人类干扰驱动山区溪流鱼类的分类和功能多样性变化的格局、过程和机制——基于生物同质化理论和方法的研究

Stream systems and lotic fishes are facing multiple threats from environmental changes and anthropogenic disturbances. Identifying the patterns of how stream fishes respond to anthropogenic disturbances is the prerequisite for the conservation and management of fish diversity and stream systems. Although the relationships between stream fish diversity and anthropogenic disturbance have been substantially reported by numerous researchers, most of these researchers used the traditional within-community diversity (i.e., alpha-diversity) of local assemblages to assess the effects of anthropogenic disturbances on fish diversity. As we all know, the traditional alpha-diversity is not available for quantifying the between-community diversity (i.e., beta-diversity) that indicates the ecological processes of fish assemblage changes associated with anthropogenic disturbances, and for assessing the effects of disturbances on the regional biodiversity (i.e., community similarity) of fish assemblages. In this proposal, we will select the montane headwater streams within the Qiantang River as the study area to determine the patterns, processes and mechanisms of the biodiversity changes in stream fish assemblages driven by anthropogenic disturbance. First, using the data collected in headwater streams within the main sub-basins of the Qiantang River, we will survey the backgrounds of species composition and functional traits of fishes in this study area, examine the spatial variations of fish assemblages, and reveal the causes explaining how fish assemblages vary spatially. Second, we will focus on two kinds of anthropogenic disturbances (i.e., low-head dam and land use) that have representativeness for those occurring at this study area. Using the theories and the methods of biotic homogenization, we will assess the effects of anthropogenic disturbances on local habitat, both the taxonomic and functional alpha- and beta-diversity and similarity of fish assemblages. And then, we will determine the patterns (i.e., the changes of both alpha-diversity of local assemblages and community similarity of regional assemblages), ecological processes (i.e., the native-invasive species replacing the endemic species), and mechanisms (i.e., habitat alteration) of the biodiversity changes of stream fish assemblages driven by anthropogenic disturbances. The results of this proposal will bring a scientific basis for the conservation and management of fish diversity in montane streams of this study area.

当前，溪流生态系统及其鱼类多样性正面临着严重威胁；探明溪流鱼类多样性如何响应人类干扰对鱼类物种保护和溪流系统管理至关重要。目前，尽管“溪流鱼类多样性-人类干扰”关系已有大量报道，但大多数研究是以局域群落的物种多寡（α多样性）为研究手段，因而无法量化人类干扰作用下群落组成的变化过程（β多样性）及其对区域群落多样性（群落相似性）的影响。本项目以钱塘江流域为研究区域，在全面调查并厘清其山区河源溪流鱼类的本底组成、空间格局及形成机制的基础上，针对2类极具代表性的人类干扰（即低头坝和土地利用），运用生物同质化的理论和方法系统地调查并研究人类干扰对局域栖息地、鱼类的分类/功能α和β多样性及群落相似性的影响，探明人类干扰驱动鱼类多样性的变化格局（局域群落α多样性及区域群落相似性的变化）及其生态过程（本地入侵种取代土著种）和机制（栖息地变化）。为研究区域内溪流鱼类多样性的保护和管理提供科学依据。

确定溪流鱼类多样性如何响应人类干扰对于溪流鱼类保护和管理至关重要。本项目以新安江流域为研究区域，在厘清区域内溪流鱼类多样性空间格局及其维持机制的基础上，运用生物同质化的理论与方法，系统地研究了人类干扰（低头坝和土地利用）驱动山区溪流鱼类多样性变化的格局、过程和机制。研究结果显示：1）鱼类多样性分布：沿着上游-下游纵向梯度，α多样性和β多样性分别呈钟形和U型分布，尽管分类和功能多样性的空间变化类似，但其生态过程不同（分别由周转过程和嵌套过程主导）；β多样性的纵向梯度空间变异规律受群落配对方法选取影响。2）群落构建机制：集合群落受环境过滤和物种扩散联合影响，但两者的相对重要性随河网空间位置变化；潜在的种间互作在潜在模型中被低估，且对集合群落构建具有调节作用。3）栖息地变化：低头坝坝上蓄水区底质大小和水流流速下降，水宽和水深上升，呈现出栖息地异质化趋势；城镇河段的局域栖息地变化与此类似，且氨氮浓度等指标上升。4）物种组成变化：静水型/耐受性本地入侵种取代亲流型/敏感性土著种，但本地入侵种比率的季节动态显著，且与土地利用强度正相关。5）α多样性变化：土著种α多样性下降，入侵种α多样性上升；分类和功能α多样性对人类干扰的响应可能不一致。6）β多样性变化：低头坝介导下的β多样性空间变异较大，与局域因素和景观因素相关；分类和功能β多样性分别由周转和嵌套主导。7）群落同质/异质化：栖息地异质化导致鱼类群落分类异质化，但功能趋于同质化或无显著变化；同多度相似性相比，组成相似性会低估鱼类群落相似性变化大小；部分配对群落的组成和多度相似性不一致，表现出“视觉同质化/异质化”。8）群落构建机制变化：低头坝可削弱物种扩散在集合群落构建中的作用，进而改变集合群落构建机制。本项目研究结果有助于全面认识人类干扰驱动山区溪流鱼类多样性变化的格局、过程和机制，也为研究区域内鱼类多样性保护提供了科学依据。