In most species, daughters remain with their mothers for life, so that the basic social group among Old World monkeys is a matrilineal troop (led by the dominant female). Males leave the group on reaching adolescence, and find a new troop to join. In many species, only a single adult male lives with each group, driving off all rivals, but others are more tolerant, establishing relationships between dominant and subordinate males. Group sizes are highly variable, even within species, depending on the availability of food and other resources.