Extinction and Conservation Biology of Land Plants

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To improve our understanding on biology of endangered plant species, a series of studies described below have been carried out.(1) Populations of plant species occurring in river banks are often maintained under frequent natural disturbance such as flooding. Some of those species are now endangered due to stabillization of habitat environment under human control. To predict the fates of those species, simulation models assuming lattice structure were developed. Some critical parameters empoyed in the models were estimated from demographic studies for Aster kantoensis. Sensitivity and elastisity analyzes are now in progress to evaluate relative contributions of the parameters to risk of extinction.(2) Genetic variations of endangered species were estimated using allozyme and DNA merkers. In Arisaema and Eupatorium japonicum, there were very limited amounts of genetic variations, suggesting that restricted genetic variance might constrain adaptatin to environmental changes. On the other hand, Aster kantoensis had a high level of genetic variation, suggesting that effective population size is still sufficiently large to maintain genetic variation. Further annual census of genetic variation in A.kantoensis will be usuful to follow changes in effective population size of this endangered species.To elucidate processes of extinction in the past, a new method to estimate a turn-over rate of species from a molecular phylogenetic tree was developed.