Background

The treeless mountain tundra found along the Swedish-Norwegian border in Scandinavia constitutes a southwestern extension of the Russian arctic tundra, with species such as arctic foxes Alopex lagopus, reindeer Rangifer tarandus and Norwegian lemmings Lemmus lemmus. The arctic fox was much hunted in the early 20th century due to is valuable fur and the population declined rapidly. Despite protection in Sweden and Norway since 1928 and 1930 respectively, it never recovered. Present population estimates for Scandinavia total about 100 adult individuals. Increased competition with the larger red fox Vulpes vulpes is one factor which may have had an adverse effect on the arctic fox population and hampered its recovery. The red fox has a food niche very similar to that of the arctic fox; when it settles in an arctic fox habitat, it may monopolise the most productive areas, as it is dominant over arctic foxes in direct conflicts over e.g. dens and carcasses (Frafjord et al., 1989, Elmhagen et al., 2002). Furthermore, the red fox is a predator on arctic fox cubs and may occasionally kill even adult arctic foxes. As a consequence arctic foxes seem to avoid contact with red foxes, in particular during reproduction (Tannerfeldt et al., 2002, Dalén et al., 2004). The fact that red foxes have become more numerous in productive mountain tundra areas may therefore explain why the arctic fox has retreated to the less productive, high-altitude parts of its former Scandinavian range in the 20th century (Dalerum et al., 2002, Elmhagen et al., 2002). The competitive relationship between arctic and red foxes in Scandinavia is by no means unique among predators. Interspecific killing, i.e. individuals of one species killing those of another, is quite common among mammalian carnivores (Palomares and Caro, 1999). The risk of predation combined with competition can cause individuals of the inferior, usually the smaller, species to change their use of habitat and activity patterns. For example, it has been shown that coyotes Canis latrans avoid the larger wolf Canis lupus and that red foxes avoid both the larger coyote and the Iberian lynx Lynx pardinus (Harrison et al. 1989, Thurber et al. 1992, Fedriani et al., 1999). Over the last centuries, many populations of large mammalian predators have either been reduced or gone extinct. Decreased predation and competition from large predators may lead to increased densities of medium-sized predators. This may in turn have negative effects on species diversity through increased predation on smaller prey species (Crooks and Soulé, 1999). The Scandinavian red fox population increased dramatically between 1930 and 1960 (Lindström, 1989). At the same time there was a northward spread of red foxes in North America and Siberia (Marsh 1938, Chirkova 1968). Possible reasons for this range expansion are large-scale processes such as increased productivity due to climate change and/or decreased predation and competition from declining populations of wolves and lynx (Lindström, 1989, Hersteinsson and Macdonald, 1992). The red fox is thus becoming an important medium-sized predator in tundra habitats and this may have important ecological consequences. The largest effect should be seen on the arctic fox, but due to its larger size the red fox may also be a more severe predator on reindeer calves and geese than the arctic fox is.

Aims

The objective of this project was to investigate the role of medium-sized predators, mainly arctic and red foxes, in a terrestrial arctic ecosystem in Chukotka, Russia. The Scandinavian mountain tundra has only a remnant population of arctic foxes which is very close to extinction. It is also a disturbed ecosystem with small populations of large carnivores. In comparison the predator community in Chukotka is relatively intact and it contains both arctic and red foxes. Thus interactions between these species, as well as interactions between foxes and larger predators, should be more frequent in Chukotka. The Beringia 2005 expedition was therefore a unique opportunity to test hypotheses on species relationships. Arctic and red fox food niches should be similar in Chukotka, as they were in Scandinavia, and the species should therefore have similar habitat preferences in the absence of competition. However, being the dominant competitor, the red fox should mainly be found in relatively productive habitats. On the other hand arctic foxes should avoid confrontation with red foxes and be more numerous in relatively barren habitats, but use the more productive ones when red foxes were scarce or absent. We aimed to test these hypotheses by comparisons of arctic and red fox diets, habitat use and population densities in different areas.

Fieldwork

The fieldwork was carried out in July and August on leg 2C Anadyr of Beringia 2005. We planned to use occurrences of breeding dens and faecal droppings of each species to estimate population density, and the locations of dens and droppings to test patterns of habitat use. The faeces would also be used for later analyses of predator diets and DNA analyses would be used to determine which fox species had deposited the faecal droppings. At each study site we therefore searched the landscape on foot for fox dens and droppings, a method that had previously been used on the Swedish-Russian Tundra Ecology expedition 1994 and on Tundra Northwest 1999. Foxes often scent mark by defecating on elevated structures in the landscape, for example small mounds and peaks, and we therefore searched such places systematically. Fox dens are often covered by lush vegetation resulting from years of fertilisation by faeces and prey remains. Consequently we also looked for and visited such lush patches in the landscape.

During surveys we cooperated with the project of Anders Angerbjörn, whose participants also needed to cover large areas on foot. For reasons of security we always worked in pairs, but co-operation between projects implied that two pairs did surveys each field day, and this enabled us to cover larger areas. To compare diets with prey availability we also needed information on what small rodent species were available and in what densities. These data were also collected in co-operation with Angerbjörn’s project and rodents were snap-trapped at each study site.

We worked at four study sites overall. The first was located in and close to the mountain range south of the wetland plains surrounding Anadyr. The second was situated on coastal tundra close to Anadyr where we took the opportunity to work for a day whilst waiting for transportation to the next site. Sites 3 and 4 were located in the mountain range north of the Anadyr plains. Both this and Angerbjörn’s project needed to survey several areas separated by some distance. As we stayed about one week each at sites 1 and 3, we therefore used every second day to transport ourselves down a river by rubber boats to be able to cover new ground on foot on the days in between transportation.

Preliminary results and future plans

In total we found seven fox dens, of which two were inhabited. We collected single fox scats found elsewhere in the landscape, but fox densities were low. Snap-trapping revealed that rodent densities also were low. Voles and lemmings are generally cyclic in Chukotka, showing pronounced population peaks with some years interval, and we were unfortunate in visiting the region during a cyclic low. A local hunter informed us there were stray wolves in the areas we visited, and we did see wolf tracks during our surveys and collected some wolf scats. There were high densities of brown bears, Ursos arctos, at all study sites and at site 1 in particular. We therefore extended our research plan to also include a diet analysis of brown bears and bear faeces were collected during all surveys.

We did encounter some difficulties during fieldwork. Fox densities were low and we did not find as much fox faeces as we had hoped for. The high bear densities at site 1, in a landscape which to a large extent was covered by dense thickets of pine or broadleaf species, also made work difficult. However thanks to the high bear densities we were able to collect quite a lot of bear faeces, and in co-operation with the projects of Åsa Lindgren and Anders Angerbjörn, who also collected predator faeces, we will continue our work, aiming for a joint paper on predator diets and the role of predators in seed dispersal.