Data from: Climate and the landscape of fear in an African savanna

1.Herbivores frequently have to make tradeoffs between two basic needs: the need to acquire forage and the need to avoid predation. One manifestation of this tradeoff is the “landscape of fear” phenomenon – wherein herbivores avoid areas of high perceived predation risk even if forage is abundant or of high quality in those areas. Although this phenomenon is well-established among invertebrates, its applicability to terrestrial large herbivores remains debated, in part because experimental evidence is scarce. 2.This study was designed to (a) experimentally test the effects of tree density – a key landscape feature associated with predation risk for African ungulates – on herbivore habitat use, and (b) establish whether habitat use patterns could be explained by tradeoffs between foraging opportunities and predation risk-avoidance. 3.In a Kenyan savanna system, replicate plots dominated by the tree Acacia drepanolobium were cleared, thinned, or left intact. Ungulate responses were measured over four years, which included years of moderate rainfall as well as a severe drought. 4.Under average rainfall conditions, most herbivores (primarily plains zebra, Grant's gazelle, and hartebeest) favored sites with fewer trees and higher visibility – regardless of grass production – while elephants (too large to be vulnerable to predation) favored sites with many trees. During the drought, however, herbivores favored sites that had high grass biomass, but not high visibility. Thus, during the drought, herbivores sought areas where food was more abundant, despite probable higher risk of predation. 5.These results illustrate that the “landscape of fear”, and the associated interactions between top-down and bottom-up effects, is not static, but rather shifts markedly under different conditions. Climate thus has the potential to alter the strength and spatial dynamics of behaviorally-mediated cascades in large herbivore systems.1. 草食动物往往需要在两项核心生存需求间做出权衡：获取草料的需求与规避捕食的需求。这一权衡的典型表现即为恐惧景观（landscape of fear）现象：即便某区域内草料充足且品质上乘，草食动物仍会主动规避该区域中被其感知为捕食风险较高的地段。尽管这一现象在无脊椎动物中已得到充分证实，但其对陆地大型草食动物的适用性仍存在争议，部分原因在于相关实验证据较为匮乏。 2. 本研究旨在达成两大研究目标：(a) 通过实验检验树木密度——这一与非洲有蹄类动物捕食风险密切相关的关键景观特征——对草食动物生境利用的影响；(b) 验证草食动物的生境利用模式是否可通过觅食机会与捕食风险规避间的权衡关系得到解释。 3. 在肯尼亚稀树草原生态系统中，研究人员对以黑刺金合欢（Acacia drepanolobium）为优势种的重复样地开展了三种处理：全部清除、适度疏伐或保留原状。随后对有蹄类动物的响应进行了为期四年的监测，监测时段涵盖降雨中等的年份与一次严重干旱年份。 4. 在平均降雨条件下，多数草食动物（主要为平原斑马、葛氏瞪羚与转角牛羚）更偏好树木更少、视野更佳的地段，其生境选择不受草料产量的影响；而体型过大而无被捕食风险的大象，则更偏好树木茂密的地段。然而在干旱期间，草食动物转而更偏好草料生物量较高的地段，而非视野更佳的区域。这意味着在干旱时期，尽管捕食风险可能更高，草食动物仍会选择食物更为充足的区域。 5. 上述研究结果表明，恐惧景观及其所关联的自上而下与自下而上生态效应间的相互作用并非静态不变，而是会随环境条件发生显著变化。因此，气候有可能改变大型草食动物系统中行为介导级联效应的强度与空间动态。