Opposing community assembly patterns for dominant and non-dominant plant species in herbaceous ecosystems globally

Biotic and abiotic factors interact with dominant plants —the locally most frequent or with the largest coverage— and non-dominant plants differently, partially because dominant plants modify the environment where non-dominant plants grow. For instance, if dominant plants compete strongly, they will deplete most resources, forcing non-dominant plants into a narrower niche space. Conversely, if dominant plants are constrained by the environment, they might not exhaust available resources but instead may ameliorate environmental stressors that usually limit non-dominants. Hence, the nature of interactions among non-dominant species could be modified by dominant species. Furthermore, these differences could translate into a disparity in the phylogenetic relatedness among dominants compared to the relatedness among non-dominants. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (e.g., co-dominant grasses), suggesting dominant species are likely organized by environmental filtering, and that non-dominant species were either randomly assembled or overdispersed. Traits showed similar trends for those sites (

生物因子与非生物因子（biotic and abiotic factors）与优势植物（dominant plants）——即当地出现频率最高或盖度最大的物种——以及非优势植物（non-dominant plants）的互作模式存在差异，部分原因在于优势植物会改变非优势植物的生长环境。
例如，若优势植物竞争能力极强，则会耗尽绝大多数资源，迫使非优势植物的生态位空间（niche space）变窄。反之，若优势植物受环境约束，其未必会耗尽可用资源，反而可能缓解通常会限制非优势植物生长的环境胁迫因子。
因此，优势物种可能会改变非优势物种间的互作本质。此外，这些差异还可能导致优势类群间的系统发育亲缘关系（phylogenetic relatedness）与非优势类群间的亲缘关系存在差异。
本研究通过对全球五大洲的78片草原开展系统发育离散度（phylogenetic dispersion）分析，结果发现优势物种呈现聚簇现象（如共优势禾本科植物），表明优势类群大概率由环境过滤（environmental filtering）作用所塑造；而非优势物种的群落组装则呈现随机分布或系统发育离散的模式。上述样地的功能性状也呈现出相似的趋势（