Data from: Habitat filtering determines the functional niche occupancy of plant communities worldwide

How the patterns of niche occupancy vary from species-poor to species-rich communities is a fundamental question in ecology that has a central bearing on the processes that drive patterns of biodiversity. As species richness increases, habitat filtering should constrain the expansion of total niche volume, while limiting similarity should restrict the degree of niche overlap between species. Here, by explicitly incorporating intraspecific trait variability, we investigate the relationship between functional niche occupancy and species richness at the global scale. We assembled 21 datasets worldwide, spanning tropical to temperate biomes and consisting of 313 plant communities representing different growth forms. We quantified three key niche occupancy components (the total functional volume, the functional overlap between species and the average functional volume per species) for each community, related each component to species richness, and compared each component to the null expectations. As species richness increased, communities were more functionally diverse (an increase in total functional volume), and species overlapped more within the community (an increase in functional overlap) but did not more finely divide the functional space (no decline in average functional volume). Null model analyses provided evidence for habitat filtering (smaller total functional volume than expectation), but not for limiting similarity (larger functional overlap and larger average functional volume than expectation) as a process driving the pattern of functional niche occupancy. Synthesis. Habitat filtering is a widespread process driving the pattern of functional niche occupancy across plant communities and coexisting species tend to be more functionally similar rather than more functionally specialized. Our results indicate that including intraspecific trait variability will contribute to a better understanding of the processes driving patterns of functional niche occupancy.生态位占用（niche occupancy）模式如何从物种贫乏群落到物种丰富群落发生转变，是生态学领域的核心科学问题之一，其与驱动生物多样性格局形成的过程密切相关。随着物种丰富度提升，生境过滤（habitat filtering）应会限制总生态位体积的扩张，而限制相似性（limiting similarity）则会抑制物种间的生态位重叠程度。本研究通过明确纳入种内性状变异（intraspecific trait variability），在全球尺度下探究功能生态位占用（functional niche occupancy）与物种丰富度之间的关联。我们整合了全球范围内的21项数据集，覆盖从热带到温带的各类生物群系（biomes），包含313个代表不同生长型（growth forms）的植物群落。我们为每个群落量化了3项核心生态位占用指标：总功能体积（functional volume）、物种间功能重叠度以及单物种平均功能体积；将每项指标与物种丰富度建立关联，并将其与零假设期望（null expectations）进行对比。随着物种丰富度提升，群落的功能多样性随之升高（总功能体积增加），群落内物种间的功能重叠度也有所上升，但并未对功能空间（functional space）进行更精细的划分（单物种平均功能体积未出现下降）。零模型分析（null model analyses）结果支持生境过滤作为驱动功能生态位占用格局的过程（总功能体积低于预期值），但并未发现限制相似性起到类似作用（功能重叠度与单物种平均功能体积均高于预期值）。综合结论：生境过滤是驱动全球植物群落功能生态位占用格局的普遍过程，共存物种往往表现出更高的功能相似性，而非更强的功能特化（functionally specialized）。本研究结果表明，纳入种内性状变异有助于更深入地理解驱动功能生态位占用格局的生态学过程。