Habitat loss is the primary driver of the decline of biodiversity in ecological communities. However, which ecological processes are implicated in the removal of species following habitat loss, i.e. the disassembling of the community, remains unclear in many ecosystems. We address this question by investigating how the taxonomic and functional diversity of bird assemblages are related to fragment size in the Atlantic Forest from northeastern Brazil. We used complementary metrics of diversity and a randomization procedure to test whether changes in diversity result from either random or deterministic processes, such as limiting similarity or habitat filtering. The species–area (SAR) and functional richness–area (FAR) relationships were positive, as expected. However, the FAR had a lower slope than the SAR, which indicates a slower loss of functional richness than that predicted by the loss of species richness. Communities in smaller fragments contain more functionally overdispersed species and a more even distribution of abundance. These results indicate that limiting similarity drives the disassembling of bird assemblages in small fragments of the Atlantic Forest, which presumably reflects increased competition. This dynamic tends to reduce functional redundancy in the impoverished assemblages, with potentially deleterious consequences for ecosystem functioning and forest conservation.

生境的丧失是生态社区生物多样性减少的主要驱动力。然而，在许多生态系统中尚不清楚哪个生态过程与栖息地丧失后物种的清除（即社区的瓦解）有关。我们通过研究鸟类组合的分类学和功能多样性与巴西东北部大西洋森林中的碎片大小之间的关系来解决这个问题。我们使用了多样性的补充指标和随机化程序来测试多样性的变化是由随机过程还是确定性过程（例如限制相似性或栖息地过滤）导致的。如预期的那样，物种-区域（SAR）和功能丰富性-区域（FAR）的关系是正的。但是，FAR的坡度比SAR低，这表明功能丰富度的丧失比物种丰富度的丧失所预测的要慢。较小碎片中的社区包含更多功能过度分散的物种和更均匀的丰度分布。这些结果表明，有限的相似性驱使大西洋森林小片段中鸟类的分解，这大概反映了竞争的加剧。这种动态趋向于减少贫困群体的功能冗余，从而对生态系统功能和森林保护产生潜在的有害后果。这些结果表明，有限的相似性驱使大西洋森林小片段中鸟类的分解，这大概反映了竞争的加剧。这种动态趋向于减少贫困群体的功能冗余，从而对生态系统功能和森林保护产生潜在的有害后果。这些结果表明，有限的相似性驱使大西洋森林小片段中鸟类的分解，这大概反映了竞争的加剧。这种动态趋向于减少贫困群体的功能冗余，从而对生态系统功能和森林保护产生潜在的有害后果。