Long-term changes in the functional trait composition and diversity of fish assemblages in eastern plain lakes under the regime of river-lake connectivity loss

Abstract

东部平原湖泊区是我国淡水湖泊最集中的地区，分布着我国的五大淡水湖等诸多湖泊.然而，江湖阻隔对该区域湖泊的生物多样性造成严重威胁.本文选取东部平原的9个湖泊，对江湖阻隔前后鱼类功能性状（3组分类性状和6个连续性状）和功能多样性指数的变化规律开展了研究.结果表明，9个湖泊的鱼类总物种数由江湖阻隔前的140种减少为江湖阻隔后的100种，平均物种数由79.6种减少到52.1种（减少34.4%）.江湖阻隔后鱼类群落的功能性状和功能多样性指数发生了显著变化，洄游性鱼类（包括河海洄游和江湖洄游）物种占比（由39.7%降至32.6%）和鱼食性物种占比（由31.1%降至25.2%）显著下降，而非洄游性物种占比（由60.3%升至67.5%）和浮游生物食性物种占比（由13.5%升至15.5%）显著上升.连续型性状中，平均营养级（由3.14降至3.10）显著下降、平均生长速率（由0.57 a^-1升至0.65 a^-1）显著上升.阻隔后的物种数（SR）、功能丰富度指数、功能离散度指数和功能分散指数显著低于阻隔前.本研究表明江湖阻隔后鱼类群落不仅物种丰富度下降，且功能性状趋向同质化（或单一化）发展，致使功能多样性下降.研究结果可为东部平原湖泊的渔业资源管理及湖区生态修复和保护提供重要的理论依据.;The eastern plain lake area is the most concentrated area of freshwater lakes in China, supporting numerous lakes, including China's five largest freshwater lakes. However, human activities such as disconnecting lakes from the mainstream are seriously threatening the aquatic biodiversity in the region. In this study, 9 lakes in the eastern plain were selected to study the temporal (before and after the river-lake disconnection) changes in functional traits (3 groups of categorical traits and 6 continuous traits) and functional diversity index of fish assemblages. The results showed that the total number of fish species across the 9 lakes decreased from 140 species to 100 species through time, and the average species richness per lake decreased from 79.6 to 52.1 (accounting for 34.4% of historical species). The functional trait composition and diversity indices of fish communities changed significantly before and after the river-lake disconnection. The percentages of migratory (from 39.7% to 32.6%) and piscivorous species (from 31.1% to 25.2%) significantly decreased, while the percentages of non-migratory (from 60.3% to 67.5%) and planktivorous species (from 13.5% to 15.5%) significantly increased. For the continuous traits, the average trophic level (from 3.14 to 3.10) significantly decreased but the average growth rate (from 0.57 a^-1 to 0.65 a^-1) significantly increased. Species richness, FRic, FDiv and FDis all significantly decreased. These results indicated that, after river-lake disconnection, fish assemblages experienced not only a decrease in species richness but also homogenization (or simplification) trend of functional trait composition and decline in functional diversity. Our study provided scientific background for the ecological protection and restoration of eastern plain lakes in China.