BACKGROUND AND AIMS Heterospecific pollen transfer may reduce fitness of recipient species, a phenomenon known as reproductive interference. A theoretical study has predicted that distributions of species pairs affected by reproductive interference may be syntopic under negligible reproductive interference, sympatric but with partitioning at small spatial scale (i.e., allotopic) under weak interference, or exclusive, when reproductive interference is strong. Verifying these predictions is essential for evaluation of the applicability of reproductive interference as a general assembly rule of biological communities. The aim of this study was to test these predictions in two sympatrically distributed wild Geranium species, G.thunbergii and G. wilfordii. METHODS To measure the effect of reproductive interference, the association between the relative abundance of the counterpart species and seed set in the focal species, and seed set reduction following the mixed pollination, were analysed. The possibility of hybridization with viable offspring was examined by genotyping plants in the field and after mixed pollination. Fertility of putative hybrids was based on their seed set and the proportion of pollen grains with apertural protrusions. A transect study was conducted to examine spatial partitioning, and possible influences of environmental conditions (canopy openness and soil moisture content) on partitioning between the species were analysed. KEY RESULTS Neither abundance of the counterpart species nor heterospecific pollen deposition significantly affected seed set in the focal species, and hybridization between species was almost symmetric. Putative hybrids had low fertility. The two species were exclusively distributed at small scale, although environmental conditions were not significantly different between them. CONCLUSIONS The allotopy of the two species may be maintained by relatively weak reproductive interference through bidirectional hybridization. Re-evaluation of hybridization may allow ongoing or past reproductive interference to be recognized and provide insight into the distributional relationships between the interacting plants.

中文翻译：

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通过生殖干扰在本地天竺葵物种中划分栖息地

背景和目的 异种花粉转移可能会降低受体物种的适应性，这种现象称为生殖干扰。一项理论研究预测，受生殖干扰影响的物种对的分布在可忽略的生殖干扰下可能是同域的，在弱干扰下同域但在小空间尺度（即同位异位）分区，或在生殖干扰强时排他。验证这些预测对于评估生殖干扰作为生物群落大会规则的适用性至关重要。本研究的目的是在两个同域分布的野生天竺葵物种 G.thunbergii 和 G. wilfordii 中测试这些预测。方法 测量生殖干扰的影响，分析了对应物种的相对丰度与焦点物种中的结实率与混合授粉后结实率降低之间的关联。通过在田间和混合授粉后对植物进行基因分型来检查与有活力的后代杂交的可能性。假定杂交种的生育力是基于它们的种子集和具有孔突的花粉粒的比例。进行了横断面研究以检查空间分区，并分析了环境条件（冠层开度和土壤水分含量）对物种之间分区的可能影响。主要结果 对应物种的丰度和异种花粉沉积均不显着影响焦点物种的结实，物种之间的杂交几乎是对称的。假定的杂交种生育力低。这两个物种仅以小规模分布，尽管它们之间的环境条件没有显着差异。结论通过双向杂交相对较弱的繁殖干扰，可以维持两个物种的同种异体。重新评估杂交可能允许识别正在进行或过去的生殖干扰，并提供对相互作用植物之间分布关系的洞察。