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Mechanisms of apparent competition in seasonal environments: an example with vole herbivory
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
1997 In: Oikos, ISSN 0030-1299, Vol. 80, 276-288 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
1997. Vol. 80, 276-288 p.
URN: urn:nbn:se:umu:diva-3522OAI: diva2:142261
Available from: 2004-01-30 Created: 2004-01-30Bibliographically approved
In thesis
1. Population dynamics of tundra-living grey-sided voles
Open this publication in new window or tab >>Population dynamics of tundra-living grey-sided voles
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the dynamics of tundra living voles with emphasis on the most common one, the grey-sided vole (Clethrionomys rufocanus). The tundra area chosen for the study was Finnmarksvidda, a vast flatland in northernmost Norway. All small mammal herbivores in the area showed dramatic fluctuations, and field experiment were conducted in order to elucidate these density fluctuations. The specific subjects addressed included: 1/ Temporal and spatial appearance of density fluctuations of voles and lemmings in the area, 2/ The generality of the density patterns observed, 3/ The impact of predation by vole predators during summertime, 4/ The impact of grey-sided vole grazing on food plants of different preference in a predator free environment, in the presence and absence of extra food, and 5/ The impact of food availability on density and demography of grey-sided voles in a predator free environment.

The results achieved showed that voles in the slope and lowland had cyclic density fluctuations with 5 years duration. The cycles consisted of four phases: an increase phase, a peak phase, a decline phase and a crash phase. In the unproductive lowland and on the moderately productive slope, small pockets of productive habitats seemed to work as “triggers” for the cycles. The lemming fluctuations in the upper plateau (separated from the slope by a steep zone of boulders) differed markedly from the vole patterns in the lowland.

Only two lemming peaks were recorded in twenty years. Both peaks had very short increase phases, a knife-sharppeak phase and no decline phase before the crash. A comparison between our results and lemming and vole populations from two other areas in Fennoscandia revealed the same difference in fluctuation pattern between lemmings and voles as seen in our area. This results suggests that lemmings in barren tundra highlands and voles in slightly more productive tundra lowlands are regulated by different mechanisms.

The exclusion of vole predators from vole populations during summertime led to increase in overall vole density. Densities of the clumsy field vole (Microtus agrestis) and juveniles of all species showed the strongest positive effects of the exclusion.

An experiment analysing the effects of food availability was conducted in islands in a large lake where grey-sided voles were introduced to predator free islands . Supplemental food was given to the voles in two unproductive, and two productive islands. Two unproductive and two productive islands were used as reference islands. The density of voles and the vole weight were higher in both the islands with supplemental food and those with high natural productivity. Increased vole density did not significantly increase grazing damage to plants. The cyclic density pattern of the voles in the nearby mainland (that harboured resident vole specialist predators as stoat and weasel) showed little resemblance to the seasonal fluctuations found in the islands (devoid of resident vole specialist predators). This result suggested that predation by stoat and weasel on grey-sided vole populations may cause the cyclic vole fluctuations seen in the area.

38 p.
Ecology, Population dynamics, Tundra, Grey-sided vole, Cycles, Vole specialist predators, Ekologi
National Category
Research subject
Animal Ecology
urn:nbn:se:umu:diva-187 (URN)91-7305-300-7 (ISBN)
Public defence
2003-06-16, Stora hörsalen, KBC, Umeå, 08:15
Available from: 2004-01-30 Created: 2004-01-30Bibliographically approved

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