Résumé
Understanding dispersal behaviour and its determinants is critical for
studies on life-history maximizing strategies. Although many studies have
investigated the causes of dispersal, few have focused on the importance
of sibship, despite that sibling interactions are predicted to lead to
intrafamilial differences in dispersal patterns. Using a large demographic
data set from pre-industrial Finland (n = 9000), we tested whether the
sex-specific probability of dispersal depended on the presence of same-sex
or opposite-sex elder siblings who can both compete and cooperate in the
family. Overall, following our predictions, the presence of same-sex elder
siblings increased the probability of dispersal from natal population for
both sexes, whereas the number of opposite-sex siblings had less
influence. Among males, dispersal was strongly linked to access to land
resources. Female dispersal was mainly associated with competition over
availability of mates but likely mediated by competition over access to
wealthy mates rather mate availability per se. Besides ecological
constraints, sibling interactions are strongly linked with dispersal
decisions and need to be better considered in the studies on the evolution
of family dynamics and fitness maximizing strategies in humans and other
species.