Initial age structure influences the growth of a prey population and the ou
tcome of the predator-prey interaction. In order to quantify that influence
, we employed a simple numerical model using experimental data from the sys
tem Tetranychus urticae-Phytoseiulus persimilis. Four major points were dra
wn from the results: (1) A population created by young females grows much f
aster than a population created by the same number of females but distribut
ed among the stable age structure. Final number of individuals after a few
generations is then much higher than what a plant could support. Consequent
ly, a stable age structure is probably never achieved under these condition
s; (2) In the presence of a predator, such a population can persist for a s
ufficiently long time to overexploit its host plant and to produce enough i
ndividuals to allow dispersal; (3) The impact of the predator on the prey p
opulation is drastically different according to its own age structure at th
e beginning of the interaction; and (4) Predators disturb the prey age stru
cture during the course of interactions and thus maintain the prey growth p
otential at a high level. These points constitute an important adaptation t
hat determine the persistence of the prey and the predator at a metapopulat
ion level. They bring a new insight on the adaptive characters of young fem
ale dispersal. (C) 1999 Published by Elsevier Science B.V. All rights reser
ved.