河流鱼类分类群和功能群的纵向梯度格局——以新安江流域为例

确定鱼类群落的空间格局是保护和管理河流鱼类多样性的基础。尽管河流鱼类分类群（基于物种组成）的纵向梯度格局已得到大量报道,但其功能群（基于功能特征）的空间格局研究较少。以皖南山区新安江为研究流域,沿其"正源-下游"梯度共设置27个调查样点,分别于2017年5月和10月完成2次调查取样,着重研究了鱼类分类群和功能群结构的纵向梯度格局及其形成机制。共采集鱼类44种,可分为5个运动功能群和4个营养功能群,构成14个"营养-运动"复合功能群。双因素交互相似性分析结果显示,鱼类分类群和功能群均随河流级别显著变化,但两者均无显著的季节变化;根据相似性百分比分析,由1级至3级河流,数量优势物种和功能群的空间变化主要呈嵌套格局,而由3级至5级河流其变化主要呈周转格局。方差分解结果显示,局域栖息地、陆地景观和支流空间位置3类解释变量对分类群和功能群空间变化的解释率分别为33.6%和38.5%,其中,分类群受局域栖息地和支流空间位置变量的显著影响,而功能群受局域栖息地和陆地景观变量的显著影响。研究表明,沿着新安江的"上游-下游"纵向梯度,鱼类分类群和功能群的空间格局基本一致,但两者的形成机制不同：分类群的纵向梯度变化受环境过滤和扩散过程的联合影响,而功能群则主要受环境过滤影响。

Longitudinal patterns in taxonomic and functional organizations of fish assemblages in the Xin'an River

Identifying spatial patterns is important for the conservation and management of fish diversity in streams. The spatial variation along the upstream-downstream gradient in stream fish assemblages has been substantially investigated previously. However, most investigations have focused on the species-composition-based taxonomic organizations but the species-trait-based functional organizations have received less attention. In this study, we sampled fishes from 27 segments along the upstream-downstream gradient of the Xin''an River during May and October 2017. Our aims were to examine the longitudinal variation in taxonomic and functional assemblages of stream fish assemblages, and to determine the relative importance of local habitat, segment spatial position, and landscape condition on fish assemblage composition. According to the feeding habits and locomotion traits of the fishes, the 44 species collected in this study were divided into four feeding groups, five locomotion groups, and 14 combined feeding-locomotion groups. A two-way crossed ANOSIM showed that both taxonomic and functional organizations differed significantly among the 1^st- to 5^th-order streams, but they did not differ significantly between May and October. According to SIMPER, the spatial patterns of abundance-dominant species and functional guilds were similar along the upstream-downstream gradient. From the 1^st- to 3^rd-order streams, the changes in fish assemblages agreed with the patterns of community nestedness, i.e., small assemblages nested within larger assemblages. However, from the 3^rd- to 5^th-order streams, the changes agreed with patterns of community turnover, i.e., both species/guild loss and gain occurring from one assemblage to another. Variance partitioning showed that all three types of explanatory variables measured (i.e., local habitat, landscape condition, and segment spatial position) explained 33.6% of the spatial variation in taxonomic organizations and 38.5% of the functional organizations. In addition, the taxonomic organizations was significantly affected by the local habitat and segment spatial position; whereas, the landscape condition was less important. The functional organizations were significantly influenced by local habitat and landscape condition, but the segment spatial position variables were less important. Overall, our results suggest that, along the upstream-downstream gradient, both taxonomic and functional organizations of fish assemblages exhibit similar levels of spatial variation. However, spatial variation in taxonomic organizations is driven by both environmental filtering and species dispersal, whereas the functional organizations are mainly determined by environmental filtering.