A central question of community ecology is to understand how the interplay between processes of the Neutral Theory (e.g., immigration and ecological drift) and niche-based processes (e.g., environmental filtering, intra- and interspecific density-dependence) shape species diversity in competitive communities. The articulation between these two categories of mechanisms can be studied through the lens of the intermediate organizational level of "functional groups" (FGs), defined as clusters of species with similar traits. Indeed, FGs stress ecological differences among species and are thus likely to unravel non-neutral interactions within communities. Here we presented a novel approach to explore how FGs affect species coexistence by comparing species and functional diversity patterns. Our framework considers the Neutral Theory as a mechanistic null hypothesis. It assesses how much the functional diversity deviates from species diversity in communities, and compares this deviation, called the "average functional deviation", to a neutral baseline. We showed that the average functional deviation can indicate reduced negative density-dependence or environmental filtering among FGs. We validated our framework using simulations illustrating the two situations. We further analyzed tropical tree communities in Western Ghats, India. Our analysis of the average functional deviation revealed environmental filtering between deciduous and evergreen FGs along a broad rainfall gradient. By contrast, we did not find clear evidence for reduced density-dependence among FGs. We predict that applying our approach to new case studies where environmental gradients are milder and FGs are more clearly associated to resource partitioning should reveal the missing pattern of reduced density-dependence among FGs.

中文翻译：

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用中立理论分析快照多样性模式可以显示功能组对社区组装的影响

群落生态学的一个核心问题是了解中性理论的过程（例如，移民和生态漂移）与基于生态位的过程（例如，环境过滤、种内和种间密度依赖性）之间的相互作用如何在竞争中塑造物种多样性。社区。这两类机制之间的联系可以通过“功能群”（FG）的中间组织级别的镜头进行研究，“功能群”被定义为具有相似特征的物种集群。事实上，FGs 强调物种之间的生态差异，因此可能会破坏社区内的非中性相互作用。在这里，我们提出了一种通过比较物种和功能多样性模式来探索 FG 如何影响物种共存的新方法。我们的框架将中性理论视为机械零假设。它评估功能多样性偏离群落物种多样性的程度，并将这种偏差（称为“平均功能偏差”）与中性基线进行比较。我们表明，平均功能偏差可以表明 FG 之间减少的负密度依赖性或环境过滤。我们使用说明两种情况的模拟验证了我们的框架。我们进一步分析了印度西高止山脉的热带树木群落。我们对平均功能偏差的分析揭示了沿宽降雨梯度的落叶和常绿 FG 之间的环境过滤。相比之下，我们没有发现 FG 之间密度依赖性降低的明确证据。