Data from: Spatial patterning of prey at reproduction to reduce predation risk: what drives dispersion from groups?

Group-living is a widespread behaviour thought to be an evolutionary adaptation for reducing predation risk. Many group-living species, however, spend a portion of their life cycle as dispersed individuals, suggesting that the costs and benefits of these opposing behaviours vary temporally. Here, we evaluated mechanistic hypotheses for explaining individual dispersion as a tactic for reducing predation risk at reproduction (i.e. birthing) in an otherwise group-living animal. Using simulation analyses parameterized by empirical data, we assessed whether dispersion increases reproductive success by: (i) increasing predator search time, (ii) reducing predator encounter rates because individuals are inconspicuous relative to groups, or (iii) eliminating the risk of multiple kills per encounter. Simulations indicate that dispersion only becomes favourable when detectability increases with group size and there is risk of multiple kills per encounter. This latter effect, however, is likely the primary mechanism driving females to disperse at reproduction because group detectability effects are presumably constant year round. We suggest that the risk of multiple kills imposed by highly vulnerable offspring may be an important factor influencing dispersive behaviour in many species and conservation strategies for such species will require protecting sufficient space to allow dispersion to effectively reduce predation risk.群居行为是一种广泛分布的行为模式，被视为降低捕食风险的进化适应性策略。然而许多群居物种会在生命周期的特定阶段以分散个体的状态存在，这表明这两种对立行为的成本与收益随时间动态变化。本研究针对一种典型群居动物，检验了将个体分散作为繁殖（即分娩）阶段降低捕食风险策略的机制性假说。本研究采用经经验数据参数化的模拟分析，评估了分散行为是否可通过以下三种途径提升繁殖成功率：(i) 延长捕食者的搜索时长；(ii) 降低个体遭遇捕食者的概率——因为相较于群居群体，单个个体更不易被发现；(iii) 消除单次遭遇中多次被捕杀的风险。模拟结果显示，仅当群体的可检测性随种群规模扩大而提升，且单次遭遇存在多次被捕杀的风险时，分散行为才具备演化优势。不过，由于群体可检测性的影响全年大致恒定，单次遭遇多杀风险这一效应，或许是驱使雌性个体在繁殖阶段选择分散行为的核心机制。我们认为，极易受到攻击的幼崽所带来的单次多杀风险，可能是影响诸多物种分散行为的重要因素；针对这些物种的保护策略，需保障足够的生存空间，以使分散行为能够有效降低捕食风险。