Data from: Cape buffalo (Syncerus caffer caffer) social dynamics in a flood-pulsed environment

Fission-fusion social dynamics allow animals to respond to short-term environmental changes by temporarily adjusting group size. The drivers of such complex social dynamics are thought to relate to resource availability, density effects and social interactions. During 2008-09, we collared 15 Cape buffalo (Syncerus caffer caffer) cows in different groups in the Okavango Delta, Botswana, to study social dynamics in a flood-pulsed ecosystem. Hierarchical clustering identified 2 subpopulations, 1 migratory and 1 resident. We calculated Utilization Distribution Overlap Index (UDOI) and number and duration of fusion events between buffalo dyads and related them to environmental variables. Number of fusion events and duration of fusion periods did not vary seasonally, total fusion time varied seasonally and annually, and UDOI varied with year and subpopulation. Fission events were more likely in cluttered habitats, but only in the late flood season. There was more open habitat in home range overlap (HRO) areas than home ranges (HR) in most seasons. Pan density in rainy season HROs was lower and higher than in HRs in 2008 and 2009, respectively, and in all flood seasons HRO areas were closer to permanent water than HRs, suggesting that fusion occurred when buffalo congregated on resources. Whereas previous studies described large herds that sometimes split, we identified numerous smaller groups that occasionally fused, indicating a very fluid social system. Our results highlight the need to understand social system flexibility to ensure appropriate management and understand the varying impacts of environmental and anthropogenic effects on subpopulations within the same geographic area.裂变-融合社会动态（Fission-fusion social dynamics）可使动物通过临时调整群体规模，响应短期环境变化。这类复杂社会动态的驱动机制，被认为与资源可获得性、密度效应及社会互动密切相关。2008—2009年，研究团队在博茨瓦纳奥卡万戈三角洲的不同水牛群体中，为15头母南非水牛（Syncerus caffer caffer）佩戴项圈，以探究该洪水脉冲生态系统中的社会动态。通过系统聚类（hierarchical clustering）分析，研究识别出两个亚种群：一个为迁徙型亚种群，另一个为定居型亚种群。研究团队计算了利用分布重叠指数（Utilization Distribution Overlap Index, UDOI）、水牛配对间融合事件的数量与持续时长，并将这些指标与环境变量进行关联分析。结果显示，融合事件数量与融合周期时长无显著季节变化，总融合时长则存在季节与年度差异，而UDOI则随年份与亚种群的不同而变化。分裂事件更易发生在生境结构复杂的区域，但该规律仅在洪水季后期成立。多数季节中，家域重叠（home range overlap, HRO）区域的开阔生境占比高于单纯家域（home range, HR）。雨季HRO区域的水塘密度在2008年低于家域，2009年则高于家域；且在所有洪水季，HRO区域均比家域更靠近永久性水源，这表明水牛的融合行为发生在它们聚集于资源点之时。既往相关研究多聚焦于偶尔会发生分裂的大型兽群，而本研究则识别出众多偶尔会发生融合的小型群体，这表明该水牛种群拥有极为灵活的社会系统。本研究结果凸显了理解社会系统灵活性的重要性，这可为制定恰当的野生动物管理策略提供支撑，同时有助于厘清环境与人为扰动对同一地理区域内不同亚种群的差异化影响。