Eckhardt Nadin, Polansky Leo, Boesch Christophe
Max Planck Institute of Evolutionary Anthropology, Department of Primatology, Leipzig, Germany.
Am J Primatol. 2015 Feb;77(2):125-34. doi: 10.1002/ajp.22316. Epub 2014 Sep 24.
Group living animals can exhibit fission-fusion behavior whereby individuals temporarily separate to reduce the costs of living in large groups. Primates living in groups with fission-fusion dynamics face numerous challenges in maintaining spatial cohesion, especially in environments with limited visibility. Here we investigated the spatial cohesion of adult male chimpanzees (Pan troglodytes verus) living in Taï National Park, Côte d'Ivoire, to better understand the mechanisms by which individuals maintain group cohesion during fission-fusion events. Over a 3-year period, we simultaneously tracked the movements of 2-4 males for 4-12 hr on up to 12 consecutive days using handheld GPS devices that recorded locations at one-minute intervals. Analyses of the male's inter-individual distance (IID) showed that the maximum, median, and mean IID values across all observations were 7.2 km, 73 m, and 483 m, respectively. These males (a) had maximum daily IID values below the limits of auditory communication (<1 km) for 63% of the observation time, (b) remained out of visual range (≥100 m) for 46% of observation time, and (c) remained within auditory range for 70% of the time when they were in different parties. We compared the observed distribution of IIDs with a random distribution obtained from permutations of the individuals' travel paths using Kolmogorov-Smirnov tests. Observation IID values were significantly smaller than those generated by the permutation procedure. We conclude that these male chimpanzees actively maintain cohesion when out of sight, and that auditory communication is one likely mechanism by which they do so. We discuss mechanisms by which chimpanzees may maintain the level of cohesion observed. This study provides a first analysis of spatial group cohesion over large distances in forest chimpanzees using high-resolution tracking, and illustrates the utility of such data for quantifying socio-ecological processes in primate ecology.
群居动物可能表现出裂变融合行为，即个体暂时分开以降低生活在大群体中的成本。生活在具有裂变融合动态群体中的灵长类动物在维持空间凝聚力方面面临诸多挑战，尤其是在能见度有限的环境中。在此，我们研究了生活在科特迪瓦塔伊国家公园的成年雄性黑猩猩（黑猩猩指名亚种）的空间凝聚力，以更好地理解个体在裂变融合事件中维持群体凝聚力的机制。在3年时间里，我们使用手持GPS设备，以1分钟的间隔记录位置，连续12天同时跟踪2 - 4只雄性黑猩猩4 - 12小时的活动。对雄性黑猩猩个体间距离（IID）的分析表明，所有观测数据中的最大、中位数和平均IID值分别为7.2千米、73米和483米。这些雄性黑猩猩：（a）在63%的观测时间内，每日最大IID值低于听觉交流的极限（<1千米）；（b）在46%的观测时间内处于视觉范围之外（≥100米）；（c）当它们处于不同群体时，70%的时间内仍处于听觉范围内。我们使用柯尔莫哥洛夫-斯米尔诺夫检验，将观测到的IID分布与通过个体行进路径排列得到的随机分布进行比较。观测到的IID值显著小于排列程序生成的值。我们得出结论，这些雄性黑猩猩在视线之外时会积极维持凝聚力，听觉交流是它们这样做的一种可能机制。我们讨论了黑猩猩可能维持所观测到的凝聚力水平的机制。本研究首次使用高分辨率跟踪技术，对森林黑猩猩在大范围内的空间群体凝聚力进行了分析，并说明了此类数据在量化灵长类生态学中的社会生态过程方面的效用。
