Department of Biology, University of Missouri-St. Louis, One University Boulevard, St. Louis, MO 63121, USA.
Syst Biol. 2012 Mar;61(2):179-94. doi: 10.1093/sysbio/syr084. Epub 2011 Aug 16.
Species are commonly delimited on the basis of gaps in patterns of morphological variation, but there seems to be little recent work on methods to objectively assess such gaps. Here, we introduce a statistical approach that uses measurements of continuous morphological characters and geographic variation in those characters to (i) measure the strength of the evidence for the existence of a gap in morphological variation between two hypothesized species and (ii) examine if a gap in morphological variation between two hypothesized species can be explained by an alternative hypothesis of geographic variation within a species. This approach is based on recent developments in analyses of multivariate normal mixtures, estimates of multivariate tolerance regions, and principal coordinates of neighboring matrices. We demonstrate the application of the approach by examining previously proposed hypotheses of species limits in the plant genus Escallonia. We discuss the main features of the method, including potential limitations, in relation to other approaches that use gaps in morphological variation as a criterion for species delimitation. The method we propose can help strengthen the link between the theory and practice of species delimitation by increasing the transparency and consistency of taxonomic decisions based on morphology, thus contributing to integrative approaches for species delimitation that consider morphological and geographic data on an equal footing with other kinds of information.
物种通常根据形态变异模式中的间隙来划定界限，但似乎很少有最近关于客观评估这些间隙的方法的研究。在这里，我们介绍了一种统计方法，该方法使用连续形态特征的测量值和这些特征的地理变异来：（i）衡量两个假设物种之间形态变异存在间隙的证据强度；（ii）检查两个假设物种之间形态变异的间隙是否可以用物种内地理变异的替代假设来解释。该方法基于多元正态混合分析、多元容限区域估计和相邻矩阵主坐标的最新进展。我们通过检查植物属 Escallonia 中以前提出的物种界限假设来演示该方法的应用。我们讨论了该方法的主要特点，包括与其他使用形态变异间隙作为物种划分标准的方法相关的潜在局限性。我们提出的方法可以通过增加基于形态学的分类决策的透明度和一致性，从而有助于与形态和地理数据同等对待的综合物种划分方法，来帮助加强物种划分的理论和实践之间的联系。
