Terrestrial animals are negatively affected by habitat loss, which is assessed on a landscape scale, whereas secondary effects of habitat loss, such as crowding, are usually disregarded. Such impacts are inherently hard to address and poorly understood, and there is a growing concern that they could have dire consequences. We sampled birds throughout a deforestation process to assess crowding stress in an adjacent habitat remnant in the southern Brazilian Atlantic Forest. Crowding is expected of highly mobile taxa, especially given the microhabitat heterogeneity of Neotropical forests, and we hypothesized that the arrival of new individuals or species in refuges shifts assemblage patterns. We used point counts to obtain bird abundances in a before-after-control-impact design sampling of a deforestation event. Temporal changes in taxonomic and functional diversity were examined with metrics used to assess alpha and beta diversity, turnover of taxonomic and functional similarity, and taxonomic and functional composition. Over time increased abundance of some species altered the Simpson index and affected the abundance-distribution of traits in the habitat remnant. Taxonomic composition and functional composition changed in the remnant, and thus bird assemblages changed over time. Taxonomic and functional metrics indicated fugitives affected resident assemblages in refuges, and effects endured >2 years after the deforestation processes had ceased . Dissimilarity of taxonomic composition between pre- and postdeforestation assemblages increased, whereas functional composition reverted to pre-impact conditions We found that ecological disruptions resulted from crowding and escalated into disruptions of species' assemblages and impoverishment of ecosystem functioning. It is important to consider crowding effects of highly mobile taxa during impact assessments, especially in large-scale infrastructures projects that may affect larger areas than is assumed. Article impact statement: The effects of crowding from habitat loss can be an important secondary disturbance to highly mobile animal assemblages. This article is protected by copyright. All rights reserved.

中文翻译：

---

栖息地丧失导致的拥挤对物种组合模式的影响

陆生动物受到栖息地丧失的负面影响，这是在景观尺度上评估的，而栖息地丧失的次要影响，例如拥挤，通常被忽视。这种影响本质上很难解决，也很难理解，人们越来越担心它们可能会产生可怕的后果。我们在整个森林砍伐过程中对鸟类进行采样，以评估巴西南部大西洋森林邻近栖息地残余的拥挤压力。高度流动的分类群预计会拥挤，特别是考虑到新热带森林的微生境异质性，我们假设新个体或物种进入避难所会改变组合模式。我们使用点计数来获得森林砍伐事件前后控制影响设计抽样中的鸟类丰度。使用用于评估 alpha 和 beta 多样性、分类和功能相似性的周转以及分类和功能组成的指标来检查分类和功能多样性的时间变化。随着时间的推移，一些物种的丰度增加改变了辛普森指数，并影响了栖息地残余中性状的丰度分布。残余物中的分类组成和功能组成发生了变化，因此鸟类组合随时间而变化。分类学和功能指标表明逃犯影响了避难所中的居民群体，并且在森林砍伐过程停止后持续了 2 年以上。森林砍伐前和砍伐后组合之间分类学组成的差异增加，而功能组成恢复到影响前的条件我们发现生态破坏是由拥挤引起的，并升级为物种组合的破坏和生态系统功能的贫乏。在影响评估期间考虑高度流动的分类群的拥挤效应很重要，特别是在可能影响比假设更大区域的大型基础设施项目中。文章影响声明：栖息地丧失造成的拥挤影响可能是对高度流动的动物群落的重要二次干扰。本文受版权保护。版权所有。尤其是在可能影响比预期更大区域的大型基础设施项目中。文章影响声明：栖息地丧失造成的拥挤影响可能是对高度流动的动物群落的重要二次干扰。本文受版权保护。版权所有。尤其是在可能影响比预期更大区域的大型基础设施项目中。文章影响声明：栖息地丧失造成的拥挤影响可能是对高度流动的动物群落的重要二次干扰。本文受版权保护。版权所有。