Omus

Abstract: We describe the social organization, mating system, and social structure of a group of hybrid baboons (Papio anubis×P. hamadryas) in Ethiopia's Awash National Park. The group contained elements of both hamadryas and anubis societies. Overall, the group was a multimale, multifemale group that lacked cohesion and frequently formed subgroups. Subgroup formation was more strongly associated with predation risk than food availability. Although there were several hamadryas-like one-male units OMUs within the group, there was no evidence of a hamadryas multilevel society. Male and female members of OMUs were phenotypically more hamadryas-like than non-OMU individuals. The group contained substantial variation in the strength of inter- and intrasexual bonds: some females primarily groomed males while other females primarily groomed females, and the patterns were consistent with the OMU substructure. Despite some promiscuous mating, mating was biased towards the hamadryas condition for all group members. Additionally, rates of immigration and emigration were very low, and mean pairwise relatedness within the group is rising. For measures of intersexual bonding, all members of the group were intermediate between anubis and hamadryas individuals in less hybridized groups. The group was phenotypically and behaviorally more intermediate than it was in the 1970s (Sugawara, K. (1988). Primates 29: 429–448.) and the changes may indicate a relatively young and dynamic hybrid zone.

Abstract: A one-male unit (OMU) of chacma baboons (Papio ursinus) in northern Botswana formed by the asymmetrical fissioning of a multimale (MM) group. During long-term (13 years) observations in this area, which has a relatively high density of baboons, we observed only MM groups with 6 or more adult males per group (N = 19). The behavioral repertoire of the OMU generated a pattern of sociality unrepresentative of these MM groups. Distinctive behavior patterns expressed by the male of the OMU included vigilance oriented away from the group and suppression of intra-group aggression among all other group members. There was also a difference between the foraging and movement patterns of the OMU and those of MM groups in environmentally similar or the same areas. The OMU moved and foraged in a cohesive formation and all group members often foraged in single fruiting trees. Under comparable circumstances at the same time and places MM groups foraged in dispersed formation. Diet and habitat choices of the OMU differed from those of neighboring groups. Patterns of sociality associated with OMUs have been interpreted as responses to extreme environmental conditions [Byrne et al.: Am J Primatol 20:313–329, 1990]. However, it is also possible that alternative behavior patterns are facultative tactical responses to social circumstances, The alternative social styles of OMUs arising within typically MM populations identify the breadth of the behavioral repertoire and the capacity for social flexibility within contemporary savanna baboon and perhaps other primate populations. © 1992 Wiley-Liss, Inc.

Abstract: The nested one-male units (OMUs) of the hamadryas baboon are part of a complex social system in which "leader" males achieve near exclusive mating access by forcibly herding females into permanent consortships. Within this multi-level social system (troops, bands, clans and OMUs) are two types of prereproductive males--the follower and solitary male--whose different trajectories converge on the leader role. Here we compare OMU formation strategies of followers, who associate with a particular OMU and may have social access to females, with those of solitary males, who move freely within the band and do not associate regularly with OMUs. Data were derived from 42 OMU formations (16 by followers and 26 by solitary males) occurring over 8 years in a hamadryas baboon band at the Filoha site in Ethiopia. "Initial units" (IUs) with sexually immature females (IU strategy) were formed by 44% of followers and 46% of solitary males. The remaining followers took over mature females when their leader was deposed (challenge strategy) or disappeared (opportunistic strategy), or via a seemingly peaceful transfer (inheritance strategy). Solitary males took over mature females from other clans and bands, but mainly from old, injured or vanished leaders within their clan (via both the challenge and opportunistic strategies). Former followers of an OMU were more successful at taking over females from those OMUs than any other category of male. Despite this advantage enjoyed by ex-follower leaders, ex-solitary leaders were equally capable of increasing their OMU size at a comparable rate in their first 2 years as a leader. These results demonstrate the potential for males to employ both multiple roles (follower vs. solitary male) and multiple routes (IU, inheritance, challenge, opportunistic) to acquire females and become a leader male in a mating system characterized by female defense polygyny in a competitive arena.

Abstract: We studied the dominance relationships among one-male units (OMUs) in a provisioned free-ranging band of the Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains of central China from 2001 to 2005 The band was composed of 6-8 OMUs that stayed in the band for several years Linear dominance orders could be detected using displacement interactions with directional asymmetry among OMUs in 823+/-5% of interactions, and ambiguous and reversed interactions in 177+/-5% The dominance rank of OMUs was positively related with the duration of their stay in the band, and this may be attributed to the association of the resident male with adult females, rather than the fighting ability of resident males, as males do not fight seriously with each other Subordinate units were observed to merge with dominant units resulting in an elevation of their rank order The linear dominance relationship among OMUs in the Sichuan snub-nosed monkeys may have evolved as a result of competition for preferred food trees