基于多维空间尺度的低头坝对河流鱼类分类多样性和功能多样性的影响研究——以皖南山区为例

Dams have been recognized as one of the primary means by which humans alter fluvial ecosystems. The effects of large dams on stream ecosystems and their abiotic and biotic components have been widely identified. However, how low-head dams modify and alter these ecosystems has received less attention. Till now, the effect of low-head dams on stream fish diversity is still unclear. Our proposal will focus on how low-head dams influence the taxonomic and functional diversity of stream fish assemblages at multiple spatial-scales. The Wannan Mountains will be selected as our study area. The estimation of taxonomic diversity will be based on fish species composition, richness and their abundance. The indexes of functional diversity include functional richness, evenness and divergence, respectively, which will be estimated from the measured morphological variables relating to food acquisition, locomotion and reproduction of fishes. By deliberate site-setting and substantive field-sampling, our proposal will be aimed: 1) at the local scale, to identify how low-head dams alter local habitat conditions and fish taxonomic and functional diversity, and to reveal the associations between the attributes of low-head dams (i.e., dam size, impounding purpose, and spatial position) and their ecological effects; 2) at the watershed scale, to qualify and quantify the influences of low-head dams on the spatial auto-correlation of fish taxonomic and functional diversity within a river network, and to discover whether multiple dams have a cumulative effect on fish diversity; 3) at the regional scale, to discover their independent and combined effect of low-head dams, anthropogenic and natural landscape on fish taxonomic and functional diversity, and to assess whether and how landscape changes modify the ecological effects of low-head dams on fish diversity. Our proposal will bring a scientific base for the conservation, restoration and management of the montane stream ecosystems and fish diversity within this study area and even our country.

水坝是河流生态系统中极具普遍性的一种人类干扰形式。同大型水坝相比，低头坝生态学效应的研究明显不足，低头坝对河流鱼类多样性的影响仍不清楚。本项目以皖南山区为例，基于以物种组成为基础的分类多样性研究与以功能特征（运动、摄食和繁殖）为基础的功能多样性研究，通过周密的样点设置与大量的野外取样，在多维空间尺度上系统地研究低头坝对河流鱼类分类多样性和功能多样性的影响。具体内容包括：1）在局域尺度上，确定低头坝对局域栖息地和鱼类多样性的影响，揭示低头坝的局域生态学效应与水坝属性之间的联系；2）在流域尺度上，确定低头坝如何影响河流网络体中鱼类多样性的空间自相关性，揭示多重低头坝影响鱼类多样性的累积效应；3）在区域尺度上，确定低头坝、人为景观和自然景观对鱼类多样性的独立和联合影响，揭示景观变化如何影响低头坝的生态学效应。为研究区域内、乃至全国的山区河流生态系统及其鱼类多样性的保护、恢复和管理提供科学依据。

低头坝是山区河流系统中普遍存在的一类人为干扰形式。有关低头坝对山区河流的局域栖息地、鱼类多样性的影响仅得到较少的报道。本项目以皖南山区为研究区域，基于以鱼类物种组成为基础的分类多样性研究及以鱼类摄食、运动和繁殖功能特征为基础的功能多样性研究，分别从局域、流域和区域3个空间尺度上系统的研究了低头坝对河流鱼类分类多样性和功能多样性的影响及其生态学机制。经研究发现：（1）在局域尺度上，低头坝影响局域鱼类的分类/功能组成及其多样性的作用模式及其相对重要性主要取决于水坝的蓄水功能（引渠坝 v.s. 蓄水坝）；可能因不同大小水坝的坝上蓄水区的淤积程度不同，水坝大小（依据坝高划分）对低头坝的生态学效应无显著影响。（2）在河流纵向梯度下，低头坝干扰改变了河流中下游自然流态河段的物种组成，导致下游河段α多样性的下降但β多样性的上升，进而改变了自然流态河段鱼类α和β多样性的纵向梯度格局。低头坝驱动了坝上蓄水区河段的栖息地同质化，进而驱动了本地入侵鱼类对土著鱼类的取代过程，但鱼类群落相似性变化取决于初始相似性大小：初始相似性较高时，群落趋于异质化；初始相似性较低时，群落趋于同质化。(3) 在河流网络尺度下，自然流态河段鱼类群落主要受支流空间位置和局域栖息地的联合影响，而陆地景观条件的作用明显较小。坝上蓄水区河段的鱼类物种数主要取决于水坝特征变量（上游水坝数量），而支流位置变量的重要性相对较低；蓄水区土著鱼类群落不仅受底质异质性、水坝坝高等非生物因素的影响，还与入侵鱼类这一生物因素密切相关。（4）在区域尺度下，低头坝驱动了坝上蓄水区鱼类分类和功能组成的变化，其分类组成变化以周转（turnover）过程为主而功能组成变化主要是嵌套（nestedness）过程；该变化过程导致蓄水区分类β多样性的上升，但功能α多样性却显著下降；该变化过程也导致蓄水区鱼类分类和功能相似性的变化，但与上述多样性不同，蓄水区的分类和功能相似性变化具有一致性。