Data from: Group size differences may mask underlying similarities in social structure amongst female elephants

Fission-fusion dynamics allow for the costs and benefits of sociality to be regulated through changes in group size. There are different modal fission-fusion societies, and female Asian and African elephant populations examined so far have shown different social structures and average group sizes. We report on female Asian elephant social structure in Nagarahole and Bandipur National Parks (Kabini population), southern India, and examine the role of group size in affecting the outcome of social structure analysis in female elephants. Based on five years of data, we found the Kabini association network structured into highly modular communities that we call clans. A comparison of the Kabini dataset, modified to match sampling methods, with previously published Uda Walawe Asian elephant and Samburu African elephant data showed that measures of association and network structure were more similar amongst the Asian elephant populations compared to Samburu. The Samburu population formed a hierarchically-nested multilevel society whereas the Asian populations did not. However, we found hierarchical levels in all three populations using Louvain community detection. Moreover, the average community sizes obtained through the Louvain method were not significantly different across populations, indicating basic similarities in social structure. We examined the effect of average group size on association and network statistics. Higher average association index and degree, and lower average path length in Samburu compared to Kabini were explained by larger average group size in Samburu. Thus, underlying similarities in the social networks of species showing fission-fusion dynamics may be obscured by differences in average group size.

裂变-融合动态（fission-fusion dynamics）可通过群体规模的变化调节社会性的成本与收益。目前已开展研究的不同模式的裂变-融合社会中，雌性亚洲象与非洲象种群均展现出各异的社会结构与平均群体规模。本研究针对印度南部纳加尔霍尔国家公园与班迪普尔国家公园内的雌性亚洲象（卡比尼种群）的社会结构展开报道，并探究群体规模对雌性大象社会结构分析结果的影响。基于五年的观测数据，我们发现卡比尼种群的关联网络（association network）可划分为高度模块化的社群，我们将其命名为氏族（clans）。将经过采样方法标准化调整后的卡比尼数据集，与此前公开的乌达瓦拉维亚洲象数据集及桑布卢非洲象数据集进行对比后发现，亚洲象种群间的关联指标与网络结构相似度，高于其与桑布卢非洲象种群的相似度。桑布卢非洲象种群形成了层级嵌套的多层社会结构，而亚洲象种群则未呈现该特征。不过，通过卢万社群检测算法（Louvain community detection），我们在三个种群中均识别出了层级结构。此外，通过卢万算法得到的平均社群规模在各群体间无显著差异，这表明其社会结构存在基本相似性。我们还探究了平均群体规模对关联指标与网络统计特征的影响。相较于卡比尼种群，桑布卢种群拥有更高的平均关联指数与网络度，以及更低的平均路径长度，这一差异可通过桑布卢种群更大的平均群体规模得到合理解释。因此，展现裂变-融合动态的物种间，其社会网络潜在的相似性可能因平均群体规模的差异而被掩盖。