THE NAME OF THE ROSE: A REVIEW OF IDEAS ON THE EUROPEAN BIAS IN ANGIOSPERM CLASSIFICATION

SPECIES RICHNESS WITHIN FAMILIES OF FLOWERING PLANTS

Variation in species and genus richness among families of flowering plants was examined with respect to four classification variables: geographical distribution, growth form, pollination mode, and dispersal mode. Previous studies have estimated rates of species proliferation from age and contemporary diversity. Here we found that the earliest appearances in the fossil record are correlated with contemporary familial species richness, abundance in the fossil record, and the independent variables considered in this analysis. Thus, we believe that the fossil record does not provide reasonable estimates of the ages of families and that the rate of species proliferation cannot be calculated from such data without bias. Accordingly, our subsequent analyses were based on contemporary species richness of families. Although the classification variables were interrelated, each made largely independent contributions to familial species richness. Cosmopolitan families were 5.6 times more species-rich than strictly tropical families and 35 times more species-rich than strictly temperate families. Families including both herbaceous and woody growth forms were 5.7 and 14 times more species-rich than families with either growth form alone. Although animal pollination was significantly associated with elevated familial species richness, the effect was statistically weak. The most prominent effect was that families with both abiotic and biotic dispersal had more than 10 times as many species as families with either dispersal mode alone. Our analyses also revealed that families having both dispersal modes were more likely to have several growth forms, suggesting that evolutionary flexibility of morphology may be generalized over diverse aspects of life history. These results do not support the idea that pollination and dispersal by animals were primarily responsible for the tremendous proliferation of angiosperm species, either by producing population structures conducive to speciation or by applying selection for diversification. Instead, the importance of varied dispersal mode, growth form, and climate zone in predicting high familial species richness suggests that a capacity to diversify morphologically and physiologically may have been primarily responsible for high rates of species proliferation in the flowering plants.

On the size distribution of live genera

This article deals with the theoretical size (number of species) distribution of live genera, arising from a simple model of macroevolution in which speciations and extinctions are assumed to occur independently and at random, and in which new genera are formed by the random splitting of existing genera. Mathematically, the distribution is that of the state of a homogeneous birth-and-death process after an exponentially distributed time. An ordinary differential equation for the generating function of the distribution is derived and solved and a recurrence relation for computing the probabilities in the distribution presented. Some properties of the distribution, including asymptotic behaviour, are examined and the distribution of the time since establishment of a genus of a given size derived. Fitting the distribution to empirical taxon size distributions by maximum likelihood is discussed and two examples are presented.

Self-similarity in biological classifications

Size distributions of supraspecific taxa, e.g. genera, measured as the number of included subtaxa, e.g. species, are found to follow a power law. This behaviour has been verified for a number of taxa of different size and taxonomic rank, thus suggesting a fractal structure of biological classifications. This is regarded as probably dependent on evolutionary processes shaping the phylogenetic tree, especially speciation and extinction, as well as on the topological properties of developmental constraints and/or of the ecospace(s) with which the group has been confronted during its history. The role of taxonomic bias is deemphasized.