The efficacy of dispersal in relation to safe site area and seed production.

A model is developed to define the efficacy of dispersal in relation to safe site area and seed production. Efficacy is measured as the expected number of progeny from one parent. It is shown that maximization of efficacy does not depend on the density of safe sites. When safe sites are confined to a restricted area around the parent, and safe sites are small or few propagules are produced, dispersal curves with short tails are most efficacious; when safe sites are larger or when more propagules are produced, distributions with longer tails become more advantageous.