ARC Centre of Excellence for Environmental Decisions and the NERP Environmental Decisions Hub, School of Botany, University of Melbourne, VIC 3010, Australia.
PLoS One. 2013 Jul 29;8(7):e70262. doi: 10.1371/journal.pone.0070262. Print 2013.
Urbanization affects streams by modifying hydrology, increasing pollution and disrupting in-stream and riparian conditions, leading to negative responses by biotic communities. Given the global trend of increasing urbanization, improved understanding of its direct and indirect effects at multiple scales is needed to assist management. The theory of stream ecology suggests that the riverscape and the surrounding landscape are inextricably linked, and watershed-scale processes will also affect in-stream conditions and communities. This is particularly true for species with semi-aquatic life cycles, such as amphibians, which transfer energy between streams and surrounding terrestrial areas. We related measures of urbanization at different scales to frog communities in streams along an urbanization gradient in Melbourne, Australia. We used boosted regression trees to determine the importance of predictors and the shape of species responses. We then used structural equation models to investigate possible indirect effects of watershed imperviousness on in-stream parameters. The proportion of riparian vegetation and road density surrounding the site at the reach scale (500-m radius) had positive and negative effects, respectively, on species richness and on the occurrence of the two most common species in the area (Criniasignifera and Limnodynastesdumerilii). Road density and local aquatic vegetation interacted in influencing species richness, suggesting that isolation of a site can prevent colonization, in spite of apparently good local habitat. Attenuated imperviousness at the catchment scale had a negative effect on local aquatic vegetation, indicating possible indirect effects on frog species not revealed by single-level models. Processes at the landscape scale, particularly related to individual ranging distances, can affect frog species directly and indirectly. Catchment imperviousness might not affect adult frogs directly, but by modifying hydrology it can disrupt local vegetation and prove indirectly detrimental. Integrating multiple-scale management actions may help to meet conservation targets for streams in the face of urbanization.
城市化通过改变水文条件、增加污染以及破坏溪流和河岸生境来影响溪流，导致生物群落产生负面响应。鉴于全球城市化不断加剧的趋势，需要更好地了解其在多个尺度上的直接和间接影响，以协助管理。溪流生态学理论认为，河流景观和周围的景观是不可分割的，流域尺度上的过程也会影响溪流条件和生物群落。对于具有半水生生命周期的物种（如两栖动物）来说，情况尤其如此，因为这些物种在溪流和周围陆地之间传递能量。我们将不同尺度的城市化措施与澳大利亚墨尔本城市化梯度上溪流中的蛙类群落相关联。我们使用提升回归树来确定预测因子的重要性和物种响应的形状。然后，我们使用结构方程模型来研究流域不透水层对溪流参数的可能间接影响。在河段尺度（500 米半径）上，河岸植被比例和道路密度分别对物种丰富度以及该地区两种最常见物种（Criniasignifera 和 Limnodynastesdumerilii）的出现产生了积极和消极的影响。道路密度和当地水生植被相互作用影响物种丰富度，表明尽管当地栖息地显然良好，但一个地点的隔离可能会阻止其定居。集水区尺度上的不透水层减少对当地水生植被有负面影响，这表明单层次模型无法揭示的对蛙类物种的可能间接影响。景观尺度上的过程，特别是与个体活动范围有关的过程，会直接和间接影响蛙类物种。集水区不透水层可能不会直接影响成蛙，但通过改变水文条件，它可能会破坏当地植被，并间接造成危害。整合多尺度的管理措施可能有助于在城市化背景下实现溪流保护目标。
