The Swedish Arctic Fox Project

I was employed as a PhD student at the Institute of Zoology - Department of Ecology at Stockholm University with a focus on "Life history characters in the Arctic fox". I investigated the relationship between the evolution of different life history strategies and variable resource availability in arctic foxes (Vulpes lagopus), as well as the impact of climate change. Aim of the study was gaining better understanding of population dynamics at individual level in order to optimize conservation programs to conserve the national population threatened with extinction. As part of the Swedish 'Fjällrävsprojektet ' I coordinated the annual national inventory of the arctic fox population in close cooperation with authorities, rangers and the local (indigenous) population. In addition to applying practical methods (e.g. live traps, telemetry), I gained experience in teaching students.

My project focused on the relationship between the evolution of different life history strategies and variable food availability in arctic foxes (Vulpes lagopus). To do this, I used long-term data on demographics, reproduction, and genetics of two arctic fox ecotypes. The Arctic fox (Latin: Vulpes lagopus, Sw.: Fjällräv, Ger.: Arctic fox) is a small representative of the fox genus. The range extends circumpolarly across the inland tundra and coastal regions of Eurasia, North America and Greenland. The scientific name derives from the Latin vulpes for "fox" and lagopus, which means something like "hare's foot", due to the very hairy feet, similar to the mountain hare.

While the entire stock is classified as not endangered according to the IUCN, the population on the Scandinavian mainland is massively threatened with extinction, despite decades of hunting bans. In addition to the perfect adaptation to extreme temperatures in the arctic regions of the northern hemisphere, they also use their thick fur for camouflage in the snowy and rocky arctic tundra. There are three different color morphs in the wild: white, blue and sand. Furthermore, individuals change their fur color between summer and winter, so the typical white arctic fox can only be found in the gray coat during the summer months.

Single pairs are usually monogamous, raising their offspring in a single burrow between April and September. Adult animals weigh about 2 kilos and live an average of 3 to 4 years, with some animals living up to 10 years. Diet varies greatly with range, but ranges from rodents, birds, fish and reindeer carcasses to berries. Distribution area and diet are the driving factors according to which arctic foxes are divided into two different ecotypes: lemming and coastal ecotypes.

The Scandinavian arctic fox relies primarily on the highly fluctuating, local rodent cycle in the tundra and is therefore referred to as the lemming fox. The lemming (Lemmus spp.) occurs in a regular reproductive cycle spanning 3 to 5 years. The reproductive years are divided into increase, maximum, decrease and minimum. In the fluctuating environment, arctic fox populations must adapt to different optima in their life-history strategies due to temporal variations in resource availability depending on the current phase of the rodent cycle. This creates a fluctuating selection pressure, although most individuals only experience one full cycle in their entire life and are therefore hardly able to react. In contrast, the coastal fox is exposed to a temporally stable resource availability, since the main food source consists of various seabirds (e.g. eider ducks and kittiwakes), fish (e.g. cod), marine invertebrates (e.g. crustaceans and mollusks) and carrion. Thus, in the course of evolution, two different life history strategies have developed as a result of adaptation to fluctuating and stable environmental influences. While the Scandinavian lemming fox populations respond with direct adjustments in litter size between 1 and 18 pups depending on the stage of the rodent cycle without any time lag, Icelandic coastal foxes show little variation in litter size between years.

Collecting data from single individuals of wild carnivore species can be challenging as they are mostly nocturnal and unaccustomed to humans. The Scandinavian arctic fox population has been monitored annually in the summer months since 1980, as the animals become more tolerant of us researchers during this time and, in combination with the bright summer nights, 24-hour surveillance is possible. By individually marking the foxes with colour-coded ear tags, lifelong surveillance of the animals is possible. For this purpose, the arctic foxes are briefly caught, marked and weighed, and a tissue sample is taken to enable genetic analysis. In this way a data series with more than 1000 individuals since 1985 has been created. In addition, we have access to a corresponding dataset from the Icelandic arctic fox population, collected from arctic fox carcasses since 1980.