REU: Dynamics of Tropical Forest Seed Banks: Seed Predatorsas Determinants of Forest Regeneration Patterns and Plant- frugivore Coevolution

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Seed dormancy mechanisms are widespread among tropical plants that colonize small-scale disturbances (e.g., treefalls),and presumably evolved because disperses deposit most seeds in inappropriate habitats (i.e., beneath intact forest canopies). Most colonists indeed arrive before gap formation, but the typical "residence time" of seeds in the soil before gap information is unknown. How long seeds persist in the soil is dependent upon the rates at which they are "removed," both by predators and by exceeding inherent limits of viability. Rates of removal from the soil have profound consequences for such "pioneer" plants and the communities in which they occur: species composition in patches recovering from natural or anthropogenic disturbance is largely determined by the composition of the seed bank at the time of disturbance. In addition, seed removal rates mediate the fitness increments associated with different ripening schedules and with dispersal by different animals. This study will take advantage of extensive background data on germination requirements, seed dormancy, and bird-generated seed shadows in Costa Rican pioneer plants to evaluate these effects. Through several controlled, replicated field experiments, the P.I. will measure rates if seed input to and removal from the soil seed bank, and then examine the consequences of seed demography for community structure and the evolution of ripening phenologies and plant-disperser relationships. This work will have important implications for analyses of tropical forest dynamics.