ИСТИНА

The winter on the Arctic tundra is a challenging season for predators as severe weather conditions are combined with lack of live prey. Thus most carnivorous species present utilize carcasses as food sources and can be defined as facultative scavengers. Our main objective was to analyze the spatial and temporal distribution of scavengers (i.e. guild structure) within and among field sites with different climates and food web structure. The structure of such guild is important since it can provide feedback on ecosystem processes. A total of four field sites (two in Russia (Yamal and Nenetsky) and two in Norway (Svalbard and Varanger)) were equipped with automatic cameras on carcasses. In terms of bioclimatic zones these sites form a gradient from sub-Arctic (Varanger) to low-Arctic (Yamal and Nenetsky) and high Arctic (Svalbard). Pictures were taken automatically every 10th minute with day and time information. There was an overall gradient in species richness of carnivores following the subarctic-high arctic gradient among the four sites. While only 2 scavenger species were recorded in high-arctic Svalbard (i.e. Arctic fox and Glaucous gull; both of which are genuine arctic), sub-arctic Varanger harbored in total 10 species (most of which have their core distribution further south). Species richness in the two low arctic sites in Yamal and Nenetsky was intermediate with 5 and 4 species, respectively. The numerical dominance relations among the most widely distributed species (i.e. arctic fox, red fox and raven) differed much among sites. For instance, arctic fox was numerically dominant in all sites except Varanger. In the latter site red fox was most common among the mammals, whereas raven was overwhelmingly dominant considering the whole guild. Since the arctic fox was present on all sites its temporal use of carcasses was compared among the sites. In the low arctic sites in Yamal and Nenetsky Arctic foxes used carcasses quite evenly over the 24 hours a day as opposed to Varanger and Svalbard where they were most active during the night and twilight. These differences can be interpreted in terms of risk of inter-guild predation (Varanger) and anthropogenic disturbance (Svalbard).