Distinguishing the roles of dispersal in diversity maintenance and in diversity limitation

In recent years, a considerable research effort has gone into studying how dispersal might affect the diversity of local communities. While this general topic has received attention from theoretical and empirical ecologists alike, the research focus has differed between the two groups; theoretical ecologists have explored the role of dispersal in the maintenance of diversity within local communities, whereas empirical ecologists have sought to quantify the role of dispersal in limiting local diversity. In this paper we argue that, because the underlying causal relationship between dispersal and diversity is empirically unknown (e.g., flat, linear, and humped relationships have been suggested), there is no necessary relationship between the dispersal-maintained and the dispersal-limited component of diversity. In order to test and parameterize theoretical models we therefore need to develop a empirical approaches that allow us to quantify not only the dispersal-limited but also the dispersal-maintained component of diversity