Terrestrial invertebrates provide important prey subsidies to many stream fishes. Non-native invertebrates are widespread in many ecosystems, yet they have received little attention in studies of subsidies to stream food webs. We sampled coastal basins in Big Sur, California, to determine the importance of non-native isopods and other terrestrial invertebrates in the summer diet of steelhead/rainbow trout (Oncorhynchus mykiss) and to estimate the density of isopods along streambanks. Terrestrial invertebrates contributed more than 40% of the energetic value of O. mykiss stomach contents at most sites and up to 75% at some locations. Non-native isopods Armadillidium vulgare or Porcellio scaber occurred at all sites, reaching mean densities of up to 13 individuals/m² on streambanks, and accounted for up to 20% of the energy in the diet. The proportion of non-native isopods in the diet was positively correlated with their density at a site, and the frequency and energetic value of terrestrial invertebrates and non-native isopods in O. mykiss diets increased with fish size. In terms of the broader diet, the energetic value and taxonomic composition of stomach contents varied among sites but there was no major geographic pattern or trend to the variation, and overall O. mykiss diets were generally similar across the region. Our results highlight that non-native terrestrial invertebrates may provide a considerable but overlooked subsidy to stream fishes.

中文翻译：

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非本地等足类动物和其他陆地猎物资源对加利福尼亚州大苏尔沿海溪流中的硬头鳟/虹鳟鱼 Oncorhynchus mykiss 的重要性

陆生无脊椎动物为许多溪流鱼类提供重要的猎物补贴。非本地无脊椎动物广泛存在于许多生态系统中，但它们在对流食物网的补贴研究中很少受到关注。我们在加利福尼亚州大苏尔的沿海盆地取样，以确定非本地等足类动物和其他陆生无脊椎动物在钢头鳟鱼 / 虹鳟鱼 ( Oncorhynchus mykiss )夏季饮食中的重要性，并估计沿河岸等足类动物的密度。在大多数地点，陆生无脊椎动物贡献了O. mykiss胃内容物能量值的 40%以上，在某些地点高达 75%。非本地等足类动物Armadillidium v​​ulgare或Porcellio scaber发生在所有地点，在河岸上的平均密度高达 13 只/m ²，占饮食中高达 20% 的能量。饮食中非本地等足类动物的比例与其在一个地点的密度呈正相关，并且O. mykiss饮食中陆生无脊椎动物和非本地等足类动物的频率和能量值随着鱼的大小而增加。就更广泛的饮食而言，胃内容物的能量价值和分类组成因地点而异，但没有主要的地理模式或变化趋势，总体而言O. mykiss该地区的饮食大体相似。我们的研究结果强调，非本地陆生无脊椎动物可能为溪流鱼类提供可观但被忽视的补贴。