Herbivore species asynchrony underpins multitrophic stability across plants, herbivores and predators.

Ecological stability is fundamental to sustaining ecosystem functioning amid accelerating global environmental change. Both theoretical and empirical evidence suggest that biological diversity and composition influence species asynchrony and species stability within individual trophic levels, thereby contributing to greater temporal stability at the community level. Nonetheless, it remains unclear whether and how these stabilizing factors are integrated across trophic levels to determine multitrophic stability. In this study, using 3 years of community data collected approximately 10 years after the manipulation of plant diversity in a grassland biodiversity experiment, we used structural equation models to assess how species richness, functional composition, species asynchrony and species stability within plant, herbivore and predator communities were associated with multitrophic stability. We quantified multitrophic stability in two complementary ways: an averaging approach, based on the overall mean stability across trophic levels, and a multiple-threshold approach, based on how many trophic levels maintained high stability concurrently. This framework allowed us to examine whether key predictors of multitrophic stability were shared between the two metrics or differed depending on the metric used. Asynchrony among species within each trophic group typically contributed to enhanced community stability. At the multitrophic level, analyses using the averaging approach revealed that average multitrophic stability was positively associated with herbivore species asynchrony and richness, predator functional composition and predator species asynchrony, with herbivore species asynchrony showing a particularly strong positive relationship. Similarly, employing the multiple threshold approach, which evaluated how many trophic levels exceeded 50%, 60%, 70% or 80% of the maximum stability, further identified herbivore species asynchrony as a significant positive predictor at 70% and 80% stability thresholds. Herbivore species richness, by contrast, showed threshold-dependent effects, with positive indirect effects at the 70% and 80% thresholds but negative direct effects at the 50% and 70% thresholds, potentially attributable to diminished plant community stability. Our findings suggest that multitrophic stability across plants, herbivores and predators is most closely associated with the compensatory dynamics of the intermediate consumer trophic level-specifically, herbivores-highlighting this trophic level as a key contributor to buffering temporal fluctuations in multitrophic communities.