Lemming predators on the Siberian tundra

In the Eurasian Arctic, the most common lemming species are the Siberian le mming (Lemmus sibiricus) and the collared lemming (Dicrostonyx torquatus). Lemmings constitute the main food item for 5 common predators in the area: arctic fox; snowy owl; rough-legged buzzard; long-tailed skua; and pomarine skua. Hence, these predators form a foraging guild. We have studied factor s influencing the structure of this guild. When comparing cooccurrence of t he predators between 17 sites across Siberia, there were positive associati ons between the snowy owl and the two skuas, and a negative association bet ween snowy owl and rough-legged buzzard. There was also a large variation i n local population density among the predators, conceivably, due to the ris k of intra-guild predation as well as the variation in food supply. There w ere significant relationships between lemming abundance and the abundance o f each predator. An analysis of the predatory response by the arctic fox in dicated a response pattern similar to that of a delayed numerical response to lemming abundance. For this and other reasons, we propose that the arcti c fox is a resident specialist predator on microtine rodents. Further, the birds appeared to be nomadic specialist predators with, perhaps, one except ion, the rough-legged buzzard.