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1. Most studies addressing the causes of the recent increases and expansions of mesopredators in many ecosystems have focused on the top‐down, releasing effect of extinctions of large apex predators. However, in the case of the northward expansion of the red fox into the arctic tundra, a bottom‐up effect of increased resource availability has been proposed, an effect that can counteract prey shortage in the low phase of the multi‐annual rodent cycle. Resource subsidies both with marine and with terrestrial origins could potentially be involved.

2. During different phases of a multi‐annual rodent cycle, we investigated the seasonal dynamics and spatial pattern of resource use by red foxes across a coast to inland low arctic tundra gradient, Varanger Peninsula, Norway. We employed two complementary methods of diet analyses: stomach contents and stable isotope analysis.

3. We found that inland red foxes …