| Summary: | Identifying the food resources for a species is one of the basic steps towards understanding population dynamics. The arctic fox is the only terrestrial carnivore on Iceland, and the population had been increasing until recently. Therefore, it is of great importance to know what factors regulate the population growth and which resources support it to understand why the population fluctuates. In this study, stable isotope analysis of arctic fox collagen from Iceland was performed, which revealed what arctic foxes were consuming in their first year of life. The samples used were from 1979 to 2011, period of steady increase of the population. The isotopic signatures were separated between three periods of time (1979-1989, 1990-1999, 2000-2011), two habitats (coastal and inland) and sexes (female and male). The results showed that the diet of young arctic foxes had changed over the study period, as well as a difference in use of resources within and between foxes utilizing different habitats. The results suggested that the main prey items for foxes living in coastal habitats were marine resources while rock ptarmigan was a main resource for inland foxes, even though foxes in both habitats displayed a varied diet. It could be noted that coastal foxes displayed more isotopic changes between periods than inland foxes, and that males living at the coast had more variation on isotopic signatures in comparison with females. From this, it could be suggested that coastal habitats have more availability of different resources and that probably males disperse more than females. These results show how a generalist predator shifts use of resources over the time. Keywords: Vulpes lagopus, arctic fox, stable isotope analysis, diet, Iceland, population dynamics
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