Changing circumstances : implications for trophic dynamics and species conservation in the Fennoscandian tundra

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Changing circumstances : implications for trophic dynamics and species conservation in the Fennoscandian tundra


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Title: Changing circumstances : implications for trophic dynamics and species conservation in the Fennoscandian tundra
Author: Henden, John-André
Date: 16-Mar-2009
Type: Doctoral thesis; Doktorgradsavhandling
Abstract: A special case of population fluctuation is multi-annual population cycles. While such population cycles exist in several ecosystems, they are more prominent in northern (e.g.tundra) ecosystems, especially among key stone herbivore species. These herbivores providean important ecosystem function in the sense of pulsed flows of resources (i.e. for predators) and disturbances (i.e. for vegetation) throughout the ecosystem. However, the circumstances on the tundra are changing. For instance, large scale collapse of population cycles of many herbivors has been reported, as well as northward expansion of novel predators (e.g. red fox). These changes, heavily connected to climate changes, are capable of disrupting the function and structure of such systems. Overall this thesis aims to outline and evaluate the recent dramatic changes in multi-annual population cycles of many herbivores and the possible implications of such changes on the trophic dynamics and species conservation in the Fennoscandinavian tundra ecosystem. First I show that the recent collapse of multi-annual population cyclles are now a widespread phenomenon, extending several species and ecosystem barriers. Next I show, based on long time series of fox bounty data, that these recent changes have some historical analogies. Specifically, I show that the highly publicized patterns (e.g. geographic gradients, large scale synchrony) in Fennoscandian small rodent cycle have been buject to large spatio-temporal trensitions in their patterns, being highly non-stationary. I also demonstrate that collapse of cycles similar to the recent events, though on a smaller spatial extent, have occurred earlier and that these incidents seem to concur with shifts between cold and warm climatic periods. Then I demonstrate wich aspects of the recent changes in the dynamics of key prey species is likely to heavily affect the viability and existence of tundra predatirs strongly adapted to the pulsed flow of resources provided bycyclically fluctuating prey populations. Furthermore, the effect of recent and future projections of climate change may facilitate the establishment of novel predator species, which may act as dominant competitors for native species for habitat and prey. I here show that increased competition with red fox may be detrimental to arctic fox viability, especially if subsidies (e.g. reindeer carcasses) are available to the dominant competitor. Finally, I show that attempts to conserve native predators, such as the arctic fox, should take into account the factors that govern their demography and thus population dynamics. I show thet the effect of management action is highly dependent onthe phase of the demographic cycle of arctic fox. This means that management intervantion should be continous, but most focused to moments in time where the effect is expected to be most pronounced.
Description: Papers number 1,2 and 3 of the thesis are not available in Munin due to publishers' restrictions.
1.Rolf A. Ims, John-André Henden, Siw T. Killengreen.: "Collapsing population cycles." Trends in Ecology & Evolution; 23(2): 79-86 (Science Direct). Available at
2.John-André Henden, Rolf A. Ims, Nigel G. Yoccoz.: "Nonstationary spatio-temporal small rodent dynamics: evidence from long-term Norwegian fox bounty data." Journal of Animal Ecology; 78(3): 636-645 (Wiley). Available at
3.John-André Henden , Bård-Jørgen Bårdsen, Nigel G. Yoccoz, Rolf A. Ims.: " Impacts of differential prey dynamics on the potential recovery of endangered arctic fox populations." Journal of Applied Ecology Journal of Applied Ecology; 45(4): 1086-1093 (Wiley). Available at
Publisher: Universitetet i Tromsø; University of Tromsø

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Files Size Format View Description
thesis.pdf 5.460Mb PDF View/Open thesis introduction with discussion and conclusions
paper-4.pdf 609.9Kb PDF View/Open Henden, John-André; Ims, Rolf Anker; Yoccoz, Nigel Gilles; Hellström, Peter; Angerbjörn, Anders. 'Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundra', accepted manuscript. Published version: Oikos (2010), 119(1) 27-34 doi: 10.1111/j.1600-0706.2009.17604.x
paper-5.pdf 317.3Kb PDF View/Open Henden, John-André; Yoccoz, Nigel Gilles; Ims, Rolf Anker; Bårdsen, Bård-Jørgen; Angerbjörn, Anders. 'Phase-dependent effect of conservation efforts in cyclically fluctuating populations of arctic fox (Vulpes lagopus)', accepted manuscript. Published version: Biological Conservation (2009), 142(11) 2586-2592 doi: 10.1016/j.biocon.2009.06.005

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