The relative influence of density and kinship on dispersal in the common lizard

We experimentally investigated the relative role of kinship and density on juvenile dispersal in the common lizard. A few days after birth, juveniles were introduced into seminatural enclosures, where they experienced differe nt social environments: in the first experiment we varied the density of un related adults (males or females) within the enclosure (0, 1, or 2 adults), and in the second experiment, we varied the level of kinship and familiari ty between juveniles and adults. Each enclosure was connected to a second e nclosure by small holes which allowed only juveniles to move between enclos ures. Juvenile movements were monitored during 14 days after birth, as juve nile dispersal is mainly completed within 10 days after birth under natural conditions. Most juveniles did not return to the first enclosure. Sex had no effect on juvenile dispersal. Adult density and kinship with adults both affected dispersal. Adult female density increased juvenile dispersal what ever the level of kinship and familiarity with the females. Dispersers had better body condition than nondispersers at high female density, and this d ifference was significantly greater when the mother and the familiar female were present in the enclosure. Furthermore, body condition of mothers and familiar females was positively correlated with juvenile dispersal, whereas there was no such correlation in the case of unfamiliar and unrelated fema les. These results strongly suggest that adult female density is a major fa ctor promoting dispersal in this species and that both intraspecific and ki n competition motivate dispersal.