Despite low species diversity and primary production, trophic structure (e.g., top predator species, predator size) is surprisingly variable among Arctic lakes. We investigated trophic structure in lakes of arctic Alaska containing arctic char Salvelinus alpinus using stomach contents and stable isotope ratios in two geographically-close but hydrologically-distinct lake clusters to investigate how these fish may interact and compete for limited food resources. Aside from different lake connectivity patterns (‘leaky’ versus ‘closed’), differing fish communities (up to five versus only two species) between lake clusters allowed us to test trophic hypotheses including: (1) arctic char are more piscivorous, and thereby grow larger and obtain higher trophic positions, in the presence of other fish species; and, (2) between arctic char size classes, resource polymorphism is more prominent, and thereby trophic niches are narrower and overlap less, in the absence of other predators. Regardless of lake cluster, we observed little direct evidence of arctic char consuming other fishes, but char were larger (mean TL = 468 vs 264 mm) and trophic position was higher (mean TP = 4.0 vs 3.8 for large char) in lakes with other fishes. Further, char demonstrated less intraspecific overlap when other predators were present whereas niche overlap was up to 100% in closed, char only lakes. As hydrologic characteristics (e.g., lake connectivity, water temperatures) will change across the Arctic owing to climate change, our results provide insight regarding potential concomitant changes to fish interactions and increase our understanding of lake trophic structure to guide management and conservation goals.

尽管物种多样性低和初级生产，但是营养结构（例如顶级捕食者的物种，捕食者的大小）在北极湖泊之间却出乎意料地变化。我们调查了含有北极红点鲑Salvelinus alpinus的北极阿拉斯加湖泊的营养结构利用两个地理上相近但水文上截然不同的湖泊群中的胃内容物和稳定的同位素比率，来研究这些鱼如何相互作用并竞争有限的食物资源。除了不同的湖泊连通性模式（“泄漏”与“封闭”）外，湖群之间不同的鱼类群落（多达五种而只有两种）使我们能够检验营养假说，其中包括：（1）北极红点鲑更具鱼食性，因此在其他鱼类的存在下长大并获得更高的营养位置；（2）在北极的火炭大小类别之间，资源多态性更加突出，因此在没有其他捕食者的情况下，营养小生境更窄且重叠更少。不论湖团如何，我们几乎都没有观察到北极炭烧掉其他鱼类的直接证据，但在其他鱼类的湖泊中，炭黑较大（平均TL = 468 vs 264 mm），营养位置较高（大型炭黑平均TP = 4.0 vs 3.8）。此外，当存在其他捕食者时，炭黑表现出较少的种内重叠，而在封闭的仅炭黑的湖泊中，生态位重叠高达100％。由于气候变化，整个北极的水文特征（例如，湖泊连通性，水温）将发生变化，因此我们的结果提供了有关鱼类相互作用潜在伴随变化的见识，并加深了我们对湖泊营养结构的了解，以指导管理和保护目标。当存在其他捕食者时，炭黑表现出较少的种内重叠，而在仅炭黑的封闭湖泊中，生态位重叠高达100％。由于气候变化，整个北极的水文特征（例如，湖泊连通性，水温）将发生变化，因此我们的结果提供了有关鱼类相互作用潜在伴随变化的见识，并加深了我们对湖泊营养结构的了解，以指导管理和保护目标。当存在其他捕食者时，炭黑表现出较少的种内重叠，而在仅炭黑的封闭湖泊中，生态位重叠高达100％。由于气候变化，整个北极的水文特征（例如，湖泊连通性，水温）将发生变化，因此我们的结果提供了有关鱼类相互作用潜在伴随变化的见识，并加深了我们对湖泊营养结构的了解，以指导管理和保护目标。