Can Reindeer Overabundance Cause a Trophic Cascade?
- Rolf A. ImsAffiliated withDepartment of Biology, University of TromsøDepartment of Arctic Ecology, NINA, Polar Environmental Centre Email author
- , Nigel G. YoccozAffiliated withDepartment of Biology, University of TromsøDepartment of Arctic Ecology, NINA, Polar Environmental Centre
- , Kari Anne BråthenAffiliated withDepartment of Biology, University of Tromsø
- , Per FauchaldAffiliated withDepartment of Biology, University of TromsøDepartment of Arctic Ecology, NINA, Polar Environmental Centre
- , Torkild TveraaAffiliated withDepartment of Arctic Ecology, NINA, Polar Environmental Centre
- , Vera HausnerAffiliated withDepartment of Biology, University of Tromsø
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The region Finnmark, in northernmost Europe, harbors dense populations of semi-domestic reindeer of which some exhibit characteristics of overabundance. Whereas overabundance is evident in terms of density-dependent reductions in reindeer body mass, population growth and abundance of forage plants, claims have been made that this reindeer overabundance also has caused a trophic cascade. These claims are based on the main premise that reindeer overgrazing negatively impacts small-sized, keystone tundra herbivores. We tested this premise by a large-scale study in which the abundance of small rodents, hares and ptarmigans was indexed across reindeer management districts with strong differences in stocking densities. We examined the scale-dependent relations between reindeer, vegetation and these small-sized herbivores by employing a spatially hierarchical sampling design within the management districts. A negative impact of reindeer on ptarmigan, probably as a result of browsing reducing tall Salix, was indicated. However, small rodents (voles and lemmings), which are usually the keystone herbivores in the plant-based tundra food web, were not negatively impacted. On the contrary, there was a strong positive relationship between small rodents and reindeer, both at the scale of landscape areas and local patches, with characteristics of snow-bed vegetation, suggesting facilitation between Norwegian lemmings and reindeer. We conclude that the recent dampening of the vole and lemming population cycle with concurrent declines of rodent predators in northernmost Europe were not caused by large herbivore overgrazing.
Keywordstundra lemming ptarmigan facilitation food web overgrazing quasi-experiment Salix spatial scaling growth forms
- Can Reindeer Overabundance Cause a Trophic Cascade?
Volume 10, Issue 4 , pp 607-622
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- food web
- spatial scaling
- growth forms
- Author Affiliations
- 1. Department of Biology, University of Tromsø, 9037, Tromsø, Norway
- 2. Department of Arctic Ecology, NINA, Polar Environmental Centre, 9296, Tromsø, Norway