Advantages of seed dispersal: A re-evaluation of directed dispersal

Seed dispersal can be advantageous (1) in escape from densityor distance-dependent seed and seedling mortality, (2) by colonization of suitable sites unpredictable in space and time, and (3) by directed dispersal to particular sites with a relatively high probability of survival. Most previous research on the consequences of seed dispersal has focused on escape and colonization because adaptations ensuring directed dispersal are not expected under the paradigm of diffuse mutualism that characterizes the modern view of seed dispersal evolution. In this paper, I suggest that directed dispersal is more common than previously believed even in the absence of plant adaptations to promote it. Directed dispersal may be seen in particular among animaldispersed plants and in arid ecosystems or successional areas, but has been overlooked due to the lack of detailed data on seed shadows generated by particular species, and the fact that the alternative advantages of dispersal are not mutually exclusive. Although directed dispersal is never thought to be the only advantage of dispersal, it may often be ecologically important if one dispersal vector has a disproportionate effect on plant recruitment. Furthermore, in human-disturbed and managed ecosystems, directed dispersal may be important in restoration. More studies detailing the consequences of different patterns of seed dispersal will be useful for conservation and management strategies.