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）日益被证实会影响大型植物属的基因库，但该现象极少被用于解释近缘植物物种为何无法同域共存。本研究聚焦澳大利亚维多利亚州格兰扁斯国家公园内的桉属（Eucalyptus）物种，探究环境条件与杂交倾向如何影响物种的邻域同域共存模式。研究人员基于叶绿体DNA（chloroplast DNA）JLA+区域与核糖体DNA（nuclear ribosomal DNA）内部转录间隔区（internal transcribed spacer region）的系统发育不一致程度、基因共享的地理分布模式，以及野外观察到的中间形态表型，筛选出经历持续杂交与渐渗的物种对。研究沿环境梯度布设样地，对物种同域共存情况、功能性状数据（比叶面积[specific leaf area, SLA]、最大株高与种子质量）及环境数据进行采集。整体而言，性状与生境相似性对物种同域共存的影响最为显著（例如，同域共存的物种具有相似的比叶面积）。生殖兼容物种是例外：尽管功能性状相似，它们却极少同域共存。生殖兼容性对同域共存的负效应强于比叶面积的正效应。本研究结果凸显了环境的主导作用，以及进化在塑造本地群落组合中的重要性。我们认为，该系统中阻止近缘物种同域共存的机制是生殖干扰（reproductive interference）而非竞争排除（competitive exclusion）。生殖干扰应被更广泛地视为导致系统发育过度离散（phylogenetic overdispersion）的潜在诱因。