Key causes of dispersal:
- Competition dispersal (habitat depletion). This is probably a key
cause of dispersal in plants, as resources such as light, root space, and
nutrients are depleted by the parental plant. In animals it also plays a key
role in many species and recurs as a theme in this outline. Infanticide is
a common response to habitat depletion in rodents and can be thought of as
the result of resource competition. Infanticide is performed by females and
males that are unrelated to or are unfamiliar with the pups (refer back to:
kin recognition) Sherman (1981). in crowded populations of related mice and
voles infanticide is much less likely.
- Inbreeding avoidance. Bollinger et al. found that in meadow voles
animals were more likely to disperse from plots occupied by siblings than
from plots occupied by non siblings. Note that this interpretation, but perhaps
not the actual result, differs from that of Ims and Andreasson, which is discussed
above: Unlike the Lena et al paper on lizards no effort is made to partition
inbreeding avoidance from kin-competition avoidance.
- Kin-competition avoidance. This is really difficult to discriminate
from inbreeding avoidance because the result is essentially the same; close
kin end up not living near one another. Kin-competition avoidance is, I think,
important to consider in the general mix of causes of dispersal. Lena et al.
deal directly with this issue.
- Breeding dispersal. Gravid females may leave social groups or natal
areas to find more appropriate places to give birth and feed their offspring.
The motivation for this overlaps with other causes of dispersal--habitat depletion
could stimulate movement, colonization could be a goal of movement.
- Colonization dispersal. Selection may favor colonization of new
habitats. Individual fitness can be enhanced for plants or animals that find
a vacant habitat patch.
Bollinger, E. K., S. J. Harper and G. W. Barrett 1993. Inbreeding avoidance
increases dispersal movements of the meadow vole. Ecol. 74:1153-1156.
Dobson, F. S. 1985. Multiple causes of dispersal. Am. Nat. 126:855-858.
Lena, J.-P., J. Clobert, M. de Fraipont, J. Lecomte and G. Guyot. 1998. The
relative influence of density and kinship on dispersal in the common lizard.
Behav. Ecol. 9:500-507.
Sherman, P.W. 1981. Reproductive competition and infanticide in Beldingšs ground
squirrels and other animals. In Natural selection and social behavior, Chiron
Press, New York, R. D. Alexander and D. Tinkle, eds.);
Waser, P. M. 1985. Does competition drive dispersal? Ecology 66:1170-1175.