Holman Eric W
Department of Psychology, University of California, Los Angeles, 90095, USA.
Syst Biol. 2005 Dec;54(6):895-9. doi: 10.1080/10635150500354696.
The imbalance of a node in a phylogenetic tree can be defined in terms of the relative numbers of species (or higher taxa) on the branches that originate at the node. Empirically, imbalance also turns out to depend on the absolute total number of species on the branches: in a sample of large trees, nodes with more descendent species tend to be more unbalanced. Subsidiary analyses suggest that this pattern is not a result of errors in tree estimation. Instead, the increase in imbalance with species is consistent with a cumulative effect of differences in diversification rates between branches. [Equal-rates Markov model; imbalance; phylogeny shape; proportional-to-distinguishable-arrangements model.].
系统发育树中一个节点的不平衡可以根据起源于该节点的分支上物种（或更高级分类单元）的相对数量来定义。从经验上看，不平衡还取决于分支上物种的绝对总数：在大树样本中，具有更多后代物种的节点往往更不平衡。辅助分析表明，这种模式不是树估计误差的结果。相反，不平衡随物种数量的增加与分支间多样化速率差异的累积效应是一致的。[等速率马尔可夫模型；不平衡；系统发育形状；比例与可区分排列模型。]
