Many sexual-asexual complexes show a distinct pattern where the asexuals have larger and more northerly ranges than closely related sexuals. A prime candidate to explain this so-called "geographical parthenogenesis" is ecological niche divergence between the sexuals and asexuals. Modern niche modelling techniques allow testing niche divergence by directly comparing the niches of sexuals and asexuals. In this study, I use such techniques to perform range-wide tests of whether nine bioclimatic variables, including annual mean temperature and annual precipitation, contribute to geographical parthenogenesis in two dandelion taxa: Taraxacum section Ruderalia and Taraxacum section Erythrosperma, which are both comprised of sexual diploids and asexual triploids. For both sections, I found evidence of niche divergence, though the exact nature of this divergence was different for the two sections. In section Ruderalia, the sexuals preferred warmer and wetter conditions, whereas in section Erythrosperma, the sexuals preferred dryer conditions. Using Species Distribution Modelling, consistent differences between the sexuals and asexuals were found when looking at the niche determinants: the variables that are most important for modelling the distribution. Furthermore, and in contrast with theoretical expectations that predict that the sexuals should have a wider niche, in section Erythrosperma the asexuals were found to have a wider niche than the sexuals. In conclusion, differences in niche optima, niche determinants, and niche width all contribute to the pattern of geographical parthenogenesis of these two dandelion taxa. However, the results also indicate that the exact causation of geographical parthenogenesis is not uniform across taxa.

中文翻译：

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生态位分歧有助于两个蒲公英类群的地理孤雌生殖。

许多性-无性恋复合体显示出一种独特的模式，其中无性恋者的范围比密切相关的性恋者更大，更北。解释这种所谓的“地理孤雌生殖”的主要候选者是有性和无性之间的生态位差异。现代利基建模技术允许通过直接比较有性和无性的利基来测试利基差异。在这项研究中，我使用这些技术对包括年平均温度和年降水量在内的九个生物气候变量是否有助于两个蒲公英类群的地理孤雌生殖进行了范围广泛的测试：蒲公英部分 Ruderalia 和蒲公英部分 Erythrosperma，它们都由有性二倍体和无性三倍体。对于这两个部分，我发现了利基差异的证据，尽管这两个部分的这种分歧的确切性质是不同的。在 Ruderalia 部分，有性昆虫喜欢温暖和潮湿的环境，而在 Erythrosperma 部分，有性动物喜欢干燥的环境。使用物种分布建模，在查看生态位决定因素时发现了有性和无性之间的一致差异：对分布建模最重要的变量。此外，与预测有性动物应该具有更广泛生态位的理论预期相反，在红皮科部分，发现无性动物比有性动物具有更广泛的生态位。总之，生态位最优、生态位决定因素和生态位宽度的差异都有助于这两个蒲公英类群的地理孤雌生殖模式。然而，