CONTRIBUTIONS OF INDIVIDUAL TAXA TO OVERALL MORPHOLOGICAL DISPARITY
CONTRIBUTIONS OF INDIVIDUAL TAXA TO OVERALL MORPHOLOGICAL DISPARITY
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DOI：
10.1017/s0094837300014056
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发表时间：
1993-09-01
期刊：
影响因子：
2.7
通讯作者：
FOOTE, M
中科院分区：
文献类型：
--
作者：
FOOTE, M
两种方法进行了讨论，以评估的贡献子群的形态差异较大的一组包含它们。(1)给定在形态空间中代表标本或物种的点的排序，整个组的形态差异被测量为点到质心的平均平方距离。子组对形态差异的贡献是以其点与总体质心（而不是子组质心）的平均平方距离来衡量的，通过相对于总组样本量的子组样本量进行加权。因此，一个组的形态视差可以被添加到它的子组的视差分量，并且这些子组的相对贡献可以被定量地评估。(2)另一种方法是比较一个组的形态差异，如果忽略某个子组，它将有差异。如果所得视差与原始视差显著不同，则认为所讨论的子组对形态视差具有显著影响。由于某些亚群在形态空间中非常集中，当差异被测量为物种之间的平均差异时，省略它们会导致形态差异的增加。在一般情况下，相对较大的亚组，位于外围的形态空间作出最大的贡献形态差异，和失败的样本较小的群体往往有差距估计的影响不大。这两种方法适用于形态差异三叶虫，划分在不同层次的分类层次。这两种方法的结果直观合理，基本一致，并指出早寒武世olenelloids，寒武-奥陶纪Libristoma，奥陶纪Asaphina和Cheirurina，志留纪-泥盆纪Phacopida和Phacopina，泥盆纪Proetida的优势。
Two methods are discussed for assessing the contributions of subgroups to the morphological disparity of the larger group containing them. (1) Given an ordination of points representing specimens or species in morphological space, morphological disparity of the entire group is measured as the average squared distance of points from the centroid. The contribution that a subgroup makes to morphological disparity is measured as the average squared distance of its points from the overall centroid (not the subgroup centroid), weighted by the subgroup sample size relative to the total group sample size. Thus, morphological disparity of a group can be additively partitioned into the disparity components of its subgroups, and the relative contributions of these subgroups can be assessed quantitatively. (2) An alternative approach is to compare morphological disparity of a group to the disparity it would have if a certain subgroup were omitted. If the resulting disparity differs substantially from the original disparity, then the subgroup in question is considered to have a significant effect on morphological disparity. Because some subgroups are very centralized in morphological space, omitting them can cause an increase in morphological disparity when disparity is measured as the average dissimilarity among species. In general, relatively large subgroups that are located peripherally in morphospace make the greatest contributions to morphological disparity, and failure to sample smaller groups often has little effect on disparity estimates. The two methods are applied to morphological disparity in trilobites, partitioned at different levels in the taxonomic hierarchy. Results of the two methods are intuitively reasonable and largely in agreement, and point to the predominance of Early Cambrian olenelloids, Cambro-Ordovician Libristoma, Ordovician Asaphina and Cheirurina, Siluro-Devonian Phacopida and Phacopina, and Devonian Proetida.