Changes in African large carnivore diets over the past half-century reveal the loss of large prey

1. Globally, large carnivores are declining due to direct persecution, habitat loss and prey depletion. The effects of prey depletion could be amplified by changes in the composition of the herbivore (prey) community that provoke changes in carnivore diets, but this possibility has received little attention. 2. Here, we tested for changes over the past half century in prey selection by the large carnivore guild in Zambia’s Kafue National Park. 3. Across 52 predator-prey dyads, 71% of the changes we observed were consistent with the hypothesis that large prey have become less important and small prey have become more important. Dietary niche breadth has decreased for KNP carnivores, and niche overlap has consequently increased. 4. We tested whether changes in the importance of prey species are related to their current abundance, and uniformly found that prey that have increased in importance are now relatively common, while those that have decreased in importance are now relatively rare. 5. We identify four potential effects of these changes for conservation (through potential effects on intra-guild competition, group size, the energetics of hunting and vulnerability to snaring) that warrant investigation. Synthesis and applications: Patterns of prey selection by the large carnivores in Kafue National Park have changed appreciably over the past half century. Decreased predation on large prey, which are now relatively rare, has caused niche compression and increased the overlap in carnivore diets. Predation by all of the large carnivores in the ecosystem now concentrates on four small prey species that remain relatively abundant (impala, puku, lechwe and warthog). Methods to detect the changes in predator-prey relationships we observed are well-established, but are rarely applied to large carnivore-ungulate systems. To guide conservation of ecosystem function, monitoring programs should be designed to consider whether prey depletion alters patterns of predation or competition within the predator guild, because these interactions have well-established effects on the distribution and abundance of both predators and prey. If the patterns seen in Kafue prove to be general, then where carnivores are limited by prey depletion, conservation efforts will be most effective if they focus particularly on mitigating the loss of large prey. In Kafue, targeted efforts to protect prey larger than 200 kilograms, particularly buffalo, should be a priority.13-Jun-2018

1. 全球范围内，大型食肉动物因直接迫害、栖息地丧失与猎物枯竭而种群数量持续下降。猎物枯竭的影响可能会因草食动物（猎物）群落组成的改变而加剧——这种改变会引发食肉动物食谱的变化，但该可能性尚未受到足够关注。
2. 本研究针对赞比亚卡富埃国家公园（Kafue National Park）内的大型食肉动物类群过去半个世纪以来的猎物选择变化展开了检验。
3. 在52个捕食者-猎物二元组合中，我们观测到的71%的变化均符合这一假说：大型猎物的重要性下降，而小型猎物的重要性上升。卡富埃国家公园食肉动物的饮食生态位宽度有所减小，生态位重叠度也因此升高。
4. 我们检验了猎物物种重要性的变化与其当前种群丰度之间的关联，结果一致发现：重要性上升的猎物类群如今相对常见，而重要性下降的猎物类群则相对稀少。
5. 我们提出了这些变化对保护工作的四项潜在影响（通过作用于类群内竞争、种群规模、狩猎能量成本以及受套猎捕的风险），这些影响均有待进一步研究。
综合与应用：
卡富埃国家公园内大型食肉动物的猎物选择模式在过去半个世纪中已发生显著变化。对如今已相对稀少的大型猎物的捕食率下降，导致了生态位压缩，并提升了食肉动物间的食谱重叠度。当前该生态系统中所有大型食肉动物的捕食活动均集中于四种仍相对常见的小型猎物物种：黑斑羚（impala）、蒲克羚（puku）、驴羚（lechwe）与疣猪（warthog）。
我们所采用的用于检测捕食者-猎物关系变化的方法已十分成熟，但却极少被应用于大型食肉动物-有蹄类动物系统中。为指导生态系统功能的保护工作，监测方案的设计应考虑猎物枯竭是否会改变捕食者类群内的捕食或竞争模式——此类相互作用对捕食者与猎物的分布及丰度均有明确影响。若卡富埃国家公园观测到的模式具有普适性，那么在食肉动物受限于猎物枯竭的区域，保护工作若能重点缓解大型猎物的流失，将取得最佳成效。在卡富埃国家公园，针对体重超过200千克的猎物（尤其是非洲水牛（buffalo））开展保护的靶向工作应作为优先事项。13-Jun-2018