Abstract Non-native crayfish can have impacts on stream communities that are highly variable. A possible explanation for this variability is that crayfish are responding in a context-dependent manner to variation in environmental factors. Among the most critical environmental factors in streams is current velocity. Moving water defines lotic ecosystems and many benthic organisms, including crayfish, respond to its influence. To examine how current velocity affected the impacts of non-native Orconectes rusticus crayfish on benthic communities, we conducted a cage-enclosure experiment in a Wisconsin stream. We hypothesized that current velocities > 50 cm s−1 would decrease the effects that O. rusticus had on community composition (macroinvertebrate richness and numbers) and physical structure (sediment accumulation). Three cage enclosure treatments (open, closed crayfish and closed control) were grouped into eight replicate blocks divided equally among streambed regions of slow (< 50 cm s−1) and fast (> 50 cm s−1) current. Open cages allowed resident crayfish access, closed crayfish cages contained one O. rusticus, and closed controls had no crayfish. After three weeks, crayfish cages had lower macroinvertebrate abundance and richness and less sediment accumulation. Current velocity showed a positive relationship to macroinvertebrates in general, and a negative relationship to sediment build-up. The most common macroinvertebrates were hydropsychid caddisflies that responded to O. rusticus in a context-dependent manner such that cages containing crayfish had decreased hydropsychid numbers in fast current, but not in slow. Open cage treatments showed a similar pattern, suggesting that natural crayfish densities in the stream were also sufficient for lowering hydropsychid numbers in fast current. Our study demonstrates that current velocity may provide an important context for understanding the effects that O. rusticus have on benthic communities, not just in terms of what these crayfish do, but how the benthic communities respond to their presence.

中文翻译：

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溪流是否会改变小龙虾对底栖群落的影响？

摘要 非本地小龙虾会对高度可变的溪流群落产生影响。这种可变性的一个可能解释是，小龙虾以依赖于环境的方式对环境因素的变化做出反应。溪流中最关键的环境因素是流速。流动的水定义了激流生态系统，许多底栖生物，包括小龙虾，都会对其影响做出反应。为了检查当前速度如何影响非本地 Orconectes rusticus 小龙虾对底栖群落的影响，我们在威斯康星州的一条溪流中进行了笼罩实验。我们假设当前速度 > 50 cm s−1 会降低 O. rusticus 对群落组成（大型无脊椎动物的丰富度和数量）和物理结构（沉积物积累）的影响。三种网箱围栏处理（开放式、封闭式小龙虾和封闭式对照）被分成八个重复块，在缓慢（< 50 cm s-1）和快速（> 50 cm s-1）流的河床区域之间平均分配。开放式笼子允许常住小龙虾进入，封闭式小龙虾笼子包含一只 O. rusticus，封闭式对照没有小龙虾。三周后，小龙虾网箱的大型无脊椎动物丰度和丰富度较低，沉积物积累较少。水流速度总体上与大型无脊椎动物呈正相关，与沉积物堆积呈负相关。最常见的大型无脊椎动物是以一种依赖于环境的方式对 O. rusticus 做出反应的水螟石蛾，因此装有小龙虾的笼子在快流中会减少水螟数量，但在慢速时不会。开放式网箱处理显示出类似的模式，表明溪流中的天然小龙虾密度也足以降低快速水流中的水灵数量。我们的研究表明，当前的速度可能为理解 O. rusticus 对底栖群落的影响提供了重要的背景，不仅仅是这些小龙虾的行为，而且底栖群落如何响应它们的存在。