Growing concerns over the persistence of threatened and endangered species have rekindled interest in one of the classic problems in ecology: how do rare species persist? Without large populations distributed across heterogeneous environments, rare species are traditionally regarded as susceptible to extinction from environmental variability. By contrast, numerous coexistence models suggest that for species with dormancy, environmental fluctuations may be essential for persistence in competitive communities. Variable germination and dormancy allow species to exploit temporal variation to avoid both unfavorable environments and intense competition. Despite acceptance among community ecologists that environmental fluctuations may favor coexistence via these "storage effect" mechanisms, their implications for understanding how rare plants persist are only beginning to be explored. Better understanding how dormancy, surrounding community dynamics, and environmental variation influence persistence is essential to successfully managing threatened populations. This proposal outlines research to examine how rare annual plants persist in the highly variable, exotic grass dominated habitats of the California Channel Islands. With tenfold annual variation in rainfall, and over 15 rare and endangered annual plants, the island system provides a unique opportunity to examine how germination biology, environmental variation, and surrounding community dynamics influence persistence. The research team brings together a theoretical ecologist specializing in annual plant population models, a field ecologist with experience studying biological invasions in California herbaceous systems, and a conservation practitioner working in the Channel Islands National Park. The intellectual merit of the proposed research is that it will clarify how dormancy, environmental variation and surrounding community dynamics influence the persistence of rare annual plants. This is particularly important considering the increased environmental variation forecasted with climate change, and the continuing invasion of exotic species. The broader implications include the training of postdoctoral, graduate, and undergraduate students to work at the interface of models and experiments, and the generation of data necessary for successfully managing the rare annual plants of the Channel Islands. Through collaborations with the National Park Service and Nature Conservancy, the results of this project will be communicated to the general public and those directly responsible for managing the unique island flora.