A metapopulation perspective in plant population biology

1 A metapopulation approach considers the ecology and genetics of populations as a product of local dynamics and the regional processes of migration, extinction and colonization. While conventional metapopulation theory involves species with frequent population turnover, limited migration and random extinction, it is likely that metapopulation dynamics, broadly defined as the product of local population dynamics and dispersal, is a feature of all species. 2 Theoretical metapopulation models of single species make three critical insights. First, metapopulations will consist of a shifting mosaic of local populations linked through migration with only a fraction of the available habitat patches occupied at one time. Secondly, there is a threshold number of habitats available, below which the species cannot persist because extinction exceeds colonization. Thirdly, the antagonism between selective forces acting during recolonization and population growth can influence the evolution of phenotypic traits. Unfortunately, little empirical data is available to evaluate these ideas for plants or to address the broader issue of whether processes at a regional scale add anything to our understanding of population dynamics. 3 Plants may seem particularly appropriate for metapopulation analyses as a result of their immobility, strong spatial structure and restricted dispersal. However, a review of the literature revealed a paucity of studies that explicitly adopted a metapopulation approach, particularly in terms of testing theoretical models. We argue that this is because of the difficulty of measuring parameters such as extinction, colonization and migration that are central to most metapopulation models. 4 Plants possess a number of special features that present both challenges and opportunities for the development of new insights into the biology of metapopulations. Three particular characteristics, seed dormancy, restricted dispersal and local adaptation, need to be incorporated into existing theoretical models so they more accurately reflect the dynamics of plant metapopulations. Finally, more effort is needed to incorporate the explicit spatial structure of individuals within metapopulations and to investigate the effect that dispersion has on their growth and reproduction.