CAS Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
Am J Primatol. 2018 Jul;80(7):e22881. doi: 10.1002/ajp.22881. Epub 2018 Jun 19.
In the present study, we compared mother-infant relationships in 57 mother-infant dyads residing in two wild, semi-provisioned (22 mother-infant dyads in 2014, 35 dyads in 2015) groups of rhesus macaques (Macaca mulatta) in the Nanwan Nature Reserve for Rhesus Macaques, Hainan, China. We also compared reproductive success between these two groups. The ecology and provisioning regime for each group was similar. These groups differed however, in size. Group 1 contained ∼35 individuals and Group 2 contained ∼120 individuals. Data were collected over a 2-year period (2014-2015). We found that during the birth season, mother-infant relationships in the larger group were characterized by less time in contact and more time separated than in the smaller group. Mothers in the smaller group initiated more contact and proximity with their infants. During the mating season when infants were approximately 6 months old, mother-infant relationships in the smaller group were more rejecting. We also found that birth rates were significantly higher but infant survivorship (to 1-year-old) was significantly lower in the smaller group. Moreover, higher-ranking mothers in the larger group were characterized by a higher reproductive output than females of lower rank. In the smaller group, female rank did not affect reproductive output. There was, however, no clear relationship between infant survivorship and maternal rank. We hypothesize that differences in reproductive success and changes in mother-infant relationships between the birth and mating seasons reflect differences in the costs and benefits of group size: females in the larger group faced (i) higher intragroup feeding competition leading to a reduction in birth rate but also (ii) lower predation risk, resulting in higher infant survival rate compared to females in the smaller group. The results of this study point to the tradeoffs that primate females face in living in smaller and larger social groups.
在本研究中，我们比较了生活在中国海南南湾自然保护区恒河猴（Macaca mulatta）两个半野生、半投喂（2014 年 22 个母婴对，2015 年 35 个母婴对）群体中的母婴关系。我们还比较了这两组的繁殖成功率。两组的生态和投喂制度相似，但群体大小不同。第 1 组包含约 35 只个体，第 2 组包含约 120 只个体。数据收集时间为 2014 年至 2015 年的 2 年。我们发现，在分娩季节，大群体中的母婴关系表现为接触时间较少，分离时间较多，而小群体中的母婴关系则相反。小群体中的母亲会更多地与婴儿接触和接近。在婴儿大约 6 个月大的交配季节，小群体中的母婴关系更具排斥性。我们还发现，小群体的出生率显著较高，但婴儿存活率（到 1 岁）显著较低。此外，大群体中等级较高的母亲的繁殖产出高于等级较低的女性。在小群体中，女性等级不会影响繁殖产出。然而，婴儿存活率与母亲等级之间没有明显的关系。我们假设，繁殖成功率的差异和分娩季节与交配季节之间母婴关系的变化反映了群体大小的成本和收益的差异：大群体中的雌性面临（i）更高的群体内觅食竞争，导致出生率降低，但也（ii）较低的捕食风险，与小群体中的雌性相比，婴儿的存活率更高。本研究的结果表明，灵长类雌性在生活在较小和较大的社会群体中面临着权衡。
