Weak spatiotemporal response of prey to predation risk in a freely interacting system

1.The extent to which prey space use actively minimises predation risk continues to ignite controversy. Methodological reasons that have hindered consensus include inconsistent measurements of predation risk, biased spatiotemporal scales at which responses are measured, and lack of robust null expectations.

2.We addressed all three challenges in a comprehensive analysis of the spatiotemporal responses of adult female elk (Cervus elaphus) to the risk of predation by grey wolves (Canis lupus) during winter in northern Yellowstone, USA.

3.We quantified spatial overlap between the winter home ranges of GPS‐collared elk and three measures of predation risk: the intensity of wolf space use, the distribution of wolf‐killed elk and vegetation openness. We also assessed whether elk varied their use of areas characterised by more or less predation risk across hours of the day, and estimated encounter rates between simultaneous elk and wolf pack trajectories. We determined whether observed values were significantly lower than expected if elk movements were random with reference to predation risk using a null model approach.

4.Although a small proportion of elk did show a tendency to minimise use of open vegetation at specific times of the day, overall we highlight a notable absence of spatiotemporal response by female elk to the risk of predation posed by wolves in northern Yellowstone.

5.Our results suggest that predator‐prey interactions may not always result in strong spatiotemporal patterns of avoidance.

1. 猎物空间利用主动降低捕食风险的程度这一问题，始终引发学界广泛争议。阻碍研究达成共识的方法论原因包括：捕食风险衡量标准不统一、响应评估的时空尺度存在偏差，以及缺乏稳健的零期望分析基准。
2. 针对美国北黄石地区冬季成年雌性马鹿（Cervus elaphus）对灰狼（Canis lupus）捕食风险的时空响应，我们展开综合分析以解决上述三项方法论难题。
3. 我们量化了佩戴GPS项圈的马鹿冬季家域与三类捕食风险衡量指标间的空间重叠度：灰狼空间利用强度、灰狼猎获马鹿的分布情况，以及植被开阔度。此外，我们还评估了马鹿是否会随每日时段变化，调整其对不同捕食风险水平区域的利用强度，并估算了马鹿与灰狼种群轨迹同时出现的遭遇率。我们采用零模型方法，检验观测值是否显著低于「马鹿运动完全随机且不受捕食风险影响」情境下的预期值。
4. 尽管小部分马鹿确实表现出在每日特定时段减少利用开阔植被的倾向，但整体而言，北黄石地区的雌性马鹿并未展现出针对灰狼捕食风险的显著时空避让响应。
5. 本研究结果表明，捕食者与猎物间的相互作用并非总会催生强烈的时空避让模式。