Data from: The roles of ecological and evolutionary processes in plant community assembly: the environment, hybridization and introgression influence co-occurrence of Eucalyptus

Introgressive hybridization is increasingly recognized as having influenced the gene pools of large genera of plants, yet it is rarely invoked as an explanation for why closely related plant species do not co-occur. Here, we asked how the environment and tendency to interbreed relate to neighborhood co-occurrence patterns for Eucalyptus species in the Grampians National Park, Victoria, Australia. We identified species pairs that have experienced ongoing hybridization and introgression on the basis of the extent of incongruence between chloroplast DNA (JLA+ region) and nuclear ribosomal DNA (internal transcribed spacer region) phylogenies, geographic patterns of gene sharing, and field observation of intermediate morphologies. Co-occurrence, trait data (specific leaf area [SLA], maximum height, and seed mass), and environmental data were measured in plots distributed along environmental gradients. Trait and habitat similarity influenced species co-occurrence the most overall (e.g., co-occurring species had similar SLA). Reproductively compatible species were an exception; they rarely co-occurred despite being functionally similar. The negative effect of reproductive compatibility was stronger than the positive effect of SLA on co-occurrence. Our results emphasize the dominant roles of the environment and the importance of evolution in structuring local assemblages. We argue that the mechanism responsible for preventing closely related species from co-occurring in this system is reproductive interference rather than competitive exclusion. Reproductive interference should be considered more generally as a potential cause of phylogenetic overdispersion.渐渗杂交（introgressive hybridization）日益被证实会对大型植物属的基因库造成影响，但极少有研究将其作为解释亲缘关系密切的植物物种为何无法共存的机制。本研究以澳大利亚维多利亚州格兰扁国家公园的桉属（Eucalyptus）物种为研究对象，探究环境条件与杂交倾向如何影响其邻域共存格局。我们基于叶绿体DNA（chloroplast DNA）的JLA+区域与核核糖体DNA（nuclear ribosomal DNA）的内部转录间隔区（internal transcribed spacer region）系统发育树之间的不一致程度、基因共享的地理分布模式，以及野外观测到的中间形态个体，鉴定出了经历持续杂交与渐渗过程的物种对。研究沿环境梯度布设样地，对物种共存情况、功能性状数据（比叶面积（specific leaf area, SLA）、最大株高与种子质量）以及环境数据进行了测定。总体而言，性状与生境相似性对物种共存的影响最为显著——例如，共存物种的比叶面积较为相近。但生殖兼容的物种是个例外：尽管功能性状相似，这类物种却极少共存。生殖兼容性对物种共存的负面影响强度，超过了比叶面积对共存的正面影响。本研究结果凸显了环境因素的主导作用，以及演化过程在构建局域群落结构中的重要性。我们提出，在本研究系统中，阻止亲缘密切物种共存的核心机制是生殖干扰而非竞争排斥。生殖干扰应被更广泛地视作引发系统发育过分散（phylogenetic overdispersion）的潜在诱因。