Heard Stephen B
Department of Biology, Leidy Labs, University of Pennsylvania, Philadelphia, PA, 19104-6018, USA.
Evolution. 1992 Dec;46(6):1818-1826. doi: 10.1111/j.1558-5646.1992.tb01171.x.
I examine patterns in tree balance for a sample of 208 cladograms and phenograms from the recent literature. I provide an expression for expected imbalance under a simple, uniform-rate random speciation model, and I estimate variances by simulation for the same model. Imbalance decreases with tree size (number of included taxa) in both theoretical and literature trees. In contrast to previous suggestions, I find cladistic trees to be no more imbalanced than phenetic trees when confounding variables are appropriately controlled. The degree of imbalance found in literature trees is inconsistent with the uniform-rate speciation model; this is most likely a result of variability in speciation and extinction rates among real lineages. The existence of such variation is a necessary (but not sufficient) condition for the operation of the macroevolutionary processes of species sorting and species selection.
我研究了近期文献中208个分支图和表型图样本的树形平衡模式。我给出了一个简单的、均匀速率随机物种形成模型下预期不平衡的表达式，并通过模拟估计了同一模型的方差。在理论树和文献树中，不平衡程度都随着树的大小（包含的分类单元数量）而降低。与之前的观点相反，我发现当混杂变量得到适当控制时，分支树并不比表型树更不平衡。文献树中发现的不平衡程度与均匀速率物种形成模型不一致；这很可能是实际谱系中物种形成和灭绝速率变化的结果。这种变化的存在是物种分类和物种选择宏观进化过程运作的必要（但不充分）条件。
