水文连通性对西洞庭湖大型底栖动物群落结构的影响

Effects of hydrological connectivity on the community structure of macrobenthos in West Dongting Lake

人为活动干扰纵向与横向水文连通性,对全球景观的生态完整性造成威胁。全球大型河流的洪泛区,包括中国最大的河流长江,都面临着水文连通性下降而造成的生物多样性灾难性损失。了解水文连通性如何影响生物在生境之间的扩散潜力,对于恢复和维持区域和局地生物多样性至关重要。评估了水文连通度对西洞庭湖大型底栖动物群落的影响。沿连通性梯度对54个地点进行了采样,包括河流27个样点,连通湖泊9个样点,阻隔湖泊9个样点和改造洲滩9个样点。结果表明,丰富度,Shannon-wiener指数和Margalef指数等α多样性指数之间存在显着差异(P<0.05),其中连通湖泊与阻隔湖泊的丰富度与丰度较高。连通性最低的改造洲滩α与β多样性最小。更重要的是,丰富度替换是造成河流、连通湖泊和阻隔湖泊中群落组成变化的主要因素,这表明在扩散限制下的中性动态可能是塑造这些生境中底栖动物群落的主要过程。但是,在改造洲滩中,嵌套的重要性很高,可以与丰富度替换相提并论,这反映了在这种不利的环境中,由于生态位分化而导致物种消失的非随机过程。广义线性模型证实,大型底栖动物群落组成空间转换的关键驱动力是水文连通性。研究表明,维持水文连通对于维持洪泛区生态系统的生态完整性至关重要。

Anthropogenic disturbance to natural hydrological connectivity, both longitudinal, lateral, is threatening ecological integrity of many landscapes across the globe. Floodplains of the world′s large rivers, including Yangtze River, the largest river system in China, are facing ecological crisis, such as catastrophic loss of biodiversity due to reduction in hydrological connectivity. Understanding how hydrological connectivity affects dispersal potential of organisms, especially those at lower trophic levels, among habitat patches, is critical for the management of river system aiming to restore and maintain regional and local biodiversity. We evaluated the effect of river-floodplain hydrological connectivity on the macrobenthos assemblage in West Dongting Lake, a Ramsar Wetland that has been threatened mainly by anthropogenic hydrological alternation. We sampled 54 sites along the connectivity gradient from river channels(27 sites), free-connected lakes(9 sites), isolated lakes(9 sites), and modified mudflats(9 sites). Results showed that α diversity indices, including richness, Shannon-weiner index and Margalef index, were significantly different(P<0.05) among different habitats. Connected lakes and isolated lakes had higher richness and abundance. Whereas β diversity generally decreased along the connectivity gradients;and the modified mudflats, with the lowest connectivity, had the smallest overall β diversity. More importantly, richness replacement contributed to majority of variation in community composition in river, connected-and isolated lakes, indicating that neutral dynamics under dispersal limitation might be the main process shaping the macrobenthos communities. However, in modified mudflats, the importance of nestedness was high and comparable to that of richness replacement, reflecting a non-random process of species loss resulted from niche sorting in the less favorable environment. The generalized linear model confirmed that the key driver of the spatial turnover of macro-invertebrate community composition was hydrological connectivity. Our study demonstrated hydrological connectivity is essential for maintaining ecological integrity of floodplain ecosystems.