A METAPOPULATION PERSPECTIVE IN PLANT-POPULATION BIOLOGY

1 A metapopulation approach considers the ecology and genetics of popu lations as a product of local dynamics and the regional processes of m igration, extinction and colonization. While conventional metapopulati on theory involves species with frequent population turnover, limited migration and random extinction, it is likely that metapopulation dyna mics, broadly defined as the product of local population dynamics and dispersal, is a feature of all species. 2 Theoretical metapopulation m odels of single species make three critical insights. First, metapopul ations will consist of a shifting mosaic of local populations linked t hrough migration with only a fraction of the available habitat patches occupied at one time. Secondly, there is a threshold number of habita ts available, below which the species cannot persist because extinctio n exceeds colonization. Thirdly, the antagonism between selective forc es acting during recolonization and population growth can influence th e evolution of phenotypic traits. Unfortunately, little empirical data is available to evaluate these ideas for plants or to address the bro ader issue of whether processes at a regional scale add anything to ou r understanding of population dynamics. 3 Plants may seem particularly appropriate for metapopulation analyses as a result of their immobili ty, strong spatial structure and restricted dispersal. However, a revi ew of the literature revealed a paucity of studies that explicitly ado pted a metapopulation approach, particularly in terms of testing theor etical models. We argue that this is because of the difficulty of meas uring parameters such as extinction, colonization and migration that a re central to most metapopulation models. 4 Plants possess a number of special features that present both challenges and opportunities for t he development of new insights into the biology of metapopulations. Th ree particular characteristics, seed dormancy, restricted dispersal an d local adaptation, need to be incorporated into existing theoretical models so they more accurately reflect the dynamics of plant metapopul ations. Finally, more effort is needed to incorporate the explicit spa tial structure of individuals within metapopulations and to investigat e the effect that dispersion has on their growth and reproduction.