LIKELIHOOD AND PARSIMONY: COMPARISON OF CRITERIA AND SOLUTIONS

Abstract— The merits of alternative approaches to the inference of evolutionary trees have been much discussed, but there have been few attempts to compare inferences systematically or to pinpoint the source of differences. The two major classes of approach are via likelihood inference under an evolutionary model and estimates based upon parsimony methods. Within the general class of likelihood approaches, there are differences depending upon the particular class of models considered. This paper makes comparisons of the characteristics of inferences for the case of quantitative variation (of allele frequencies, for example), concentrating on the case of very small numbers of populations where explicit solutions are possible, but also upon features which apply as well to inferences for larger groups of populations. The parsimony method of "minimum evolution" was proposed by Edwards and Cavalli-Sforza (1964) to provide an approximation to the likelihood solution for an intractable model. In fact, its estimated phylogenies are closest to those of a more recent model of Felsenstein (1981) which, like parsimony, produces a fundamentally unrooted tree. Likelihood estimates based upon models involving an implicit or explicit root are radically different. These differ also from each other, depending upon whether or not the root is explicitly estimated, and upon whether or not a model for the fissioning of populations is included. Some general features of the comparisons can be summarized.     

MODELS OF ECOSYSTEMS AND AQUATIC ENVIRONMENTS: DEVELOPMENT AND APPLICATION

SUMMARY

An historical treatment of a number of principal events is given. This leads to an assessment of the current research approach in hydrobiology and its success in the development of process orientated ecosystem component models. With the contemporaneous development of similar models in hydrodynamics it is possible to link the two disciplines into an interactive framework. The recent work in the Hartbeespoort Dam project, Lake le Roux and Burrinjack Reservoir, Western Australia shows how valuable this approach has become, particularly as regards defining, with greater precision, the effects of variation in stability in the uppermixed layer of reservoirs upon the accumulation and dispersion of algal communities.     

被子植物起源和早期演化研究的回顾与展望

近年来,被子植物起源和早期演化研究,由于手段和技术的更新,资料大量积累,取得了许多重要进展,成为植物学领域的一大热点。本文对过去近五十年的研究作了回顾,并从分子系统学、分支系统学、花原基发生的形态学、花发育的分子遗传学及白垩纪花和其它生殖结构化石研究等五个方面对该领域在最近十几年的研究进展进行综述,最后,对今后如何开展这方面的工作作了简要评论。