Drying alters regional metacommunity processes-but not local ones-across drying river networks of the Qinghai-Tibet Plateau area, China.

With climate change, the increasing frequency of extreme hydrological events leads to shifts from perennial rivers and streams (PRs), which flow all year round, to non-perennial rivers and streams (NPRs), which dry up or cease flow on an annual basis. Understanding current biodiversity patterns and the underlying drivers of in NPRs is therefore needed to anticipate the future of riverine biodiversity. However, if NPRs research has gained a lot of attention in the past decade, empirical evidence from high-altitude regions, where NPRs are widespread such as Asia, remains extremely scarce. In such context, the prevailing environmental harshness could mitigate the reported major effects of drying on biological communities from temperate and Mediterranean regions. In this study, we quantified the taxonomic and functional alpha and beta diversity of macroinvertebrates communities across 62 sites spanning PRs and NPRs in the Qinghai Lake Basin, a high-altitude dryland region from the Tibetan Plateau. As expected, our results showed that alpha diversity did not differ between PRs and NPRs, probably due to co-tolerance of organisms to multiple environmental stressors such as flooding, scouring, extreme temperatures and drying. In contrast, beta diversity was higher in NPRs compared to PRs and was best explained by environmental variables (environmental filtering), while spatial variables (e.g., dispersal limitation) dominated in PRs, contrary to what we expected. Altogether, our results suggest that in high-altitude regions prone to environmental harshness and multiple disturbance regimes, river drying does not cause local species loss, but promotes community reorganization by shifting the balance between stochastic (dispersal limitation) and deterministic (environmental filtering) processes. These findings provide the first evidence of the limited effects of drying from the Qinghai–Tibet Plateau building on recent findings demonstrating the context-dependence of drying effects on riverine biodiversity, offering valuable insights for conservation and management efforts in these unique regions.