Box 1 How does dispersal evolve?
The evolutionary ecology of dispersal [News and Comment]
Ulf Dieckmann, Bob O'Hara and Wolfgang Weisser
Trends in Ecology & Evolution, 1999, 14:3:88-90



In the past 30 years, several mechanisms have been identified that influence the evolution of dispersal strategies. Mathematical models designed to investigate the evolution of dispersal usually assume that local populations occur in discrete habitats, and that in each generation a certain fraction of individuals disperses from natal habitats. Most models are based on game theory and seek to delineate evolutionarily stable strategies^5,6.

Habitat extinction risks^7,8 ('unstable habitats'): risks of local extinction are the most intuitive reason for why dispersal evolved and thus have been tested repeatedly in the field, using, for example, wing-dimorphic insects⁹.

Competition among kin¹⁰: dispersal is selected for if it reduces competition between close relatives, even in the absence of other dispersal-promoting factors, such as unstable habitats.

Temporal and spatial variability in habitat quality^11,12: in general, spatial variability selects against and temporal variability selects for dispersal. If habitats fluctuate both spatially and temporally, the optimal dispersal rate depends on how fluctuations are correlated. A possible source of variability is chaotic population dynamics¹³.

Costs of dispersal¹⁰: if dispersal is costly (e.g. because of mortality risks during travelling or investments into dispersal morphology), optimal dispersal rates are decreased.

Inbreeding¹⁴: costs of inbreeding can also select for dispersal, and is independent of competition between related individuals.