From Source to Lake: Multi‒taxon Alpha and Beta Diversity Patterns along a River above 4500 M Amsl on the Qinghai‒Tibet Plateau

Understanding the distribution of species is highly important for optimizing future conservation priorities and strategies at the regional scale. Relatively little attention has been given to multi-taxon aquatic biota in extreme alpine environments. We examined the spatial and temporal patterns of alpha and beta diversity, site-specific contributions to beta diversity and assembly mechanisms of four taxonomic groups (fishes, macroinvertebrates, zooplankton and phytoplankton) from the source to the estuary of the Za’gya Zangbo River above 4500 m AMSL on the northern Qinghai-Tibetan (Q–T) Plateau. A total of 4 fish species, 45 macroinvertebrate taxa, 17 zooplankton taxa and 56 phytoplankton taxa were found in the study area. No consistent patterns in taxonomic richness were observed across taxa from upstream to estuary. The fish communities had the lowest dissimilarity between communities, the phytoplankton community had the highest dissimilarity in the dry season, and the macroinvertebrate community had the highest dissimilarity in the wet season. The relative importance of the turnover and nestedness components varied considerably across taxa and along spatial gradients. The diversity patterns of macroinvertebrate, zooplankton and phytoplankton communities were significantly correlated with several environmental factors, whereas only the beta diversity of fish was correlated with altitude. Stochastic processes dominated in shaping the macroinvertebrate communities whereas deterministic processes dominated the assembly of the phytoplankton communities. Weak congruence of diversity patterns across taxonomic groups suggested that biological groups cannot serve as reliable surrogates for one another and that multiple biological groups should be included in the biomonitoring of high-altitude rivers on the Q‒T Plateau. The relatively unique species in the upstream area and estuary of the Za’gya Zangbo River harbor should receive more attention in future conservation and management schemes.