Collaborative Research: Extinction Dynamics and Population Bottlenecks in an Annual Plant with Seed Bank

许多生物生活在生态条件每年波动很大的环境中。在某些年份，环境条件可能是良好的，因此为人口增长提供了有利的条件，而在其他年份，环境条件可能是不利的，因此导致人口增长率下降。由于在某些年份迫使一个种群的规模变得非常小，这种变异将增加种群灭绝的可能性，并促进遗传变异的丧失。生活在长期变化环境中的物种往往具有适应能力，可以缓冲这些环境变化的有害影响。拟议中的研究将测试其中一种适应性的有效性，即一年生植物的土壤种子库。种子库是指储存在土壤中的休眠、有活力的种子。由于一年内生产的所有种子都不会在下一个生长季节发芽，种子库创造了年龄结构，有效地将再生努力（因此灭绝的风险）分散到多年。将进行两项研究。首先，将建立实验种子库，以评估种子库中萌发的种子在五年内的人口统计学和遗传动力学。在另一项研究中，研究人员将建立多个重复种群，通过实验让一半的成年种群灭绝，而让另一半不受操纵。人口统计学和遗传动力学将在五年内对这些实验人群进行量化。从这两项研究中，将构建对大环境扰动的遗传和人口后果的完整描述。本研究是对种子库对自然植物种群的人口统计和进化过程影响的首次实证评估之一。本研究的结果将对种子库效应的未来理论发展以及对生活在长期变化和不可预测环境中的稀有和濒危物种（包括植物和动物）的保护具有重要意义。

9421605 McPEEK Many organisms inhabit environments in which ecological conditions fluctuate greatly from year to year. In some years environmental conditions may be benign and therefore foster favorable conditions for population growth, while conditions in other years may be inhospitable and consequently result in declining population growth rates. By forcing a population to very small sizes in some years, such variability will heighten the chances of total population extinction and promote the loss of genetic variation. Species inhabiting chronically variable environments often possess adaptations which should buffer these detrimental effects of environmental variability. The proposed research will test the effectiveness of one of these adaptations, the soil seed bank of annual plants. Seed banks are the presence of dormant, viable seeds stored in the soil. Since all seeds produced in one year do not germinate in the following growing season, seed banks create age structure which effectively spreads the regenerative effort (and thus the risk of extinction) over multiple years. Two studies will be performed. In one, experimental seed banks will be constructed to evaluate the demographic and genetic dynamics of seeds germinating from the seed bank over five years. In the other study, the investigators will establish multiple replicate populations, experimentally impose adult extinction on half, and leave the other half unmanipulated. The demographic and genetic dynamics will be quantified for these experimental populations over five years. From these two studies a complete description of the genetic and demographic consequences of large environmental perturbations will be constructed. This research represents one of the first empirical evaluations of the effects of seed banks on the demographic and evolutionary processes in natural plant populations. The results of this study will have important implications for future theoretical development of the effects of seed banks an d for the conservation of rare and endangered species, both plants and animals, living in chronically variable and unpredictable environments.