Contrasting mechanisms underlying macroinvertebrate community assembly between river and lake ecosystems in the Qinghai-Tibet Plateau

Elucidating the mechanisms that govern community assembly remains a core pursuit in community ecology. However, few studies have simultaneously compared different aquatic ecosystems while also accounting for their temporal dynamics. Here, we investigated the spatio-temporal patterns and underlying drivers of macroinvertebrate diversity in Qinghai Lake and its inflowing rivers on the Qinghai-Tibet Plateau. Our results revealed stronger spatial than temporal variation in community structure and diversity. River sites exhibited higher alpha diversity, particularly during the wet season, whereas lake sites exhibited greater beta diversity, driven largely by species turnover. Results from the Elements of Metacommunity Structure, variation partitioning and null model analyses collectively revealed distinct spatio-temporal metacommunity dynamics. River communities consistently exhibited a quasi-clumped species loss structure, indicative of patchy extinctions potentially driven by heterogeneous disturbance regimes. In contrast, lake communities exhibited a seasonal shift from a Gleasonian structure in the dry season—characterized by individualistic species responses—to quasi-Clementsian gradients in the wet season, reflecting more coordinated responses to environmental variation. Deterministic processes generally predominated overall, particularly at lake sites, although the relative strength of both processes varied seasonally and across ecosystems. At lake sites, strong abiotic gradients transcended seasonal fluctuations and imposed powerful niche-based controls on community assembly. At river sites, however, stochasticity became comparatively more important during the wet season, driven by intensified hydrological disturbance that compromised environmental filtering. Overall, this study highlights the ecosystem-specific nature of community assembly processes and underscores the importance of considering both spatial and temporal scales for effective aquatic bioassessment and ecosystem management. • We investigated the spatio-temporal patterns of macroinvertebrate diversity and their drivers in the Qinghai-Tibet Plateau. • River sites showed higher alpha diversity, while lake sites maintained greater beta diversity. • Deterministic processes dominated in lake sites, whereas stochasticity played a more dominant role in river sites. • Seasonal changes significantly influenced metacommunity structure, biodiversity patterns and community assembly mechanisms. • Our findings provide important implications for biodiversity conservation and bioassessment in highland aquatic ecosystems.