This research will investigate the dynamics of Sonoran Desert annual plants in order to determine how these plants adapt to unpredictable environments. Desert annuals have been used to study community dynamics in highly variable environments yet the dynamics of seed germination and dispersal, considered primary determinants of persistence and coexistence are not well known. This research will continue and extend a 12 year data set on the population and community dynamics of desert winter annual plants at the Desert Laboratory of the University of Arizona (formerly the Carnegie Desert Research Laboratory founded and in continuous operation since 1903). Since the production of long-lived dormant seeds is considered to be an important feature permitting desert annuals to persist though unfavorable conditions they will determine the fraction of seeds the seed bank germinating each year and construct depletion curves for both natural and experimental seed banks in the field. Also, field experiments will be conducted to measure seed dispersal distances. Field and laboratory germina tion experiments will describe seed dormancy mechanisms. Finally, species responses to weather variation will be constructed and used in computer simulations of the evolution of dormancy and dispersal and variance-mediated species coexistence. Understanding the dynamics of desert annuals will improve our knowledge of desert ecosystems, since annuals represent a major and highly variable component of primary productivity on which the desert animals depend. Deserts worldwide are undergoing shifts in geographic boundaries. Since annual plants respond quickly to weather shifts, the long-term monitoring of desert annuals should also provide a unique assessment of the biotic impacts of global warming and climate change.
