Predation risk constrains herbivores’ adaptive capacity to warming

Global warming compels larger endothermic animals to adapt either physiologically or behaviourally to avoid thermal stress, especially in tropical ecosystems. Their adaptive responses may however be compromised by other constraints, such as predation risk or starvation. Using an exceptional camera trap dataset spanning 32 protected areas across Southern Africa, we find that intermediate-sized herbivores (100-550kg) switch activity to hotter times of the day when exposed to predation by lions. These herbivores thus face a tight window for foraging activity being exposed to nocturnal predation and to heat during the day, suggesting a trade-off between predation risk and thermoregulation mediated by body size. These findings stress the importance of incorporating trophic interactions into climate change predictions.全球变暖迫使体型更大的恒温动物（endothermic animals）通过生理或行为层面的适应策略规避热应激，这一情况在热带生态系统中尤为突出。然而，这类动物的适应性响应可能会受到其他制约因素的干扰，例如捕食风险或饥饿胁迫。本研究依托覆盖非洲南部32个保护区的高质量红外相机陷阱（camera trap）数据集，研究发现：体重介于100千克至550千克的中型植食动物在面临狮子的捕食威胁时，会将自身活动时段调整至当日温度更高的时间段。此类植食动物因此面临极为狭窄的觅食窗口：它们需在夜间承受捕食威胁，日间则暴露于热应激之下，这表明体型介导了捕食风险与体温调节之间的权衡关系。本研究结果凸显了将营养级交互作用纳入气候变化预测模型的重要性。