Community assembly theory hypothesizes that two main niche‐based processes act to shape composition and organization of biological assemblages: abiotic filtering and biological interactions. Here, we conducted repeated surveys of bird abundance along an undisturbed elevational gradient in the tropical Andes to investigate 1) signals of deterministic processes driving community assembly and 2) potential mechanisms by which these forces operate (temperature, habitat complexity, fruit and insect availability), while correcting for imperfect detection and modeling species abundances with N‐mixture models. We observed strong signals of abiotic filtering driving functionally and phylogenetically clustered assemblages towards higher elevations, and a weaker signal of limiting similarity resulting in few overdispersed assemblages at lower elevations. Whereas the decay in species richness with increasing elevation was explained by temperature, trait and phylogenetic dispersion were explained by both temperature and vegetation structure, implying that an interplay of abiotic and biotic mechanisms determines abundance‐based community structure in our montane assemblages. Interestingly, trait and phylogenetic dispersion consistently decreased until ~3000 m but increased above this elevation, highlighting a potential role of competition in resource‐scarce habitats. Combined, our findings suggest abiotic filters are still the main process shaping montane biotas across elevations, whereas resource availability might act locally upon assemblages further modifying them. Our study challenges recent studies in tropical mountains that suggest that biotic filters are a stronger force than abiotic filters in shaping tropical montane assemblages, and exemplifies how accounting for imperfect detection might overcome potential biases in detecting environmental filtering signals in community assembly studies.

中文翻译：

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热带海拔梯度上鸟类群落聚集的生态驱动力

社区组装理论假设，基于生态位的两个主要过程可影响生物组装的组成和组织：非生物过滤和生物相互作用。在这里，我们对热带安第斯山脉沿不受干扰的海拔梯度沿鸟类丰度进行了多次调查，以调查1）驱动群落聚集的确定性过程信号，以及2）这些力量发挥作用的潜在机制（温度，栖息地复杂性，水果和昆虫的可利用性） ，同时使用N混合模型校正不完善的检测和建模物种的丰度。我们观察到非功能性过滤的强烈信号，它们在功能上和系统发育上向较高的高度聚集，而在相似性较低的信号较弱的情况下，在较低的高度几乎没有过度分散的聚集。物种丰富度随海拔的升高而下降的现象可以通过温度来解释，而性状和系统发育的分散性则可以通过温度和植被结构来解释，这意味着非生物和生物机制之间的相互作用决定了我们山地植物群落中以丰度为基础的群落结构。有趣的是，性状和系统发育散布持续减少直到〜3000 m，但在此高度以上增加，突显了竞争在资源稀缺的栖息地中的潜在作用。综合来看，我们的研究结果表明，非生物过滤器仍然是跨海拔山地生物群落形成的主要过程，而资源的可用性可能会随着组合的进一步改变而局部发挥作用。