Data from: Unraveling the interplay of community assembly processes acting on multiple niche axes across spatial scales

How the relative importance of community assembly processes varies with spatial scale is the focus of intensive debate, in part because inferring the scales at which specific niche-based processes act is difficult. One obstacle is that standard phylogenetic and functional diversity metrics may integrate the signals of multiple processes when combining separate niche axes into one variable (multiple-niche-axis metrics), potentially obscuring overlapping niche-based processes. We use simulations to evaluate the power of these metrics to detect competition and habitat filtering when these processes operate across multiple niche axes and vary in their relative importance. We then test for both processes at a range of spatial scales in a Neotropical bird assemblage. Simulations revealed that multiple-niche-axis metrics had low power to detect competition and habitat filtering when a mix of both processes acts across niche axes, whereas metrics focused on single-niche axes were better able to deal with this complexity. We found the same contrast in bird communities, where both competition and habitat filtering were detected at the scale of individual territories, but only by single-niche-axis metrics focused on specific niche axes (e.g., foraging traits). Our results suggest that multiple-niche-axis metrics may produce misleading evidence that niche-based processes are partitioned, particularly across scales, and highlight the importance of analyzing functional diversity patterns on individual niche axes when testing assembly models.

群落组装过程的相对重要性如何随空间尺度发生变化，是学界激烈争论的核心议题之一，部分原因在于，推断特定基于生态位（niche）的过程发挥作用的空间尺度颇具挑战。其中一项核心障碍在于，标准的系统发育与功能多样性指标（phylogenetic and functional diversity metrics）在将多个独立生态位轴整合为单一变量时，此类指标被称为多生态位轴指标（multiple-niche-axis metrics），其可能会整合多种过程的信号，进而掩盖相互重叠的基于生态位的过程。我们通过模拟实验，评估了当种间竞争与生境过滤（habitat filtering）这两类过程跨多个生态位轴发挥作用且相对重要性存在差异时，上述指标的检测效能。随后，我们在新热带鸟类群落（Neotropical bird assemblage）的一系列空间尺度上，对这两类过程开展了检验。模拟结果显示，当两类过程同时跨生态位轴发挥作用时，多生态位轴指标检测种间竞争与生境过滤的效能较低；而聚焦单一生态位轴的指标则能更好地应对这类复杂性。在鸟类群落研究中我们得到了一致的对比结果：在个体领域尺度下可同时检测到种间竞争与生境过滤，但这一结果仅能通过聚焦特定生态位轴（如觅食性状（foraging traits））的单一生态位轴指标获得。本研究结果表明，多生态位轴指标可能会生成误导性结论，让人误以为基于生态位的过程是分区存在的，尤其是在跨尺度分析场景下；同时本研究也强调，在检验群落组装模型时，针对单一生态位轴分析功能多样性格局的重要性。