Extinction and Conservation Biology of Land Plants

为了加深我们对濒危植物生物学的了解，我们进行了一系列的研究。(1)河岸植物种群经常在洪水等频繁的自然干扰下维持。由于人类控制下栖息地环境的稳定，其中一些物种现已濒临灭绝。为了预测这些物种的命运，人们开发了假设晶格结构的模拟模型。模型中的一些关键参数是从关东紫荆的人口统计研究中估计出来的。目前正在进行敏感性和弹性分析，以评估这些参数对灭绝风险的相对贡献。(2)利用等位酶和DNA Merkers估计濒危物种的遗传变异。在天南星和紫茎泽兰中，遗传变异的数量非常有限，这表明受限的遗传变异可能会限制对环境变化的适应。另一方面，关东紫荆具有较高的遗传变异水平，表明有效种群规模仍然足够大，足以维持遗传变异。进一步的年度关东曲柳遗传变异普查将有助于跟踪该濒危物种有效种群规模的变化。为了阐明过去的灭绝过程，开发了一种从分子系统发育树估计物种周转率的新方法。

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.