Data from: Contemporary land change alters fish communities in a San Francisco Bay drainage, California, U.S.A.

Urbanization is one of the leading threats to freshwater biodiversity, and urban regions continue to expand globally. Here we examined the relationship between recent urbanization and shifts in stream fish communities. We sampled fishes at 32 sites in the Alameda Creek Watershed, near San Francisco, California, in 1993–1994 and again in 2009, and we quantified univariate and multivariate changes in fish communities between the sampling periods. Sampling sites were classified into those downstream of a rapidly urbanizing area (“urbanized sites”), and those found in less impacted areas (“low-impacted sites”). We calculated the change from non-urban to urban land cover between 1993 and 2009 at two scales for each site (the total watershed and a 3km buffer zone immediately upstream of each site). Neither the mean relative abundance of native fish nor nonnative species richness changed significantly between the survey periods. However, we observed significant changes in fish community composition (as measured by Bray-Curtis dissimilarity) and a decrease in native species richness between the sampling periods at urbanized sites, but not at low-impacted sites. Moreover, the relative abundance of one native cyprinid (Lavinia symmetricus) decreased at the urbanized sites but not at low-impacted sites. Increased urbanization was associated with changes in the fish community, and this relationship was strongest at the smaller (3km buffer) scale. Our results suggest that ongoing land change alters fish communities and that contemporary resurveys are an important tool for examining how freshwater taxa are responding to recent environmental change.

城市化是淡水生物多样性面临的主要威胁之一，且全球城市区域仍在持续扩张。本研究探讨了近期城市化与溪流鱼类群落变化之间的关联。我们于1993—1994年及2009年，在加利福尼亚州旧金山附近的阿拉米达溪流域（Alameda Creek Watershed）的32个采样点开展鱼类采样，并量化了两次采样期间鱼类群落的单变量与多变量变化。我们将采样点划分为两类：一是快速城市化区域下游的"城市化影响采样点"，二是受人类活动干扰较低的"低干扰采样点"。我们针对每个采样点，在两种空间尺度下计算了1993年至2009年间非城市土地向城市土地的覆盖变化：即全流域尺度，以及每个采样点上游紧邻的3千米缓冲带尺度。两次调查期间，本土鱼类的平均相对丰度与外来物种丰富度均未发生显著变化。然而，在城市化影响采样点中，我们观测到鱼类群落组成（以布赖斯-柯蒂斯相异度（Bray-Curtis dissimilarity）衡量）发生了显著变化，且本土物种丰富度出现下降；而低干扰采样点则未出现此类变化。此外，城市化影响采样点中，一种本土鲤科鱼类——对称拉文鱼（Lavinia symmetricus）的相对丰度出现下降，而低干扰采样点未出现该现象。城市化水平提升与鱼类群落变化存在关联，且该关联在更小尺度（3千米缓冲带尺度）下表现最为显著。本研究结果表明，持续进行的土地利用变化会改变鱼类群落，而当代重访采样是探究淡水生物类群对近期环境变化响应的重要手段。