Reactive responses of zebras to lion encounters shape their predator-prey space game at large scale

The predator–prey space game and the costs associated with risk effects are affected by prey 1) proactive adjustments (when prey modify their behaviour in response to an a priori assessment of the risk level) and 2) reactive adjustments (when prey have detected an immediate threat). Proactive adjustments are generally well-studied, whereas the frequency, strength and duration of reactive adjustments remain largely unknown. We studied the space use and habitat selection of GPS-collared zebras Equus quagga from 2 to 48 h after an encounter with lions Panthera leo. Lion–zebra encounters generally occurred close to artificial waterholes (< 1 km). Two hours after an encounter, zebras were more likely to have fled than stay when the encounter occurred in more risky bushy areas. During their flight, zebras selected grasslands more than usual, getting great visibility. Regardless of their initial response, zebras finally fled at the end of the night and reached areas located far from waterholes where encounters with lions are less frequent. The large-scale flights (∼4–5 km) of zebras led to a local zebra depression for lions. Zebras that had fled immediately after the encounter resumed their behaviour of coming close to waterholes on the following day. However, zebras that had initially stayed remained far from waterholes for an extra 24 h, remaining an elusive prey for longer. The delay in the flight decision had different short-term consequences on the lion–zebra game. We reveal that the spatial context of the encounter shapes the immediate response of prey, and that encountering predators induces strong behavioural responses: prey flee towards distant, safer, areas and have a constrained use of key resource areas which are at the heart of the predator–prey game at larger spatio-temporal scales. Nighttime encounters were infrequent (once every 35 days on average), zebra responses were short-lived (< 36 h) but occurred over a large spatial scale (several km).

捕食者-猎物空间博弈（predator–prey space game）及其与风险效应相关的成本，受猎物的两类行为调整影响：1）主动性调整（proactive adjustments），即猎物基于对风险水平的先验评估改变自身行为；2）反应性调整（reactive adjustments），即猎物侦测到即时威胁后的行为调整。当前学界对主动性调整已有较为充分的研究，但反应性调整的发生频率、作用强度及持续时长仍未得到充分探明。本研究针对遭遇狮子（Panthera leo）后2至48小时内的佩戴GPS项圈的平原斑马（Equus quagga）的空间利用与栖息地选择行为展开分析。狮-斑马遭遇事件通常发生在人工水坑附近（距离不足1公里）。遭遇发生后的2小时内，若遭遇地点位于风险更高的灌丛区域，斑马更倾向于逃离而非原地停留。在逃离过程中，斑马会比平时更多地选择草原栖息地，以获得更佳视野。无论初始应对策略如何，斑马最终会在夜间结束前逃离，并抵达远离水坑的区域——此类区域遭遇狮子的频率更低。斑马的长距离移动（约4-5公里）会导致狮子所在区域的斑马局部种群密度下降。遭遇后立即逃离的斑马会在次日恢复靠近水坑的行为模式。但初始选择原地停留的斑马则会额外远离水坑24小时，更长时间保持难以被捕食者捕获的状态。逃离决策的延迟会对狮-斑马博弈产生不同的短期影响。本研究表明，遭遇事件的空间场景会塑造猎物的即时应对反应，而遭遇捕食者会引发强烈的行为响应：猎物会逃往更远、更安全的区域，并且在更大的时空尺度下，其对作为捕食者-猎物博弈核心的关键资源区域的利用会受到限制。夜间遭遇事件较为罕见（平均每35天发生一次），斑马的应对反应持续时间较短（不足36小时），但涉及的空间范围较大（可达数公里）。