Data from: Geographical variation in community divergence: insights from tropical forest monodominance by ectomycorrhizal trees

Convergence occurs in both species traits and community structure, but how convergence at the two scales influences each other remains unclear. To address this question, we focus on tropical forest monodominance, in which a single, often ectomycorrhizal (EM), tree species occasionally dominates forest stands within a landscape otherwise characterized by diverse communities of arbuscular mycorrhizal (AM) trees. Such monodominance is a striking potential example of community divergence resulting in alternative stable states. However, it is observed only in some tropical regions. A diverse suite of AM and EM trees locally co-dominate forest stands elsewhere. We develop a hypothesis to explain this geographical difference using a simulation model of plant community assembly. Simulation results suggest that, in a region with a few EM species (e.g., South America), EM trees experience strong selection for convergent traits that match the abiotic conditions of the environment.
Consequently, EM species successfully compete against other species to form monodominant stands via positive plant-soil feedbacks. By contrast, in a region with many EM species (e.g., Southeast Asia), species maintain divergent traits because of complex plant-soil feedbacks, with no species having traits that enable monodominance. An analysis of plant trait data from Borneo and Peruvian Amazon was inconclusive. Overall, this work highlights the utility of geographical comparison in understanding the relationship between trait convergence and community convergence.

物种性状与群落结构均存在趋同现象，但两类尺度的趋同过程如何相互影响仍尚不明确。为解答该问题，本研究聚焦热带森林单优群落：即某一（通常为外生菌根（ectomycorrhizal, EM）的）树种，在原本以丛枝菌根（arbuscular mycorrhizal, AM）树种多样群落为特征的景观中，偶尔占据林分优势的现象。这类单优群落是引发交替稳定态的群落分化的典型案例之一，但该现象仅在部分热带区域被观测到；在其他区域，则是多样的AM与EM树种局部共占林分。
本研究通过植物群落组装的模拟模型，提出解释这一地理差异的假说。模拟结果显示，在EM树种较少的区域（如南美洲），EM树种会经历强烈的选择压力，演化出匹配环境非生物条件的趋同性状；由此，EM树种可通过正植物-土壤反馈（positive plant-soil feedbacks）成功竞争过其他物种，形成单优林分。与之相对，在EM树种丰富的区域（如东南亚），复杂的植物-土壤反馈会促使物种维持分化性状，无任何物种具备形成单优群落所需的性状。对婆罗洲与秘鲁亚马逊的植物性状数据开展的分析并未得出明确结论。总体而言，本研究凸显了地理比较法在解析性状趋同与群落趋同之间关系时的应用价值。