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Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundra
University of Tromsø, Norway.
University of Tromsø, Norway.
University of Tromsø, Norway.
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-5124-2534
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2010 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 1, 27-34 p.Article in journal (Refereed) Published
Abstract [en]

In food webs heavily influenced by multi-annual population fluctuations of key herbivores, predator species may differ in their functional and numerical responses as well as their competitive ability. Focusing on red and arctic fox in tundra with cyclic populations of rodents as key prey, we develop a model to predict how population dynamics of a dominant and versatile predator (red fox) impacted long-term growth rate of a subdominant and less versatile predator (arctic fox). We compare three realistic scenarios of red fox performance: (1) a numerical response scenario where red fox acted as a resident rodent specialist exhibiting population cycles lagging one year after the rodent cycle, (2) an aggregative response scenario where red fox shifted between tundra and a nearby ecosystem (i.e. boreal forest) so as to track rodent peaks in tundra without delay, and (3) a constant subsidy scenario in which the red fox population was stabilized at the same mean density as in the other two scenarios. For all three scenarios it is assumed that the arctic fox responded numerically as a rodent specialist and that the mechanisms of competition is of a interference type for space, in which the arctic fox is excluded from the most resource rich patches in tundra. Arctic fox is impacted most by the constant subsidy scenario and least by the numerical response scenario. The differential effects of the scenarios stemmed from cyclic phase-dependent sensitivity to competition mediated by changes in temporal mean and variance of available prey to the subdominant predator. A general implication from our result is that external resource subsidies (prey or habitats), monopolized by the dominant competitor, can significantly reduce the likelihood for co-existence within the predator guild. In terms of conservation of vulnerable arctic fox populations this means that the likelihood of extinction increases with increasing amount of subsidies (e.g. carcasses of large herbivores or marine resources) in tundra and nearby forest areas, since it will act to both increase and stabilize populations of red fox.

Place, publisher, year, edition, pages
2010. Vol. 119, no 1, 27-34 p.
National Category
Biological Sciences
URN: urn:nbn:se:su:diva-32481DOI: 10.1111/j.1600-0706.2009.17604.xISI: 000273069000003OAI: diva2:280637
Available from: 2009-12-21 Created: 2009-12-10 Last updated: 2015-09-17Bibliographically approved
In thesis
1. Predator responses to non-stationary rodent cycles
Open this publication in new window or tab >>Predator responses to non-stationary rodent cycles
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Regular fluctuations in population size, cycles, are common in small mammals and have important effects on predator populations and life histories. In this thesis, I identify long-term patterns and processes in two specialist predators, the arctic fox Vulpes lagopus and the rough-legged buzzard Buteo lagopus, in relation to their prey (lemmings and voles) and in the case of the arctic fox also to a dominant competitor, the red fox Vulpes vulpes. The results demonstrate that the specialist predators as expected were limited by food supply, which was revealed by combining long-term monitoring with a pseudo-experimental approach. But dampening of cycles has led to long-term declines in the predator populations. Cycles in red and arctic foxes disappeared in the 1970s and 1980s. A return to cyclic dynamics was found locally in the red fox in the boreal zone, but monitoring in the mountain region identified a widespread return of cycles in both lemmings and voles in the early 2000s. This increase in natural food was sufficient to halt the decline in the arctic fox population, but a large-scale field experiment revealed that only supplementary fed subpopulations increased in size. Competition with the red fox further had a negative impact on the arctic fox population. A theoretical model suggested that this asymmetric competition is context dependent and most severe if red fox numbers are independent of rodent density due to access to alternative food. The number of breeding rough-legged buzzards was determined primarily by rodent abundance, but has been nearly halved since the 1970s and was decoupled from rodents in the most recent years. Reproductive output is currently also lower due to smaller clutch sizes. The functional responses of the rough-legged buzzard were complex and differed between lemmings and voles. Rodent cycles are clearly essential for maintaining biodiversity, but spatiotemporal patterns and effects on ecological communities are increasingly variable.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2014. 32 p.
Buteo lagopus, Vulpes lagopus, Lemmus, Myodes, population cycles, predation, numerical response, functional response, arctic, lemmings, voles, fox, monitoring, raptors
National Category
Research subject
Animal Ecology
urn:nbn:se:su:diva-102728 (URN)978-91-7447-922-5 (ISBN)
Public defence
2014-05-28, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)

At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2014-05-06 Created: 2014-04-17 Last updated: 2014-10-28Bibliographically approved

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