Abstract The biodiversity hotspot region of the Eastern Himalayas consists of a vast freshwater network enriched with species diversity. Many small-scale torrential rivers and water reaches contribute to the species pool of all the major rivers by converging downstream. These reaches are most likely to be degraded at a faster rate as compared to the large-scale rivers following an increased rate of urbanization, habitat alterations, and changing climatic conditions. Therefore, this study aims to explore River Murti, which is a representative small scale river system characterized by a large altitudinal gradient and a diverse watershed area. Ichthyofaunal diversity (i.e., diversity, evenness & richness) and 21 environmental variables are measured through a tri-seasonal sampling effort conducted along 14 selected locations. A total of 41 fish species (including species belonging to 4 Near Threatened, 8 Vulnerable, and 1 Endangered) are found inhabiting this river. Ichthyofaunal assemblage is found to be primarily modulated by habitat diversity and landscape variables. Three Aquatic Ecological Systems (AES) have been identified along this river in a top-down approach based on recorded environmental variables. We have calculated an observed/expected ratio for each diversity indices along 14 locations based on predicted temporal variability using boosted regression (BRT) models. The evaluation of diversity status has been kept at 0.5 to account for a 50% loss or deviation from observed (O/E50). This evaluation has been successfully used to delineate AES1 with majorly “Impaired” status and thus ensures its importance in terms of species conservation. Our study indicates the contribution of 11 major environmental drivers modulating the species assemblage patterns in these AES. Amongst them, altitude, substrate coarseness, river morphology, and shelter availability are strongly associated with species diversity as per the BRT models. These underlying factors are also correlated with “basin pressure,” suggesting that anthropogenic disturbances, as well as the changing climate, might play an important role in the gradual change in environmental conditions, which in turn could cause a shift in species assemblage structure.

中文翻译：

---

通过喜马拉雅河流中鱼群多样性动态评估水生生态系统，穆尔蒂

摘要 东喜马拉雅山的生物多样性热点地区由一个丰富的物种多样性的广阔淡水网络组成。许多小规模的洪流河流和水位通过向下游汇流而形成所有主要河流的物种库。随着城市化速度的加快、栖息地的改变和气候条件的变化，与大型河流相比，这些河段最有可能以更快的速度退化。因此，本研究旨在探索穆尔蒂河（River Murti），这是一个具有代表性的小规模河流系统，其特点是海拔梯度大，流域面积多样。鱼类动物多样性（即多样性、均匀度和丰富度）和 21 个环境变量是通过在 14 个选定地点进行的三季节采样工作来测量的。在这条河流中发现了总共 41 种鱼类（包括属于 4 种近危、8 种易危和 1 种濒危）。发现鱼类群落主要受栖息地多样性和景观变量的调节。根据记录的环境变量，以自上而下的方法沿这条河确定了三个水生生态系统 (AES)。我们使用增强回归 (BRT) 模型基于预测的时间变异性计算了 14 个位置的每个多样性指数的观察/预期比率。多样性状态的评估一直保持在 0.5，以解释 50% 的损失或与观察结果的偏差 (O/E50)。该评估已成功用于描述处于主要“受损”状态的 AES1，从而确保其在物种保护方面的重要性。我们的研究表明 11 个主要环境驱动因素对这些 AES 中物种组合模式的影响。其中，根据 BRT 模型，海拔、底物粗度、河流形态和庇护所的可用性与物种多样性密切相关。这些潜在因素也与“盆地压力”相关，表明人为干扰以及气候变化可能在环境条件的逐渐变化中发挥重要作用，进而可能导致物种组合结构的变化。