Mechanistic models suggest that information acquired by animals (“knowledge”) could shape home range patterns and dynamics, and how neighbours share space. In social species this would suggest that immigrants could bring new knowledge into social groups, potentially affecting the dynamics of home range overlap. We tested this “immigrant knowledge hypothesis” in a wild population of chacma baboons (Papio ursinus). We used data collected between 2005 and 2013 on two neighbouring troops in Namibia, comprising GPS records of daily ranges, male natal origins, daily females’ reproductive status, and a satellite index of vegetation growth. We found that when the ratio of fertile females to adult males in the focal troop increased (i.e. increasing inter-troop mating competition costs for focal troop males), the focal troop tended to overlap less with a neighbouring troop’s home range only when the alpha male had immigrated from that neighbouring troop and so was “knowledgeable” about its home range. When the alpha male was “not knowledgeable” the reverse was observed, with troops showing greater overlap, most likely reflecting an influence of fertile females on ranging patterns. Our findings support the immigrant knowledge hypothesis of group ranging behaviour, and suggest that dispersal and spatial memory may sometimes act to increase rather than decrease spatial segregation between groups. Very few previous studies have reported an effect of mating competition on ranging dynamics in social species, perhaps because previous studies did not consider divergent adaptive interest among group members and how they can be solved through collective-decision processes.