determinants of the relict species composition. Isolation was the most important predictor of dung beetle abundance, but area alone was the main predictor of abundance when the dominant species was excluded. We predicted species richness across all 3546 islands, indicating that 61.5% of all islands likely retain only a single ‘super-tramp’ species (Onthophagus osculatii). These community disassembly patterns were likely aggravated by the marked hostility of the open-water matrix combined with the poor flight dispersal capacity of dung beetles over wide gaps between insular forests. As such, the overwhelming number of small, isolated islands created by major dams has profound effects on regional forest biodiversity, including wholesale local extinctions in detritivore assemblages and their ecosystem functions.

巨型水坝的形成淹没了广大的低地地区，在热带森林地区造成了广泛的环境影响。然而，很少有研究利用这些新近破碎的景观来研究栖息地隔离对节肢动物的影响。在这里，我们评估了甲虫组合如何响应中亚马孙地区一个主要水力库中的森林岛屿中的30年隔离后历史。我们采样了由该水库创建的3546个岛屿中的30个，以及三个相邻的森林地点。我们总共收集了865个个体，分别代表34个and类和15个属。值得注意的是，就总入住率而言，所有岛屿中有三分之一已完全被粪便甲虫摧毁。隔离是粪甲虫物种丰富度的唯一最佳预测指标，其次是隔离与岛屿面积之间的相互作用，这些变量是遗迹物种组成的关键决定因素。隔离是粪甲虫丰度的最重要预测因子，但是当排除优势种时，面积是丰度的主要预测因子。我们预测了所有3546个岛屿的物种丰富度，这表明所有岛屿中有61.5％可能仅保留一个“超级流浪者”物种（tho虫（Onthophagus osculatii）。露天水基质的明显敌对性以及粪甲虫在岛林之间的宽阔空隙中的较弱的飞行扩散能力，加重了这些群落的分解方式。因此，由大坝形成的绝大多数孤立小岛对区域森林生物多样性具有深远的影响，包括在局部灭绝的有害生物及其生态系统功能。