Male social rank and food competition in a primate multi‐level society

Abstract

Objectives: Social animals often have dominance hierarchies, with high rank conferring preferential access to resources. In primates, competition among males is often assumed to occur predominantly over reproductive opportunities. However, competition for food may occur during food shortages, such as in temperate species during winter. Higher-ranked males may thus gain preferential access to high-profitability food, which would enable them to spend longer engaged in activities other than feeding. Materials and methods: We performed a field experiment with a breeding band of golden snub-nosed monkeys, a species that lives in a multi-level society in highaltitude forests in central China. We provisioned monkey's high-profitability food during winter when natural foods are limited, and then recorded the times individual adult males spent engaged in different behaviors. Results: Higher-ranking males spent less time feeding overall and fed on provisioned foods at a higher rate than lower-ranking males. Higher-ranking males therefore had more time to spend on alternative behaviors. We found no significant difference according to rank in times spent moving or resting. However, high-ranking males spend significantly longer on affiliative behaviors with other members of their social sub-units, especially grooming and being groomed, behaviors known to promote social cohesion in primates. Discussion: We show that preferential access to high-profitability foods likely relaxes time-budget constraints to higher-ranking males. High-ranking males thus spend more time on non-feeding activities, especially grooming, which may enhance social cohesion within their social sub-unit. We discuss the potential direct and indirect benefits to high-ranking males associated with preferential access to high-value food during winter.

Behavioural and physiological plasticity in social hierarchies

“…To meet these energetic needs, dominant animals can exhibit several behavioural and physiological changes that adjust energy intake and expenditure. In many species, dominant animals have priority access to food resources, enabling them to increase energy intake, eat higher quality foods and expend less energy in acquiring food [72,73]. Increasing basal or standard metabolic rates is another change that supports the elevated maintenance costs associated with energetically demanding behaviours.…”

Do golden snub-nosed monkeys use deceptive alarm calls during competition for food?

“… 28 The dominance rank in most other primate species is individual based, while that in GSMs is OMU based. 33 The rank of an OMU is the likely result of the combined effects of all adult OMU members, 31 , 34 while the dominance rank among females within the same OMU is unclear or inconsistent. 35 We found that OMU rank did not significantly affect response and escape rates ( Table 2 ).…”

“… 28 , 42 A cohesive breeding band consists of several OMUs, each of which is made-up of a single adult male, several adult females, and their juvenile and infant offspring that tend to forage and socialize together. 33 The breeding band is shadowed by an all-male band (AMB), which consists of bachelor adult males and sub-adult males excluded from the breeding band. 28 , 43 There is a linear dominance hierarchy among OMUs, 31 reflecting sometimes high competition for food within their groups.…”

“… 28 , 43 There is a linear dominance hierarchy among OMUs, 31 reflecting sometimes high competition for food within their groups. 33 , 44 , 45 , 46 The OMUs of a breeding band maintain a close association and coordinate their activities. While each OMU is spatially and socially distinct, the individuals of the same OMU usually stay much closer to each other than to those of other OMUs, and most social interactions occur among the individuals within the same OMU.…”

Not just females: the socio-ecology of social interactions between spider monkey males

“…There is evidence that males and females use resources with the same energy quality to cover their needs [23] and that males travel further to find food [24], suggesting more energy cost than females. Yet, there are practically no studies focusing on food competition between males (see [25] for an exception), and when males are considered, such analyses do not distinguish between sexes (e.g. [26,27]).…”