Modern and Cretaceous-Cenozoic diversification of angiosperms
V. L. Komarov Botanical Institute, RAS
197376 St.-Petersburg, Prof. Popova, 2
e-mail: sn.sheremetiev@gmail.com
Cretaceous-Cenozoic history of angiosperms resulted in emergence of certain distribution of taxa belonging to different ranks (numbers of species and genera within a family, S/G-ratio in families, numbers of species within a genus). In most cases, such distributions can be satisfactorily described by power law (Pareto distribution). In logarithmic coordinates, the power function looks like a straight line. Empirical curves coincide with this line fairly well except that in the right part of the scatters, i.e., in the region of small-sized taxa, empirical curves markedly deviate from theoretical ones. This means that small-sized taxa should be considerably larger to fit the theoretical curves properly. By modeling the S/G-ratio in families it is shown that in the wide range of iteration observed and calculated numbers of species correspond satisfactory only when dynamic factor of extinction is applied. So, the assumption is made about differentiated species extinction in course of angiosperms evolution meaning that in genera with large number of species the rate of extinction should be minimal. On the opposite, with species numbers lessening the extinction rate might increase by the orders of magnitude. As a result, large genera were becoming even larger, while small genera - even smaller. At that, frequency distribution of species within genera corresponded to the power law. Initial divergence of taxa, which has led to their further dividing into large and small ones, could be caused by appearance and expansion of herbs with their functional and adaptive potential.
