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  • 1. Aguirre, A. A.
    et al.
    Angerbjörn, A.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Mörner, T.
    Health evaluation of arctic fox (Alopex lagopus) cubs in Sweden2000In: Journal of Zoo and Wildlife Medicine, Vol. 31, no 1, p. 36-40Article in journal (Refereed)
    Abstract [en]

    Hematologic. serum biochemistry, and serum cortisol reference ranges were established and tonsil/rectal bacterial and fecal parasite examinations were performed on 21 wild arctic fox (Alopex lagopus) cubs during July 1996. Several of the hematologic and serum biochemistry values fell within normal ranges for other wild canids or domestic dogs of the same age class. Serum alanine transaminase and creatine phosphokinase values were significantly higher in the youngest cubs. Proteus vulgaris and Escherichia coli were isolated from both tonsilar and rectal swabs of several cubs in all dens. The most common gastrointestinal parasite ova were Toxascaris leonina (59%), Isospora spp. (52%), Uncinaria stenocephala (33%), and Capillaria spp. (26%). Prevalence of T. leonina differed significantly between dens and between age groups. Hematologic and serum biochemistry values and degree of parasitism may be indicators of health, stress, and nutritional status of arctic foxes.

  • 2. Aguirre, A. Alonso
    et al.
    Principe, B.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Mörner, Torsten
    Field anesthesia of wild arctic fox (Alopex lagopus) cubs in the Swedish lapland using medetomidine-ketamine-atipamezole2000In: Journal of Zoo and Wildlife Medicine, Vol. 31, no 2, p. 244-246Article in journal (Refereed)
    Abstract [en]

    A safe and effective anesthetic regime for use in arctic fox (Alopex lagopus) cubs was developed. During July 1996, six free-ranging 6-8-wk-old cubs were captured near their den in Vindelfjallen Nature Reserve, Sweden. Medetomidine and ketamine HCl, followed by atipamezole, were selected for the anesthetic trial because of the well-documented safety and efficacy of this drug combination in a broad range of species. The dosage regimen used was 50 mu g/kg medetomidine combined with 2.5 mg/kg ketamine followed by reversal with 250 mu g/kg atipamezole. induction was rapid, with a mean induction time of 1 min and 32 sec (range: 58-150 sec). The cubs were anesthetized for a mean time of 18 +/- 5 min (range: 13-25 min). Serially recorded heart rate, respiratory rate, temperature, and pulse oximetry were stable throughout the anesthetic period for all cubs. Anesthetic depth was suitable for safe handling and minor clinical procedures, including venipuncture. Following atipamezole, all cubs were standing within 12 +/- 7 min (range: 5-24 min) and fully recovered at 27 +/- 5 min (range: 19-36 min). This information will be useful for future captive breeding and management programs involving the endangered arctic fox.

  • 3.
    Ahlgren, Hans
    et al.
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Lidén, Kerstin
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies.
    Multiple prehistoric introductions of the mountain hare (Lepus timidus) on a remote island, as revealed by ancient DNA2016In: Journal of Biogeography, ISSN 0305-0270, E-ISSN 1365-2699, Vol. 43, no 9, p. 1786-1796Article in journal (Refereed)
    Abstract [en]

    Aim: The majority of the non-volant mammals now present on the island of Gotland, Sweden, have been introduced in modern times. One exception is the mountain hare (Lepus timidus), which was present on the island more than 9000 years ago. This paper investigates the origins of the Gotland hares and temporal changes in their genetic structure, and considers how they may have reached the island.

    Location: The island of Gotland, Sweden (57°30′ N, 18°20′ E).

    Methods: Two fragments of the mitochondrial D-loop 130 + 164 base pairs in length from skeletal remains from 40 ancient mountain hares from Gotland, 38 from the Swedish mainland and five from Lithuania were analysed and compared with 90 modern L. timidus haplotypes from different locations in Eurasia and five haplotypes of the Don-hare (Lepus tanaiticus) morphotype.

    Results: The Mesolithic hares from Gotland (7304 bc–5989 bc) cluster with modern hares from Russia, Scotland, the Alps and Fennoscandia whereas the Gotland hares from the Neolithic and onwards (2848 bc–1641 ad) cluster with Neolithic hares from the Swedish mainland and modern hares from Fennoscandia. The Neolithic haplotypes from Lithuania and the Don-hare haplotypes were dispersed within the network. The level of differentiation (FST) between the Mesolithic and Neolithic hares on Gotland was twice as great as that observed on the mainland.

    Main conclusions: The ancient hares on Gotland fall into two haplogroups separated in time, indicating that the mountain hare became extinct at one point, with subsequent re-colonization events. In view of the isolated location of Gotland, it is probable that the hares were brought there by human means of transport.

  • 4.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Body size in island Apodemus populations2007In: Hystrix: The Italian Journal of Mammology, ISSN 1825-5272, Vol. 2, p. 417-Article in journal (Refereed)
  • 5.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Fjällräv (Alopex lagopus).2007In: Artfakta – Rödlistade ryggradsdjur i Sverige., Artdatabanken, Uppsala. , 2007, p. 456-459Chapter in book (Other (popular science, discussion, etc.))
  • 6.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Gigantism in Island Populations of Wood Mice (Apodemus) in Europe1986In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 47, no 1, p. 47-56Article in journal (Refereed)
    Abstract [en]

    Many rodents have large body sizes on islands, and there are many hypotheses that try to explain this observed pattern. Using body size data on Apodemus in Europe as an example, I try to evaluate the main hypotheses. These can be divided in four different categories. 1) Hypotheses assuming climatic differences between islands and mainland: no trend in body size on islands in the Mediterranean, in Britain or in the Baltic area is observed. 2) Hypotheses based on island size: no trend is observed in the data analysed. 3) Hypotheses based on distance to mainland: no general effect is found, although there is an effect in the British material. 4) Hypotheses based on faunistic differences: consistent relationships are found in all areas. A. sylvaticus shows larger body size when lacking competition from A. flavicollis or Clethrionomys glareolus or when predation is absent. A. flavicollis is larger when predators are lacking, and smaller when no competitors are present. This is in agreement with character displacement theory

  • 7.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Mountain Hare Populations on Islands - Effects of Predation by Red Fox1989In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 81, no 3, p. 335-340Article in journal (Refereed)
    Abstract [en]

    On islands off the west coast of Sweden the density of mountain hares (Lepus timidus L.) is very high. One of the main predators on hares, the red fox (Vulpes vulpes L.), is only present during short periods. Data on hare density and predation by red fox and eagle owl (Bubo bubo (L.)) has been analyzed from five islands over several years. Winter mortality in years with low predation pressure was independent of hare density. But when red fox or eagle owl were present on islands (i.e., high predation pressure) winter mortality became density dependent. Thus, at low density, winter mortality did not increase through red fox predation. But at densities up to two hares/ha, predation pressure was increasing and could be limiting for these populations. At still higher hare density predation pressure became less intensive. The functional response for foxes preying on hares showed a type II or a sigmoid type III response pattern. In normal summers, the population increase due to reproduction was at least two-fold. When a fox was present there was instead a sharp decrease in hare numbers. Fox predation had a stronger effect in summer than in winter. By switching between islands and mainland areas from winter to summer, a fox can stabilize fluctuations in hare numbers on the islands. This is dependent on how often the ice permits a fox to reach an island and the lack of numerical response by predators.

  • 8.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    The Effect of Red Fox Predation on Mountain Hare Populations on Islands1986In: Mammal Review, ISSN 0305-1838, E-ISSN 1365-2907, Vol. 16, no 3-4, p. 198-198Article in journal (Refereed)
    Abstract [en]

    The population dynamics of Mountain Hares on islands have been monitored during 10 years. In some years Red Foxes have been present on some islands. The intensity of predation on the hares is given from the reduction of the known hare densities, and from the foxes’ diet (scat analysis). The effect of predation on the hare populations was found to be density dependent, but also dependent on the alternative food available.

    [Complete text from journal]

  • 9.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    The Evolution of Body Size in Mammals on Islands - Some Comments1985In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 125, no 2, p. 304-309Article in journal (Refereed)
  • 10.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Arvidson, Bengt
    Stockholm University, Faculty of Science, Department of Zoology.
    Norén, Erik
    Strömgren, Lasse
    The Effect of Winter Food on Reproduction in the Arctic Fox, Alopex-Lagopus - a Field Experiment1991In: Journal of Animal Ecology, Vol. 60, no 2, p. 705-714Article in journal (Refereed)
    Abstract [en]

    (1) The population of arctic foxes in Fennoscandia is very small and has been so for around 60 years in spite of total protection for over half a century. The reasons why the arctic fox population has not increased to its former size are unknown. The population numbers fluctuate highly in relation to vole numbers. There is also very high interannual variation in reproduction among arctic foxes. (2) To determine the effect of winter food availability on reproductive success, we carried out a feeding experiment. The study area is situated above the treeline from an altitude of 700 m to mountains of 1600 m in Swedish Lapland. We added food (reindeer and moose carcasses) to dens during the winter months, January-April 1985-89. To determine the effect of this extra food on reproduction, we made inventories at both food-manipulated dens and control dens. These inventories of dens took place during July so we could check not only if dens were occupied, but also whether a litter was born and assess the number of cubs appearing outside the den. (3) The proportion of occupied dens in the experimental group was significantly higher than in the control group. The number of cubs at weaning in the food-manipulated dens was also higher than in control dens in each year. However, no effect on litter size was found. (4) From these results we conclude that the larger number of cubs produced in dens with extra winter food shows that reproduction under present dietary poor conditions was limited by available food. Many canid species show this close relation between reproduction and food availability, with pregnancy rates and litter sizes declining with the abundance of the main food.

  • 11.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Börjesson, Patrik
    Stockholm University, Faculty of Science, Department of Zoology.
    Brandberg, K.
    Stable isotope analysis of harbour porpoises and their prey from the Baltic and Kattegat/Skagerrak Seas2006In: Marine Biology Research, ISSN 1745-1000, E-ISSN 1745-1019, Vol. 2, no 6, p. 411-419Article in journal (Refereed)
    Abstract [en]

    The by-caught harbour porpoises in commercial fisheries have raised concerns over their conservation status in the Baltic region. One important aspect for management purposes is porpoise movements within the region. We measured stable isotopes in cod, herring and hagfish, species that are important prey for harbour porpoises in the Baltic region. Bone collagen in fish from the marine Kattegat/Skagerrak was significantly enriched in C-13 compared with collagen in fish from the brackish Baltic Sea. However, despite the isotopic variation seen in their prey, we found no difference in C-13 in harbour porpoise collagen from the two areas. In fact, only eight of 24 porpoises had isotope signatures corresponding to those estimated for the diet in the area where they were caught. Our general conclusion is that porpoises move between the Baltic and Kattegat/Skagerrak Seas. Future studies are needed to evaluate the magnitude of these movements.

  • 12.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Eide, Nina E.
    Dalén, Love
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Hellström, Peter
    Stockholm University, Faculty of Science, Department of Zoology.
    Ims, Rolf A.
    Killengreen, Siw
    Landa, Arild
    Meijer, Tomas
    Stockholm University, Faculty of Science, Department of Zoology.
    Mela, Matti
    Niemimaa, Jukka
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Yoccoz, Nigel G.
    Henttonen, Heikki
    Carnivore conservation in practice: replicatedmanagement actions on a large spatial scale2013In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 50, no 1, p. 59-67Article in journal (Refereed)
    Abstract [en]

    More than a quarter of the world’s carnivores are threatened, often due to multiple andcomplex causes. Considerable research efforts are devoted to resolving the mechanisms behindthese threats in order to provide a basis for relevant conservation actions. However, evenwhen the underlying mechanisms are known, specific actions aimed at direct support for carnivoresare difficult to implement and evaluate at efficient spatial and temporal scales.2. We report on a 30-year inventory of the critically endangered Fennoscandian arctic foxVulpes lagopus L., including yearly surveys of 600 fox dens covering 21 000 km2. These surveysshowed that the population was close to extinction in 2000, with 40–60 adult animalsleft. However, the population subsequently showed a fourfold increase in size.3. During this time period, conservation actions through supplementary feeding and predatorremoval were implemented in several regions across Scandinavia, encompassing 79% of thearea. To evaluate these actions, we examined the effect of supplemental winter feeding andred fox control applied at different intensities in 10 regions. A path analysis indicated that47% of the explained variation in population productivity could be attributed to lemmingabundance, whereas winter feeding had a 29% effect and red fox control a 20% effect.4. This confirms that arctic foxes are highly dependent on lemming population fluctuationsbut also shows that red foxes severely impact the viability of arctic foxes. This study also highlightsthe importance of implementing conservation actions on extensive spatial and temporalscales, with geographically dispersed actions to scientifically evaluate the effects. We note thatpopulation recovery was only seen in regions with a high intensity of management actions.5. Synthesis and applications. The present study demonstrates that carnivore populationdeclines may be reversed through extensive actions that target specific threats. Fennoscandianarctic fox is still endangered, due to low population connectivity and expected climate impactson the distribution and dynamics of lemmings and red foxes. Climate warming is expected tocontribute to both more irregular lemming dynamics and red fox appearance in tundra areas;however, the effects of climate change can be mitigated through intensive managementactions such as supplemental feeding and red fox control.

  • 13.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology.
    Henttonen, Heikki
    Eide, Nina
    NINA.
    Landa, Arild
    NINA.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology.
    Meijer, Tomas
    Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology.
    Progress report 2007 LIFE03 NAT/S/000073 Saving the Endangered Fennoscandian Alopex lagopus SEFALO+.2007Report (Other (popular science, discussion, etc.))
    Abstract [en]

    In total, 36 litters were recorded in Scandinavia during the summer 2007 of which 0 in Finland, 24 inSweden and 15 in Norway. In 2001 and 2004, when the small rodent cycle was in the same increasephase as this year, we had 9 and 28 litters recorded in Scandinavia, respectively, which means thatthe population has increased strongly during the last six years. However, the population increase hasnot been similar all over Scandinavia. In the southern mountain areas, Helagsfjällen and Borgafjäll,the actions of feeding and red fox removal have been very efficient. The number of litters in theseareas has doubled between each rodent increase year. The Norwegian part of Børgefjell has acted asa control area where no actions have been implemented. There, the number of litters has remainedconstant in increase years during the project period 2001-2007. In the northern mountain areas,Vindelfjällen and areas in Norrbotten, we have not managed to keep a high intensity of actions. Thenumber of litters in these areas has been stable. The reasons for the large variation in extent ofimplemented actions between the mountain areas are mainly logistical problems due to the extent ofthe geographical areas concerned in combination with harsh winter climate. In the northern areas,due to the geographical distances, field workers would have to stay in the field for several days inorder to perform field actions which can be achieved in a single day in the southern mountain areas.

  • 14.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Hersteinsson, P.
    Liden, Kerstin
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies, Archaeological Research Laboratory. Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution.
    Nelson, E.
    Dietary Variation in Arctic Foxes (Alopex-Lagopus) - an Analysis of Stable Carbon Isotopes1994In: Oecologia, Vol. 99, no 3-4, p. 226-232Article in journal (Refereed)
    Abstract [en]

    We used stable carbon isotopes to analyse individual variation in arctic fox diet. We extracted collagen from bones (the lower jaw), and measured stable carbon isotopes. The foxes came from three different localities: Iceland, where both microtines and reindeer are rare; west Greenland, where microtines are absent; and Sweden, where seat analyses showed the primary food to be microtine rodents and reindeer. The Icelandic samples included foxes from both coastal and inland habitats, the Swedish sample came from an inland area, and the Greenland sample from coastal sites. The spatial variation in the isotopic pattern followed a basic division between marine and terrestrial sources of protein. Arctic foxes from inland sites had delta(13)C values of -21.4 (Ice land) and -20.4 parts per thousand (Sweden), showing typical terrestrial values. Coastal foxes from Greenland had typical marine Values of -14.9 parts per thousand, whereas coastal foxes from Iceland had intermediate values of -17.7 parts per thousand. However, there was individual variation within each sample, probably caused by habitat heterogeneity and territoriality among foxes. The variation on a larger scale was related to the availability of different food items. These results were in accordance with other dietary analyses based on seat analyses. This is the first time that stable isotopes have been used to reveal individual dietary patterns. Our study also indicated that isotopic values can be used on a global scale.

  • 15.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Hjernquist, B.
    A Rapid Summer Decline in a Mountain Hare Population on an Island1984In: Acta Theriologica, ISSN 0001-7051, E-ISSN 2190-3743, Vol. 29, no 1-10, p. 63-75Article in journal (Refereed)
  • 16.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Pehrson, A.
    Factors Influencing Winter Food Choice by Mountain Hares (Lepus-Timidus L) on Swedish Coastal Islands1987In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 65, no 9, p. 2163-2167Article in journal (Refereed)
    Abstract [en]

    In mainland areas, mountain hares seem unable to survive on a single browse species. However, mountain hares on islands off the west coast of Sweden rely almost entirely on a plain heather diet during winter. Herein, we give as a possible explanation for this phenomenon that the high concentration of sodium in the heather in the coastal areas can buffer the high sodium excretion otherwise observed in hares feeding on heather under experimental conditions. Furthermore, hares selected heather with the highest nitrogen and phosphorus contents. We argue that the pattern of food choice exhibited by the hares in the coastal area is to be expected in homogenous habitats where hares rely on one dominant food species. In heterogenous habitats, the possibility of food selection on a nutritional level is to a considerable extent overridden by effects of digestibility and concentration of secondary compounds in the different food plants available.

  • 17.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, M.
    Stockholm University, Faculty of Science, Department of Zoology.
    Bjärvall, A.
    Ericson, M.
    From, J.
    Noren, E.
    Dynamics of the Arctic Fox Population in Sweden1995In: Annales Zoologici Fennici, Vol. 32, no 1, p. 55-68Article in journal (Refereed)
    Abstract [en]

    Arctic fox populations fluctuate widely with the abundance of prey, i.e. lemmings and voles (Arvicolinae). We have investigated the patterns and mechanisms of these fluctuations in arctic fox numbers through den inventories during 20 years (1974-1993) in Sweden. Time series analyses confirmed a four-year cyclicity in both arctic fox numbers and litter size. However, the different geographical regions were not in synchrony. The fox population in the southern parts of the distribution range has shown regular peaks during the whole period, whereas those in the northern and middle parts of Sweden have declined since 1982. In the northernmost county, also litter sizes have decreased. These differences coincided with an absence of vole and lemming peaks in the north. Experimental feeding confirmed that food availability had a direct impact on breeding success and litter size, thereby limiting the population. We conclude that the total number of arctic foxes in Sweden in 1994 is as low as 40-80 animals.

  • 18.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Erlinge, S.
    Predator-prey relationships: Arctic foxes and lemmings1999In: Journal of Animal Ecology, Vol. 68, no 1, p. 34-49Article in journal (Refereed)
    Abstract [en]

    1. The number of breeding dens and litter sizes of arctic foxes Alopex lagopus were recorded and the diet of the foxes was analysed during a ship-based expedition to 17 sites along the Siberian north coast. At the same time the cyclic dynamics of coexisting lemming species were examined. 2. The diet of arctic foxes was dominated by the Siberian lemming Lemmus sibiricus (on one site the Norwegian lemming L. lemmus), followed by the collared lemming Dicrostonyx torquatus. 3. The examined Lemmus sibiricus populations were in different phases of the lemming cycle as determined by age profiles and population densities. 4. The numerical response of arctic foxes to varying densities of Lemmus had a time lag of 1 year, producing a pattern of limit cycles in lemming-arctic fox interactions, Arctic fox litter sizes showed no time lag, but a linear relation to Lemmus densities. We found no evidence for a numerical response to population density changes in. Dicrostonyx. 5. The functional or dietary response of arctic foxes followed a type II curve for Lemmus, but a type III response curve for Dicrostonyx. 6. Arctic foxes act as resident specialist for Lemmus and may increase the amplitude and period of their population cycles. For Dicrostonyx, on the other hand, arctic foxes act as generalists which suggests a capacity to dampen oscillations.

  • 19.
    Angerbjörn, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Lundberg, Håkan
    Stockholm University, Faculty of Science, Department of Zoology.
    Geographical and temporal patterns of lemming population dynamics in Fennoscandia2001In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 24, no 3, p. 298-308Article in journal (Refereed)
    Abstract [en]

    There is a long-lasting debate in ecology on cyclicity, synchrony and time lags of lemming population fluctuations. We have analysed 137 yr of previously published population data on the Norwegian lemming Lemmus lemmus in ten geographic regions of Fennoscandia. The dominating pattern was synchronous 4-yr cycles. There was no support for the hypothesis of a north-south gradient in cycle length. However. we found periods of prolonged interruptions in the cyclicity, which were more common in northern areas. Wa found a high degree of synchrony between regions. with only a weak relationship to distance, The observed pattern in lemming population dynamics was more consistent with effects from extrinsic factors, such as climate. than intrinsic factors. such as dispersal.

  • 20.
    Barth, Lukas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Are Norwegian lemmings Lemmus lemmus avoided by arctic Alopex lagopus or red foxes Vulpes vulpes? A feeding experiment2000In: Wildlife Biology, Vol. 6, no 2, p. 101-109Article in journal (Refereed)
    Abstract [en]

    Arctic fox Alopex lagopus and red fox Vulpes vulpes are close relatives with similar niche demands in the Holarctic. Where they are sympatric, they compete for territories, dens and food. Seat analyses from Fennoscandia have shown different proportions of lemmings and voles in the diets of the two fox species suggesting food partitioning. However, it was not clear if this was due to different food preferences or distinct habitat use. Since the arctic fox is an endangered species in Fennoscandia, it is important to know whether the superior, north spreading red fox can oust it from the tundra habitat, or if food specialisation may prevent displacement. In a feeding experiment at the Lycksele Zoo in northern Sweden, we compared the food preferences of two arctic and two red foxes. Our results show that the four individuals responded similarly to a variety of food items, and particularly that the two species were not distinct in their food preferences concerning lemmings and voles. However, the foxes had considerable individual predilections. Therefore, in the wild, the unequal proportions of lemmings and voles found in seats may reflect different habitat use for hunting.

  • 21. Berteaux, Dominique
    et al.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Ehrich, Dorothee
    Eide, Nina E
    Fuglei, Eva
    Gallant, Daniel
    Ims, Rolf A
    Kruchenkova, Elena
    Lecomte, Nicholas
    Menuyshina, Irina
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Ovsjanikov, Nikita
    Rodnikova, Anna
    Tarroux, Arnaud
    Yoccoz, Nigel Gilles
    Arctic and red foxes2011In: Arctic WOLVES: Arctic Wildlife Observatories Linking Vulnerable EcoSystems / [ed] Gauthier, G., & D. Berteaux, Quebec City, Quebec, Canada: Centre d’études nordiques, Université Laval , 2011, p. 76-87Chapter in book (Other academic)
  • 22. Berteaux, Dominique
    et al.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Erlandsson, Rasmus
    Stockholm University, Faculty of Science, Department of Zoology.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    White, Paula A.
    Harmonizing circumpolar monitoring of Arctic fox: benefits, opportunities, challenges and recommendations2017In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 36, no suppl. 1, article id 2Article in journal (Refereed)
    Abstract [en]

    The biodiversity working group of the Arctic Council has developed pan-Arctic biodiversity monitoring plans to improve our ability to detect, understand and report on long-term change in Arctic biodiversity. The Arctic fox (Vulpes lagopus) was identified as a target of future monitoring because of its circumpolar distribution, ecological importance and reliance on Arctic ecosystems. We provide the first exhaustive survey of contemporary Arctic fox monitoring programmes, describing 34 projects located in eight countries. Monitored populations covered equally the four climate zones of the species’ distribution, and there were large differences between populations in long-term trends, multi-annual fluctuations, diet composition, degree of competition with red fox and human interferences. Den density, number of active dens, number of breeding dens and litter size were assessed in almost all populations, while projects varied greatly with respect to monitoring of other variables indicative of population status, ecosystem state or ecosystem function. We review the benefits, opportunities and challenges to increased integration of monitoring projects. We argue that better harmonizing protocols of data collection and data management would allow new questions to be addressed while adding tremendous value to individual projects. However, despite many opportunities, challenges remain. We offer six recommendations that represent decisive progress toward a better integration of Arctic fox monitoring projects. Further, our work serves as a template that can be used to integrate monitoring efforts of other species, thereby providing a key step for future assessments of global biodiversity.

  • 23. Berteaux, Dominique
    et al.
    Casajus, Nicolas
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Fuglei, Eva
    Foreword to Supplement 1: research on a polar species-the Arctic fox2017In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 36, article id 1Article in journal (Refereed)
    Abstract [en]

    The Arctic fox has a circumpolar distribution and is intensively studied because it is adapted to extreme environments and influences the ecology of many other species. We introduce here a collection of 12 articles on Arctic fox biology and management. After summarizing the main biological features of the species, we explore the peer-reviewed literature dealing with the Arctic fox through a bibliometric network analysis which identifies clusters of papers sharing a high similarity of cited literature. We visualize with a word cloud analysis 10 clusters comprising 97% of 755 articles published by 1742 authors from 1996-2015. Behavioural and ecological questions, including conservation science, dominate this recent literature. The collection of papers published in the supplement offers an excellent representation of current research dealing with Arctic fox biology and management.

  • 24.
    Bruun, H. H.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Moen, Jon
    Virtanen, Risto
    Grytnes, J. A.
    Oksanen, Lauri
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Effects of altitude and topography on species richness of vascular plants, bryophytes and lichens in alpine communities2006In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 17, no 1, p. 37-46Article in journal (Refereed)
    Abstract [en]

    Question: What is the relationship between species richness of vascular plants, bryophytes and macrolichens, and two important gradients in the alpine environment, altitude and local topography? Location: Northernmost Fennoscandia, 250-152 m a.s.l. corresponding to the range between timberline and mountain top. Methods: The vegetation was sampled in six mountain areas. For each 25 vertical metres, the local topographic gradient from wind-blown ridge to snowbed was sampled in quadrats of 0.8 m x 0.8 m. Patterns in species richness were explored using Poisson regression (Generalized Linear Models). Functional groups of species, i.e. evergreen and deciduous dwarf-shrubs, forbs, graminoids, mosses, hepatics and lichens were investigated separately. Results: Functional groups showed markedly different patterns with respect to both altitude and topography. Species richness of all vascular plants showed a unimodal relationship with altitude. The same was true for graminoids, forbs and lichens analysed separately, but forb richness peaked at Much higher altitudes than total richness. The richness of dwarf-shrubs decreased monotonically with altitude, whereas richness of mosses and liverworts showed an increasing trend. Significant interactions between altitude and local topography were present for several groups. The unimodal pattern for total plant species richness was interpreted in terms of local productivity, physical disturbance, trophic interactions, and in terms of species pool effects. Conclusions: Patterns in local species richness result from the action of two opposing forces: declining species pool and decreasing intensity of competition with altitude.

  • 25.
    Bruun, Hans Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Moen, Jon
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Environmental correlates of meso-scale plant species richness in the province of Harjedalen, Sweden2003In: Biodiversity and Conservation, ISSN 0960-3115, E-ISSN 1572-9710, Vol. 12, no 10, p. 2025-2041Article in journal (Refereed)
    Abstract [en]

    We investigated the species richness of vascular plants at the scale of 5 3 5 km in the Swedish province of Harjedalen, and the relationship between richness and environment. Environmental variables included geographical, altitudinal, topographical, bedrock, soil type, and land-cover descriptors. The species richness was subdivided into groups of species with similar life-form, i.e. trees, dwarf shrubs, hydro- and helophytes, vascular cryptogams, forbs, graminoids, and mountain plants. The data were split at random into two equal subsets. Explanatory models were built by multiple linear regression on the first subset, and the models were validated on the second subset. The total species richness of vascular plants could be explained by sandy and clayey soil, the heterogeneity in bedrock types and the area of acid volcanic bedrock. The model could explain about 46% of the variation in species richness. The richness of trees and hydrophytes tended to decrease with altitude, whereas this was not the case for mountain plants. The latter group occurred frequently at low elevation, but then predominantly along streams and rivers. Clayey soils, sandy soils, and basic volcanic bedrock were the variables most frequently included in the regression models.

  • 26. Bruun, Hans Henrik
    et al.
    Österdahl, Sofia
    Moen, Jon
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Distinct patterns in alpine vegetation around dens of the Arctic fox2005In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 28, no 1, p. 81-87Article in journal (Refereed)
    Abstract [en]

    The arctic fox Alopex lugopus excavates its dens in gravely ridges and hillocks, and creates a local environment quite distinct from the surrounding tundra or heath landscape. In northern Sweden, the vegetation of 18 dens of the arctic fox was investigated, as well as reference areas off the dens but in geologically and topographically similar locations. The species composition showed considerable differences between den and reference areas, with grasses and forbs occurring more abundantly on the dens, and evergreen dwarf-shrubs occurring more in reference areas. The effect of the foxes' activities is thought to be either through mechanical soil disturbance, or through nutrient enrichment via scats, urine, and carcasses. This was expected to result in differences in plant traits with key functional roles in resource acquisition and regeneration, when comparing dens with reference areas. We hypothesised that the community mean of specific leaf area (SLA) would differ if nutrient enrichment was the more important effect, and that seed weight, inversely proportional to seed number per ramet and hence dispersal ability, would differ if soil disturbance was the more important effect. Specific leaf area showed a significant difference, indicating nutrient enrichment to be the most important effect of the arctic fox on the vegetation on its dens. Arctic foxes act as ecosystems engineers on a small scale, maintaining niches for relatively short-lived nutrient demanding species on their dens in spite of the dominance of long-lived ericaceous dwarf-shrubs in the landscape matrix. Thus, foxes contribute to the maintenance of species richness on the landscape level.

  • 27.
    Dalerum, F
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Angerbjörn, A
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Resolving temporal variation in vertebrate diets using naturally occurring stable isotopes.2005In: Oecologia, ISSN 0029-8549, Vol. 144, no 4, p. 647-58Article in journal (Refereed)
  • 28.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Arctic fox (Alopex lagopus) diet in Karupelv valley, East Greenland, during a summer with low lemming density2000In: Arctic, ISSN 0004-0843, E-ISSN 1923-1245, Vol. 53, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    We investigated the diet of arctic foxes (Alopex lagopus) in the Karupelv valley, East Greenland, during the summer of 1997. Despite a low density, lemmings were the most utilized prey, comprising 65.3% of dry fecal weight in fresh feces. This demonstrates the importance of lemming species as prey for arctic foxes all through a lemming cycle. Birds, arctic hare (Lepus arcticus), and insects also contributed to the diet. Arctic fox remains suggested that the foxes had scavenged their own species. Vegetation, muskoxen (Ovibos moschatus), and seal (Phocidae) were found in small amounts. We compared estimates of prey availability and diets of arctic foxes for a coastal area (<10 km from the shore) and an inland area (>10 km from the shore). Abundance of avian prey tended to be higher in the coastal area. Fresh feces indicated a significant overall difference in arctic fox diets between th: coastal and inland areas. Within prey categories, lemmings were significantly more represented in the inland area, while the coastal area had a more diverse diet overall. We also suggest that the existence of arctic foxes in East Greenland is dependent on regular peak years in lemming density.

  • 29.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Resolving temporal variation in vertebrate diets using naturally occurring stable isotopes2005In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Oecologia, Vol. 144, no 4, p. 647-658Article in journal (Refereed)
    Abstract [en]

    Assessments of temporal variation in diets are important for our understanding of the ecology of many vertebrates. Ratios of naturally occurring stable isotopes in animal tissues are a combination of the source elements and tissue specific fractionation processes, and can thus reveal dietary information. We review three different approaches that have been used to resolve temporal diet variation through analysis of stable isotopes. The most straightforward approach is to compare samples from the same type of tissue that has been sampled over time. This approach is suited to address either long or short-term dietary variation, depending on sample regime and which tissue that is sampled. Second, one can compare tissues with different metabolic rates. Since the elements in a given tissue have been assimilating during time spans specific to its metabolic rate, tissues with different metabolic rates will reflect dietary records over different periods. Third, comparisons of sections from tissues with progressive growth, such as hair, feathers, claws and teeth, will reveal temporal variation since these tissues will retain isotopic values in a chronological order. These latter two approaches are mainly suited to address questions regarding intermediate and short-term dietary variation. Knowledge of tissue specific metabolic rates, which determine the molecular turnover for a specific tissue, is of central importance for all these comparisons. Estimates of isotopic fractionation between source and measured target are important if specific hypotheses regarding the source elements are addressed. Estimates of isotopic fractionation, or at least of differences in fractionation between tissues, are necessary if different tissues are compared. We urge for more laboratory experiments aimed at improving our understanding of differential assimilation of dietary components, isotopic fractionation and metabolic routing. We further encourage more studies on reptiles and amphibians, and generally more studies utilizing multiple tissues with different turnover rates.

  • 30.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Oviedo, Spain; University of Pretoria, South Africa.
    Dalén, Love
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Fröjd, Christina
    Lecomte, Nicolas
    Lindgren, Åsa
    Meijer, Tomas
    Stockholm University, Faculty of Science, Department of Zoology.
    Pečnerová, Patrícia
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Spatial variation in Arctic hare (Lepus arcticus) populations around the Hall Basin2017In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 40, no 10, p. 2113-2118Article in journal (Refereed)
    Abstract [en]

    Arctic environments have relatively simple ecosystems. Yet, we still lack knowledge of the spatio-temporal dynamics of many Arctic organisms and how they are affected by local and regional processes. The Arctic hare (Lepus arcticus) is a large lagomorph endemic to high Arctic environments in Canada and Greenland. Current knowledge about this herbivore is scarce and the temporal and spatial dynamics of their populations are poorly understood. Here, we present observations on Arctic hares in two sites on north Greenland (Hall and Washington lands) and one adjacent site on Ellesmere Island (Judge Daly Promontory). We recorded a large range of group sizes from 1 to 135 individuals, as well as a substantial variation in hare densities among the three sites (Hall land: 0 animals/100 km(2), Washington land 14.5-186.7 animals/100 km(2), Judge Daly Promontory 0.18-2.95 animals/100 km(2)). However, pellet counts suggested that both Hall land and Judge Daly Promontory hosted larger populations at other times. We suggest that our results could have been caused by three spatially differentiated populations with asynchronous population fluctuations. With food limitation being a likely driver behind the observed variation, we argue that food limitation likely interacts with predation and competition in shaping the spatial dynamics of Arctic hares in this region.

  • 31.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Oviedo, Spain; University of Pretoria, South Africa.
    Freire, S.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Lecomte, N.
    Lindgren, A.
    Meijer, Tomas
    Stockholm University, Faculty of Science, Department of Zoology.
    Pečnerová, Patricia
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Dalén, Love
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Exploring the diet of arctic wolves (Canis lupus arctos) at their northern range limit2018In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 96, no 3, p. 277-281Article in journal (Refereed)
    Abstract [en]

    The grey wolf (Canis lupus Linnaeus, 1758) is one of the most widespread large carnivores on Earth, and occurs throughout the Arctic. Although wolf diet is well studied, we have scant information from high Arctic areas. Global warming is expected to increase the importance of predation for ecosystem regulation in Arctic environments. To improve our ability to manage Arctic ecosystems under environmental change, we therefore need knowledge about Arctic predator diets. Prey remains in 54 wolf scats collected at three sites in the high Arctic region surrounding the Hall Basin (Judge Daly Promontory, Ellesmere Island, Canada, and Washington Land and Hall Land, both in northwestern Greenland) pointed to a dietary importance of arctic hare (Lepus arcticus Ross, 1819; 55% frequency of occurrence) and muskoxen (Ovibos moschatus (Zimmermann, 1780); 39% frequency of occurrence), although we observed diet variation among the sites. A literature compilation suggested that arctic wolves (Canis lupus arctos Pocock, 1935) preferentially feed on caribou (Rangifer tarandus (Linnaeus, 1758)) and muskoxen, but can sustain themselves on arctic hares and Greenland collared lemmings (Dicrostonyx groenlandicus (Traill, 1823)) in areas with limited or no ungulate populations. We suggest that climate change may alter the dynamics among wolves, arctic hare, muskoxen, and caribou, and we encourage further studies evaluating how climate change influences predator-prey interactions in high Arctic environments.

  • 32.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Oviedo, Spain; University of Pretoria, South Africa.
    Hellström, Peter
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Miranda, M.
    Nyström, Jesper
    Stockholm University, Faculty of Science, Department of Zoology.
    Ekenstedt, Johan
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Network topology of stable isotope interactions in a sub-arctic raptor guild2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 182, no 2, p. 511-518Article in journal (Refereed)
    Abstract [en]

    Predation is an ecologically important process, and intra-guild interactions may substantially influence the ecological effects of predator species. Despite a rapid expansion in the use of mathematical graph theory to describe trophic relations, network approaches have rarely been used to study interactions within predator assemblages. Assemblages of diurnal raptors are subject to substantial intra- and interspecific competition. Here we used the novel approach of applying analyzes based on network topology to species-specific data on the stable isotopes C-13 and N-15 in feathers to evaluate patterns of relative resource utilization within a guild of diurnal raptors in northern Sweden. Our guild consisted of the golden eagle (Aquila chrysaetos), the gyrfalcon (Falco rusticolus), the peregrine falcon (Falco peregrinus) and the rough-legged buzzard (Buteo lagopus). We found a modular trophic interaction structure within the guild, but the interactions were less nested than expected by chance. These results suggest low redundancy and hence a strong ecological importance of individual species. Our data also suggested that species were less connected through intra-guild interactions than expected by chance. We interpret our results as a convergence on specific isotope niches, and that body size and different hunting behaviour may mediate competition within these niches. We finally highlight that generalist predators could be ecologically important by linking specialist predator species with disparate dietary niches.

  • 33.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kunkel, K.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Shults, B. S.
    Diet of wolverines (Gulo gulo) in the western Brooks Range, Alaska2009In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 28, no 2, p. 246-253Article in journal (Refereed)
    Abstract [en]

    Migratory caribou herds are an important component of the North American tundra. We investigated the wolverine (Gulo gulo) diet in the migratory range of the Western Arctic Caribou Herd in north-western Alaska. Within this area, caribou are absent or occur at low densities for large parts of the year, and thus show a strong seasonality in abundance. Analyses of stomach and colon contents suggested that wolverines primarily consumed caribou during the winter, and that the dietary dependence was related more to caribou mortality than to caribou abundance in the area. We also found indications that wolverines may switch between moose and caribou during periods of low caribou abundance, but that such a switch did not affect wolverine body condition. Our results thus support previous observations that wolverines primarily consume ungulates. However, a better knowledge of how alternative food sources are utilized will be necessary to predict the dietary and demographic responses of wolverines to variations in caribou abundance. We also suggest that further efforts should be made to investigate the effects of other ungulate-dependent predators on wolverine feeding ecology, because such predators may function both as competitors and as suppliers of carrion for scavenging.

  • 34. Dalerum, Fredrik
    et al.
    Kunkel, Kyran
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology.
    Shults, Brad
    Patterns of δ13C and δ15N in wolverine (Gulo gulo) tissues from the Brooks Range, Alaska.2009In: Current Zoology, Vol. 55, p. 188-192Article in journal (Refereed)
    Abstract [en]

    Knowledge of carnivore diets is essential to understand how carnivore populations respond demographically to variations in prey abundance. Analysis of stable isotopes is a useful complement to traditional methods of analyzing carnivore diets. We used data on d13C and d15N in wolverine tissues to investigate patterns of seasonal and annual diet variation in a wolverine (Gulo gulo) population in the western Brooks Range, Alaska, USA. The stable isotope ratios in wolverine tissues generally reflected that of terrestrial carnivores, corroborating previous diet studies on wolverines. We also found in variation in d13C and d15N both between muscle samples collected over several years as well as between tissues with different assimilation rates, even after correcting for isotopic fractionation. This suggests both annual and seasonal diet variation. Our results indicate that data on d13C and d15N holds promise for qualitative assessments of wolverine diets changes over time. Such temporal variation may be important indicators of ecological responses to environmental perturbations, and we suggest that more refined studies of stable isotopes may be an important tool when studying temporal change in diets of wolverines and similar carnivores.

  • 35. Dalerum, Fredrik
    et al.
    Perbro, Anna
    Stockholm University, Faculty of Science, Department of Zoology.
    Magnusdottir, Rannveig
    Hersteinsson, Pall
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    The influence of coastal access on isotope variation in Icelandic arctic foxes2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 3, p. e32071-Article in journal (Refereed)
    Abstract [en]

    To quantify the ecological effects of predator populations, it is important to evaluate how population-level specializations are dictated by intra-versus inter-individual dietary variation. Coastal habitats contain prey from the terrestrial biome, the marine biome and prey confined to the coastal region. Such habitats have therefore been suggested to better support predator populations compared to habitats without coastal access. We used stable isotope data on a small generalist predator, the arctic fox, to infer dietary strategies between adult and juvenile individuals with and without coastal access on Iceland. Our results suggest that foxes in coastal habitats exhibited a broader isotope niche breadth compared to foxes in inland habitats. This broader niche was related to a greater diversity of individual strategies rather than to a uniform increase in individual niche breadth or by individuals retaining their specialization but increasing their niche differentiation. Juveniles in coastal habitats exhibited a narrower isotope niche breadth compared to both adults and juveniles in inland habitats, and juveniles in inland habitats inhabited a lower proportion of their total isotope niche compared to adults and juveniles from coastal habitats. Juveniles in both habitats exhibited lower intra-individual variation compared to adults. Based on these results, we suggest that foxes in both habitats were highly selective with respect to the resources they used to feed offspring, but that foxes in coastal habitats preferentially utilized marine resources for this purpose. We stress that coastal habitats should be regarded as high priority areas for conservation of generalist predators as they appear to offer a wide variety of dietary options that allow for greater flexibility in dietary strategies.

  • 36.
    Dalerum, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Becker, Dennis
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Distribution, morphology and use of arctic fox dens in Sweden2002In: Wildlife Biology, Vol. 8, no 3, p. 185-192Article in journal (Refereed)
    Abstract [en]

    Seventy-seven arctic fox dens in Vindelfjällen, Northern Sweden, are described with regard to distribution, morphology and fox use. The density of dens in the area was 1 den / 21 km2 and dens were more spaced than random. The dens were situated at a mean altitude ( sd) of 915  74 m.a.s.l., were on average 3.5  1.88 km from nearest tree line, had a mean number of 44  32 den openings and a mean area of 277  237 m2. During the 21 year study period, 31 dens were used by arctic foxes and 10 by red foxes. Number of den openings, den area, altitude and distance to nearest tree line explained 36 % of arctic fox den use (p < 0.001) and 21 % of red foxes use of arctic fox dens during the study period (p = 0.01). Arctic foxes used dens at higher altitude (p = 0.03) and further away from forest than red foxes did (p = 0.03), and tended to breed in dens with more den openings (p = 0.08). Arctic foxes used some breeding dens more frequently than others (p = 0.002). Among the breeding dens, both den use and litter size were positively related to den area (den use: p = 0.04; litter size: p < 0.001). Successful breeding dens for arctic foxes in Sweden thus appear to be characterised by large size and many openings, and they are situated far away from forest at relatively high altitudes.

  • 37.
    Dalén, Love
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    DNA analysis on fox faeces and competition induced niche shifts2004In: Molecular Ecology, ISSN 0962-1083, Vol. 13, no 8, p. 2389-2392Article in journal (Refereed)
    Abstract [en]

    Interference competition can force inferior competitors to change their distribution patterns. It is, however, possible that the dominant competitor poses a higher threat during certain times of the year, for example during reproduction. In such cases, the inferior competitor is expected to change its distribution accordingly. We used a molecular species identification method on faeces to investigate how the spatial overlap between arctic and red foxes changes between seasons. The results show that arctic and red foxes are sympatric during winter, but allopatric in summer as arctic foxes retreat to higher altitudes further from the tree-line during the breeding season

  • 38.
    Dalén, Love
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Fuglei, Eva
    Hersteinsson, Pall
    Kapel, Christion M.O.
    Roth, James D.
    Samelius, Gustaf
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Population history and genetic structure of a circumpolar species: the arctic fox2005In: Biological Journal of the Linnean Society, ISSN 0024-4066, E-ISSN 1095-8312, Vol. 84, no 1, p. 79-89Article in journal (Refereed)
    Abstract [en]

    The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements. Thus, it differs from many temperate taxa that were subjected to cyclical restriction in glacial refugia during the Ice Ages. We investigated population history and genetic structure through mitochondrial control region variation in 191 arctic foxes from throughout the arctic. Several haplotypes had a Holarctic distribution and no phylogeographical structure was found. Furthermore, there was no difference in haplotype diversity between populations inhabiting previously glaciated and unglaciated regions. This suggests current gene flow among the studied populations, with the exception of those in Iceland, which is surrounded by year-round open water. Arctic foxes have often been separated into two ecotypes: ‘lemming’ and ‘coastal’. An analysis of molecular variance suggested particularly high gene flow among populations of the ‘lemming’ ecotype. This could be explained by their higher migration rate and reduced fitness in migrants between ecotypes. A mismatch analysis indicated a sudden expansion in population size around 118 000 BP, which coincides with the last interglacial. We propose that glacial cycles affected the arctic fox in a way opposite to their effect on temperate species, with interglacials leading to short-term isolation in northern refugia.

  • 39.
    Dalén, Love
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Götherström, Anders
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies, Archaeological Research Laboratory.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Identifying species from pieces of faeces2004In: Conservation Genetics, ISSN 1566-0621, E-ISSN 1572-9737, Vol. 5, no 1, p. 109-111Article in journal (Refereed)
  • 40.
    Dalén, Love
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Götherström, Anders
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies, Archaeological Research Laboratory.
    Tannerfeldt, Magnus
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Is the endangered Fennoscandian arctic fox (Alopex lagopus) population genetically isolated?2002In: Biological Conservation, Vol. 105, no 2, p. 171-178Article in journal (Refereed)
    Abstract [en]

    The arctic fox population in Fennoscandia is on the verge of going extinct after not being able to recover from a severe bottleneck at the end of the 19th century. The Siberian arctic fox population, on the other hand, is large and unthreatened. In order to resolve questions regarding gene flow between, and genetic variation within the populations, a 294 bp long part of the mitochondrial hypervariable region 1 was sequenced. This was done for 17 Swedish, 15 Siberian and two farmed foxes. Twelve variable nucleotide sites were observed, which resulted in 10 different haplotypes. Three haplotypes were found in Sweden and seven haplotypes were found in Siberia. An analysis of molecular variance showed a weak, but significant, differentiation between the populations. No difference in haplotype diversity was found between the populations. A phylogenetic analysis revealed that the three Swedish haplotypes were not monophyletic compared to the Siberian haplotypes. These results indicate a certain amount of gene flow between the two populations. both before and after the bottleneck. Restocking the Fennoscandian population with arctic foxes from Siberia might therefore be a viable option.

  • 41.
    Dalén, Love
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kvaloy, K.
    Linnell, J. D. C.
    Elmhagen, Bodil
    Stockholm University, Faculty of Science, Department of Zoology.
    Strand, O.
    Tannerfeldt, M.
    Henttonen, H.
    Fuglei, E.
    Landa, A.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Population structure in a critically endangered arctic fox population: does genetics matter?2006In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 15, no 10, p. 2809-2819Article in journal (Refereed)
    Abstract [en]

    The arctic fox (Alopex lagopus) in Scandinavia is classified as critically endangered after having gone through a severe decline in population size in the beginning of the 20th century, from which it has failed to recover despite more than 65 years of protection. Arctic foxes have a high dispersal rate and often disperse over long distances, suggesting that there was probably little population differentiation within Scandinavia prior to the bottleneck. It is, however, possible that the recent decline in population size has led to a decrease in dispersal and an increase in population fragmentation. To examine this, we used 10 microsatellite loci to analyse genetic variation in 150 arctic foxes from Scandinavia and Russia. The results showed that the arctic fox in Scandinavia presently is subdivided into four populations, and that the Kola Peninsula and northwest Russia together form a large fifth population. Current dispersal between the populations seemed to be very low, but genetic variation within them was relatively high. This and the relative F-ST values among the populations are consistent with a model of recent fragmentation within Scandinavia. Since the amount of genetic variation is high within the populations, but the populations are small and isolated, demographic stochasticity seems to pose a higher threat to the populations' persistence than inbreeding depression and low genetic variation.

  • 42.
    Dalén, Love
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Nyström, Veronica
    Stockholm University, Faculty of Science, Department of Zoology.
    Valdiosera, Cristina
    Germonpre, Mietje
    Sablin, Mikhail
    Turner, Elaine
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Arsuaga, Juan Luis
    Götherström, Anders
    Ancient DNA reveals lack of postglacial habitat tracking in the arctic fox2007In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 104, no 16, p. 6726-6729Article in journal (Refereed)
    Abstract [en]

    How species respond to an increased availability of habitat, for example at the end of the last glaciation, has been well established. In contrast, little is known about the opposite process, when the amount of habitat decreases. The hypothesis of habitat tracking predicts that species should be able to track both increases and decreases in habitat availability. The alternative hypothesis is that populations outside refugia become extinct during periods of unsuitable climate. To test these hypotheses, we used ancient DNA techniques to examine genetic variation in the arctic fox (Alopex lagopus) through an expansion/contraction cycle. The results show that the arctic fox in midlatitude Europe became extinct at the end of the Pleistocene and did not track the habitat when it shifted to the north. Instead, a high genetic similarity between the extant populations in Scandinavia and Siberia suggests an eastern origin for the Scandinavian population at the end of the last glaciation. These results provide new insights into how species respond to climate change, since they suggest that populations are unable to track decreases in habitat avaliability. This implies that arctic species may be particularly vulnerable to increases in global temperatures.

  • 43.
    Elmhagen, B.odil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    The applicability of metapopulation theory to large mammals2001In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 94, no 1, p. 89-100Article in journal (Refereed)
    Abstract [en]

    Metapopulation theory has become a common framework in conservation biology and it is sometimes suggested that a metapopulation approach should be used for management of large mammals. However. it has also been suggested that metapopulation theory would not be applicable to species with long generations compared to those with short ones. In this paper, we review how and on what empirical ground metapopulation terminology liar, been applied to insects, small mammals and large mammals, The review showed that the metapopulation term sometimes was used for population networks which only fulfilled the broadest possible definition of a metapopulation, i.e. they were subpopulations connected by migrating individuals. We argue that the metapopulation concept should be reserved for networks that also show some kind of metapopulation dynamics. Otherwise it applies to almost all populations and loses its substance. We found much empirical support for metapopulation dynamics in both insects and small mammals, but not in large mammals. A me possible reason is the methods used to confirm the existence of metapopulation dynamics, For insects and small mammals, the common approach is to study population turnover through patch occupancy data. Such data is difficult to obtain for large mammals, since longer temporal scales need to be covered to record extinctions and colonizations. Still, many populations of large mammals are exposed to habitat fragmentation and the resulting subpopulations sometimes have high risks of extinction. If there is migration between the subpopulations, the metapopulation framework could provide valuable information on their population dynamics. We suggest that a metapopulation approach can be interesting for populations of large mammals. when there are discrete breeding subpopulations and when these subpopulations have different growth rates and demographic fates. Thus, a comparison of the subpopulations' demographic fates, rather than subpopulation turnover, can be a feasible alternative for studies of metapopulation dynamics in large mammals.

  • 44.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Berteaux, Dominique
    Burgess, Robert M.
    Ehrich, Dorothee
    Gallant, Daniel
    Henttonen, Heikki
    Ims, Rolf A.
    Killengreen, Siw T.
    Niemimaa, Jukka
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Ollila, Tuomo
    Rodnikova, Anna
    Sokolov, Alexandrs A.
    Sokolova, Natasha A.
    Stickney, Alica A.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Homage to Hersteinsson and Macdonald: climate warming and resource subsidies cause red fox range expansion and Arctic fox decline2017In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 36, no suppl. 1, article id 3Article, review/survey (Refereed)
    Abstract [en]

    Climate change can have a marked effect on the distribution and abundance of some species, as well as their interspecific interactions. In 1992, before ecological effects of anthropogenic climate change had developed into a topical research field, Hersteinsson and Macdonald published a seminal paper hypothesizing that the northern distribution limit of the red fox (Vulpes vulpes) is determined by food availability and ultimately climate, while the southern distribution limit of the Arctic fox (Vulpes lagopus) is determined by interspecific competition with the larger red fox. This hypothesis has inspired extensive research in several parts of the circumpolar distribution range of the Arctic fox. Over the past 25 years, it was shown that red foxes can exclude Arctic foxes from dens, space and food resources, and that red foxes kill and sometimes consume Arctic foxes. When the red fox increases to ecologically effective densities, it can cause Arctic fox decline, extirpation and range contraction, while conservation actions involving red fox culling can lead to Arctic fox recovery. Red fox advance in productive tundra, concurrent with Arctic fox retreat from this habitat, support the original hypothesis that climate warming will alter the geographical ranges of the species. However, recent studies show that anthropogenic subsidies also drive red fox advance, allowing red fox establishment north of its climate-imposed distribution limit. We conclude that synergies between anthropogenic subsidies and climate warming will speed up Arctic ecosystem change, allowing mobile species to establish and thrive in human-provided refugia, with potential spill-over effects in surrounding ecosystems.

  • 45.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Borgström, Sara
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Boyd, Emily
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. University of Reading, England.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Dalen, Love
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ermold, Matti
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hedlund, Johanna
    Stockholm University, Faculty of Science, Department of Zoology.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Jaramillo, Fernando
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lagerholm, Vendela K.
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Moor, Helen
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Nykvist, Björn
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Stockholm University, Stockholm Environment Institute.
    Pasanen-Mortensen, Marianne
    Stockholm University, Faculty of Science, Department of Zoology.
    Plue, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Prieto, Carmen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    van der Velde, Ype
    Stockholm University, Faculty of Science, Department of Physical Geography. Wageningen University & Research Center, Netherlands.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Interacting effects of change in climate, human population, land use, and water use on biodiversity and ecosystem services2015In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 20, no 1, article id UNSP 23Article in journal (Refereed)
    Abstract [en]

    Human population growth and resource use, mediated by changes in climate, land use, and water use, increasingly impact biodiversity and ecosystem services provision. However, impacts of these drivers on biodiversity and ecosystem services are rarely analyzed simultaneously and remain largely unknown. An emerging question is how science can improve the understanding of change in biodiversity and ecosystem service delivery and of potential feedback mechanisms of adaptive governance. We analyzed past and future change in drivers in south-central Sweden. We used the analysis to identify main research challenges and outline important research tasks. Since the 19th century, our study area has experienced substantial and interlinked changes; a 1.6 degrees C temperature increase, rapid population growth, urbanization, and massive changes in land use and water use. Considerable future changes are also projected until the mid-21st century. However, little is known about the impacts on biodiversity and ecosystem services so far, and this in turn hampers future projections of such effects. Therefore, we urge scientists to explore interdisciplinary approaches designed to investigate change in multiple drivers, underlying mechanisms, and interactions over time, including assessment and analysis of matching-scale data from several disciplines. Such a perspective is needed for science to contribute to adaptive governance by constantly improving the understanding of linked change complexities and their impacts.

  • 46.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Eide, Nina E.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Killengreen, Siw T.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Wallén, Johan
    Stockholm University, Faculty of Science, Department of Zoology.
    Åtgärdsprogram för fjällräv, 2017–2021 (Vulpes lagopus): Hotkategori: Starkt hotad EN2017Report (Other academic)
  • 47.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Hellström, Peter
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Kindberg, Jonas
    Changes in vole and lemming fluctuations in northern Sweden 1960-2008 revealed by fox dynamics2011In: Annales Zoologici Fennici, ISSN 0003-455X, E-ISSN 1797-2450, Vol. 48, no 3, p. 167-179Article in journal (Refereed)
    Abstract [en]

    Cyclic dynamics with extensive spatial synchrony has long been regarded as characteristic of key herbivores at high latitudes. This contrasts to recent reports of fading cycles in arvicoline rodents in boreal and alpine Fennoscandia. We investigate the spatio-temporal dynamics of boreal red fox and alpine arctic fox in Sweden as a proxy for the dynamics of their main prey, voles and Norwegian lemming, respectively. We analyse data from five decades, 1960-2008, with wavelets and autocorrelation approaches. Cyclic dynamics were identified with at least one method in all populations (arctic fox n = 3, red fox n = 6). The dynamics were synchronous between populations, or coupled with a 1-yr lag, in 8 of 13 pairwise comparisons. Importantly though, the dynamics were heterogeneous in space and time. All analytical approaches identified fading cycles in the three arctic fox populations and two northern red fox populations. At least one method identified similar patterns in three southern red fox populations. Red fox dynamics were cyclic in the 1970s primarily, while arctic fox dynamics was cyclic until the late 1980s or early 1990s. When cyclic, 4-yr cycles dominated in arctic fox and northern red fox, whilst 3-4-yr cycles was found in southern red foxes. Significant cyclic regimes reappeared in the 1990s or 2000s in two red fox populations and one arctic fox population. Cycles and regionally coupled dynamics appeared associated in northern arctic and red foxes. This study supports accumulating evidence which suggests that cyclic and synchronous patterns in the dynamics of lemmings and voles are nonstationary in space and time. Furthermore, the similar patterns of change in both fox species indicate that persistence of cycles is governed by similar mechanisms in lemmings and voles.

  • 48.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Hersteinsson, Páll
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Unnsteinsdottir, Ester R.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    From breeding pairs to fox towns: the social organisation of arctic fox populations with stable and fluctuating availability of food2014In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 37, no 1, p. 111-122Article in journal (Refereed)
    Abstract [en]

    Food availability can impact group formation in Carnivora. Specifically, it has been suggested that temporal variation in food availability may allow a breeding pair to tolerate additional adults in their territory at times when food abundance is high. We investigate group occurrence and intraspecific tolerance during breeding in a socially flexible canid, the arctic fox (Vulpes lagopus). We compare Iceland and Sweden where resource conditions differ considerably. A breeding pair was the most common social unit in both populations, but as predicted, groups were more frequent where food abundance varied substantially between years (Sweden: 6 %) than where food availability was stable (Iceland: ≤2 %). Within Sweden, supplemental feeding increased group occurrence from 6 to 21 %, but there was no effect of natural variation in lemming (Lemmus lemmus) availability since group formation was rare also at lemming highs. Thus, additional factors appeared to influence the trade-off between intraspecific territoriality and tolerance. We report two cases where related females showed enduring social relationships with good-neighbour strategies. Related females also engaged in alloparental behaviour in a ‘fox town’ with 31 foxes (4 adults, 3 litters). In contrast, when unrelated foxes bred close to each other, they moved or split their litters during summer, presumably because of territorial conflict. We suggest that fluctuating food availability is linked to group formation in this Arctic carnivore, but also when food availability increases, additional factors such as relatedness, alloparental benefits, competition and predator defence appear necessary to explain group formation.

  • 49.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kindberg, Jonas
    Hellström, Peter
    Stockholm University, Faculty of Science, Department of Zoology.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    A boreal invasion in response to climate change?: Range shifts and community effects in the borderland between forest and tundra2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, no 1, p. 39-50Article in journal (Refereed)
    Abstract [en]

    It has been hypothesized that climate warming will allow southern species to advance north and invade northern ecosystems. We review the changes in the Swedish mammal and bird community in boreal forest and alpine tundra since the nineteenth century, as well as suggested drivers of change. Observed changes include (1) range expansion and increased abundance in southern birds, ungulates, and carnivores; (2) range contraction and decline in northern birds and carnivores; and (3) abundance decline or periodically disrupted dynamics in cyclic populations of small and medium-sized mammals and birds. The first warm spell, 1930-1960, stands out as a period of substantial faunal change. However, in addition to climate warming, suggested drivers of change include land use and other anthropogenic factors. We hypothesize all these drivers interacted, primarily favoring southern generalists. Future research should aim to distinguish between effects of climate and land-use change in boreal and tundra ecosystems.

  • 50.
    Elmhagen, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tannerfeldt, M.
    Angerbjörn, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Food-niche overlap between arctic and red foxes2002In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 80, no 7, p. 1274-1285Article in journal (Refereed)
    Abstract [en]

    Arctic foxes (Alopex lagopus) in Fennoscandia have retreated to higher altitudes on the mountain tundra, possibly because of increased competition with red foxes (Vulpes vulpes) at lower altitudes. In this study we compare summer food niches of the two species in mountain tundra habitat. Arctic foxes consumed lemmings more often than red foxes did, while red foxes consumed field voles and birds more often. Yet despite substantial variation in the diet of each species among summers, food-niche overlaps between the species were consistently high in most summers, as arctic and red foxes responded similarly to temporal changes in prey availability. Occurrences of field voles and birds in fox scats were negatively Correlated with altitude, while the occurrences of lemmings tended to increase with altitude. Since arctic foxes bred at higher altitudes than red foxes, the differences between arctic and red fox diets were better explained by altitudinal segregation than by differences between their fundamental food niches. Arctic foxes should therefore endeavour to use the more productive hunting grounds at the lower altitudes of their former range, but interference competition with red foxes might decrease their access to these areas, and consequently cause a decrease in the size of in their realised niche.

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