Climate regulates the suppression of insect herbivory by livestock grazing at a continental scale

Grasslands represent one of the most extensive ecosystems on Earth, yet they are undergoing profound ecological change driven by livestock grazing. Herbivorous insects play a fundamental role in terrestrial food webs and are essential for regulating grassland ecosystem functioning. Yet, the ecological impacts of grazing on insect herbivory and how these are shaped by climate remain illusive. We demonstrate that grazing consistently reduces community-wide insect herbivory, using a continental-scale study across 14 paired sites in China’s major steppes. This pattern likely arises from grazing-induced shifts in plant community composition towards more defended plant taxa. Importantly, we find that climate modulates the effects of grazing on insect herbivory: grazing strongly suppressed herbivory in arid and hot steppes but had minimal impact in regions of lower temperature and aridity. Our study reveals a key contingency in grazing effects, showing that climate fundamentally regulates top-down control of herbivory. This knowledge should be integrated into future grassland conservation frameworks.草原（grasslands）是地球上分布最广泛的生态系统之一，当前却正经历由家畜放牧引发的深刻生态变迁。植食性昆虫（herbivorous insects）在陆地食物网中扮演核心角色，对调控草原生态系统功能至关重要。然而，放牧对昆虫植食作用的生态影响，以及气候如何调控这一过程，至今仍未明晰。本研究通过覆盖中国主要温带草原的14对配对样地开展的大陆尺度调查，证实放牧会持续降低群落水平的昆虫植食作用。该现象大概率源于放牧驱动的植物群落组成向防御型植物类群（defended plant taxa）转变。值得关注的是，本研究发现气候会调控放牧对昆虫植食作用的效应：在干旱炎热的温带草原，放牧会显著抑制昆虫植食作用，但在温湿度较低的区域，放牧的影响则微乎其微。本研究揭示了放牧效应的关键情境依赖性，证实气候从根本上调控着植食作用的下行控制（top-down control）。该研究结论应被纳入未来草原保护框架体系。