Opposing diversity-stability relationships within versus between aquatic producers and consumers.

While the role of biodiversity in enhancing temporal stability is well established within single trophic levels, how biodiversity at one trophic level affects stability at adjacent trophic levels remains poorly understood. To address this knowledge gap, we analyzed the relationships between diversity and stability both within and across producer (algae) and consumer (invertebrate) communities using time series from 97 aquatic food webs across the world. Within consumer communities, we found that greater species diversity was associated with increases in both population asynchrony and average population stability, leading to higher community stability. Within producer communities, producer diversity was positively associated with population asynchrony but negatively associated with population stability, resulting in no net effect. In contrast, we found consistently negative diversity-stability relationships across trophic levels: increased producer diversity was linked to decreased consumer community stability and increased consumer diversity was associated with decreased producer community stability. These negative relationships stem from adverse impacts of diversity on population stability across trophic levels, which may be due to the altered producer dynamics and intensified top-down pressure. Our findings demonstrate that incorporating antagonistic interactions between trophic levels in natural communities may alter the positive diversity-stability relationships that are typically observed in single trophic communities.