Summary: Pappano et al. (2012)

 Living in a group confers numerous benefits, such as reduced energy expenditure for thermoregulation (social huddling), increased predator detection (with reduced individual vigilance - the "many eyes" hypothesis) and increased predator defence (e.g. mobbing by many). Hamilton (1971) postulated that groups form because individuals are inherently selfish and grouping can diminish costs associated with living alone. Both De Vos & O'Riain (2010) and Quinn & Cresswell (2006) have demonstrated that the the central tenets of the "selfish herd hypothesis" can hold true in some mammals and birds. Pappano et al. (2012) postulate that this idea can also translate to "social predators" - infanticidal males. They proposed that the impact of a non-breeding, potentially infanticidal bachelor male geladas Theropithecus gelada, could alter spacing patterns of  reproductive units within a group. Their findings suggest that these social predators are capable of causing group spacing dynamics to change: 1) numbers of animals in a group increased with an increasing number of bachelor males; 2) breeding individuals moved into closer contact with neighbours closest to them; and 3) reproductive females associated more with reproductive males. Pappano et al.'s (2012) study indicates that spacing patterns of individuals could offset the costs of potentially associating with social predators within groups.