Structural characteristics of a low Arctic tundra ecosystem and the retreat of the Arctic fox

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Abstract

We conducted a large-scale, campaign-based survey in Finnmark, northern Norway to evaluate the proposition that declining Arctic fox populations at the southern margin of the Arctic tundra biome result from fundamental changes in the state of the ecosystem due to climatic warming. We utilized the fact that the decline of the Arctic fox in Finnmark has been spatially heterogeneous by contrasting ecosystem state variables between regions and landscape areas (within regions) with and without recent Arctic fox breeding.

Within the region of Varanger peninsula, which has the highest number of recorded dens and the most recent breeding records of Arctic fox, we found patterns largely consistent with a previously proposed climate-induced, bottom-up trophic cascade that may exclude the Arctic fox from tundra. Landscape areas surrounding dens without recent Arctic breeding were here more productive than areas with recent breeding in terms of biomass of palatable and climate sensitive plants, the number of insectivorous passerines and predatory skuas. Even the frequency of unspecified fox scats was the highest in landscape areas where arctic fox breeding has ceased, consistent with an invasion of the competitively dominant red fox. The comparisons made at the regional level were not consistent with the results within the Varanger region, possibly due to different causal factors or to deficiencies in Arctic fox monitoring at a large spatial scale. Thus long-term studies and adequate monitoring schemes with a large-scale design needs to be initiated to better elucidate the link between climate, food web dynamics and their relations to Arctic and red foxes.

Introduction

The Arctic is currently subject to changes threatening the integrity of tundra ecosystems (CAFF, 2003). Global warming, which is expected to be most pronounced in polar regions, is particularly highlighted (Callaghan et al., 2004b, Foley, 2005, Hinzman et al., 2005, Chapin et al., 2005). However, climate change takes place in conjunction with several other anthropogenic stressors, such as intensified land use (CAFF, 2003, ACIA, 2004). Although the entire Arctic region may be subject to change, the low Arctic tundra zone (Bliss et al., 1973) may be particularly prone to early and rapid change, because it balances against more southern and vastly different ecosystem states (Epstein et al., 2004).

It has been proposed that upper trophic levels (i.e. predators) may be particularly sensitive to fundamental ecosystem alterations (Schmitz et al., 2003, Sergio et al., 2005, Voigt et al., 2003). Tundra ecosystems have typically a tri-trophic, plant-based food web topped by a guild of predators preying mainly on herbivorous small mammals (lemmings and voles) (Elton, 1942, Wiklund et al., 1999, Krebs et al., 2003, Ims and Fuglei, 2005). Some of these small mammal predators, such as the Arctic fox Alopex lagopus (Angerbjörn et al., 2004, Fuglei, 2005), are found exclusively in the Arctic region and should for this reason be particularly vulnerable to global warming (CAFF, 2003, ACIA, 2004, Callaghan et al., 2004a).

In a seminal paper Hersteinsson and MacDonald (1992) analyzed harvest statistics and demonstrated that the Arctic fox during the last century had exhibited a warming related retreat of from the southern edge of the Arctic. They proposed an underlying process scenario that involved a bottom-up trophic cascade by which a warming-induced increase in primary productivity (i.e. plant biomass) in turn gave way to a higher secondary productivity (i.e. prey biomass) available to the northward expanding red fox expelling the competitive subordinate Arctic fox. Hersteinsson and MacDonald (1992) wrote, however, that they were “mindful” with regard to the exact mechanisms in the paucity of data on variables other than fox harvest rates and climatology. Indeed, in Fennoscandia where the Arctic fox is on the verge of regional extinction, several other explanations for the “Arctic fox problem” have been forwarded (for reviews see Hersteinsson et al., 1989, Angerbjörn et al., 1995, Linnell et al., 1999a). As a result management actions (such as population enhancement by introduction of captive bred Arctic foxes in Norway) are now undertaken that implicitly assume that no fundamental change of the ecosystem underlies the Arctic fox decline.

In the present study, we aim to provide the first direct evaluation of Hersteinsson and McDonald’s proposition that the retreat of the Arctic fox from the southern edge of the Arctic is ultimately due to a climate-induced change in ecosystem structure. We do this by analyzing relevant ecosystem state variables measured during a large-scale, targeted field campaign encompassing regions in eastern Finnmark, northern Norway with current presence or absence of the Arctic fox. According to Hersteinsson and MacDonald (1992) we predicted that tundra areas where arctic fox breeding had ceased should show increased biomass of plants likely have increased under warmer climate and, moreover equivalent responses in variables reflecting higher trophic levels consistent with a bottom-up trophic cascade.

Section snippets

General characteristics of the study area

The region of eastern Finnmark forming the northeastern tip of Norway at 70–71°N, is bio-climatically classified as low Arctic tundra (Walker et al., 2005). The Finnmark tundra, which is most clearly defined on the low-altitude peninsulas bordering the Barents sea (Fig. 1), constitutes the westernmost fringe of the vast Euro-Asian tundra (Virtanen et al., 1999). The study area is low-altitude (<400 m a.s.l.), relatively coast-near tundra. The climate is characterized by relatively mild winters

Plants

For the contrasts between regions, the reference blocks in VARANGER (i.e. the region with most recent Arctic fox breeding) had more bilberry and acrocarp mosses than all the other regions (Fig. 3). Except for a significant higher abundance of dwarf birch and crowberry and less prostrate Salix in VARANGER than in NORDKINN, there were no other clear differences between the reference blocks at the regional level.

Within both regions with known fox dens (i.e. VARANGER and LAKSEFJORD) landscape

Assessing the premises of the Hersteinsson–MacDonald hypothesis

In this study, we assessed whether the geographic presence-absence pattern of Arctic fox in low arctic tundra were associated with differences in ecosystem state variables compatible with the climate-induced, trophic cascade proposed by Hersteinsson and MacDonald (1992). The study area in eastern Finnmark offered a good case for such an assessment being a relatively homogenous area in terms of topography and geography and located at the climatic periphery of the circumpolar tundra biome (

Conclusion

By the present study we have provided a first assessment of whether changes in ecosystem structure according to a proposed climate change scenario proposed by Hersteinsson and MacDonald (1992) could underlie the retreat of the Arctic fox from low arctic tundra. Our analysis relied on data from a spatially extensive, but short-term, campaign-based study. Of course such an approach provides only a snap-shot picture of a highly dynamic system (see Krebs et al., 2003 for a discussion). On the other

Acknowledgements

This project was supported financially by the Norwegian Directorate of Nature Management and the Research Council of Norway. Field assistance was provided by Pieter Beck, Tina Dahl, Ingrid Jensvold, Bjørn Hugo Kristoffersen, Stein Tore Pedersen, Arne Petter Sarre, Guro Saurdal, Cecilie Steffen and Alfred Ørjebu. Comments on the manuscript by Eva Fuglei and two anonymous referees are much appreciated.

References (91)

  • A. Angerbjörn et al.

    Dynamics of the Arctic fox population in Sweden

    Annales Zoologici Fennici

    (1995)
  • A. Angerbjörn et al.

    Predator–prey relationships: Arctic foxes and lemmings

    Journal of Animal Ecology

    (1999)
  • A. Angerbjörn et al.

    Arctic foxes. Consequences of resource predictability in the Arctic fox – two life history strategies

  • Austrheim, G., Mysterud, A., Hassel, K., Evju, M., Økland, R.H., in press. Ecological effects of sheep grazing in a low...
  • G.O. Batzli et al.

    The herbivore-based trophic system

  • L.C. Bliss et al.

    Arctic tundra ecosystems

    Annual Reviews of Ecology and Systematics

    (1973)
  • K.A. Bråthen et al.

    More efficient estimation of plant biomass

    Journal of Vegetation Science

    (2004)
  • M.S. Bret-Harte et al.

    Developmental plasticity allows Betula nana to dominate tundra subjected to an altered environment

    Ecology

    (2001)
  • R.W. Brooker et al.

    Carex bigelowii Torrey ex Schweinitz (C. rigida Good., non Schrank; C. hyperborea Drejer)

    Journal of Ecology

    (2001)
  • H.H. Bruun et al.

    Distinct patterns in alpine vegetation around dens of the Arctic fox

    Ecography

    (2005)
  • CAFF

    Arctic flora and fauna: status and conservation

    (2003)
  • T.V. Callaghan et al.

    Responses to projected changes in climate and UV-B at the species level

    Ambio

    (2004)
  • T.V. Callaghan et al.

    Key findings and extended summaries

    Ambio

    (2004)
  • B.Å. Carlsson et al.

    Impact of climate change factors on the clonal sedge Carex bigelowii: implications for population growth and vegtative spread

    Ecography

    (1994)
  • F.S. Chapin et al.

    Role of land-surface changes in Arctic summer warming

    Science

    (2005)
  • M. Crawley

    Statistics: an introduction using R

    (2005)
  • L. Dalén et al.

    Identifying species from pieces of faeces

    Conservation Genetics

    (2004)
  • F. Dalerum et al.

    Distribution, morphology and use of Arctic fox Alopex lagopus dens in Sweden

    Wildlife Biology

    (2002)
  • S. Dray et al.

    Co-inertia analysis and the linking of ecological data tables

    Ecology

    (2003)
  • L. Edenius et al.

    Combining satellite imagery and ancillary data to map snowbed vegetation important to reindeer Rangifer tarandus

    Arctic AntArctic and Alpine Research

    (2003)
  • P. Ekerholm et al.

    Long-term dynamics of voles and lemmings at the timberline and above the willow limit as a test of hypotheses on trophic interactions

    Ecography

    (2001)
  • Elgvin, D.T., Klingsheim, M., 2002. Sustainable reindeer herding – is it possible (in Norwegian)....
  • B. Elmhagen et al.

    The Arctic fox (Alopex lagopus): an opportunistic specialist

    Journal of Zoology, London

    (2000)
  • B. Elmhagen et al.

    Food-niche overlap between Arctic and red foxes

    Canadian Journal of Zoology

    (2002)
  • C. Elton

    Vole, Mice and Lemmings

    (1942)
  • H.E. Epstein et al.

    The nature of spatial transitions in the Arctic

    Journal of Biogeography

    (2004)
  • J.P. Finerty

    The population ecology of cycles in small mammals

    (1980)
  • J.A. Foley

    Tipping points in the tundra

    Science

    (2005)
  • K. Frafjord

    Do Arctic and red foxes compete for food?

    Zeitschrift für Säugetierkunde

    (2000)
  • D.A. Frank et al.

    Above-ground biomass estimation with the canopy intercept method – a plant growth form caveat

    Oikos

    (1990)
  • E. Fuglei

    Arctic fox

  • G. Gauthier et al.

    Trophic interactions in a high Arctic snow goose colony

    Integrative and Comparative Biology

    (2004)
  • M. Haapasaari

    The oligotrophic heath vegetation of northern Fennoscandia and its zonation

    Acta Botanica Fennica

    (1988)
  • P.A. Hambäck et al.

    Winter herbivory by voles during a population peak: the relative importance of local factors and landscape pattern

    Journal of Animal Ecology

    (1998)
  • I. Hanski et al.

    Predation on competing rodent species: a simple explanation of complex patterns

    Journal of Animal Ecology

    (1996)
  • Cited by (0)

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