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.
