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- Ekerholm, Per, 1959-
(författare)
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Population dynamics of tundra-living grey-sided voles
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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- Ekerholm, Per, et al.
(författare)
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The impact of short-term predator removal on vole dynamics in a arctic-alpine landscape
- 2004
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Ingår i: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; 106:3, s. 457-468
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Tidskriftsartikel (refereegranskat)abstract
- During 1991–95, mammalian predators (weasel, Mustela nivalis, stoat, M. erminea, mink, M. vison, and red fox, Vulpes vulpes) were excluded in late summers from a 2 ha piece of a north Norwegian mountain slope. The exclosure extended from an outpost of luxuriant sub-arctic birch forest to a typical arctic–alpine habitat complex, including productive willow scrublands, tundra heaths, dry ridges and snow-beds. The exclosure thus encompassed the entire range of habitat conditions encountered in a typical north Fennoscandian mountain and tundra landscapes. During 1991–95, the exclosure was predator-proof from late July to late September. In wintertime and in early summer, the exclosure was accessible to mammalian predators. Vole dynamics in the short-term exclosure were compared to dynamics in five reference areas with similar habitat conditions.In 1991, when vole densities were rising in the area, neither collective vole densities nor densities of individual vole species differed significantly between the exclosure and the replicated controls. Spring densities of voles were never significantly different between the exclosure and the controls. With respect to autumnal densities of voles, however, the exclosure was a statistical outlier in the peak year 1992 and throughout the gradual decline phase of 1993–95. In the peak year, the difference in collective vole densities was modest (30%), but increased to two-fold during the first two decline years and was almost four-fold in the crash year of 1995. The strongest response was displayed by field voles (Microtus agrestis), hypothesized to be the pivotal prey species of weasels, especially by females and young individuals, i.e. by the functional categories especially sensitive to mammalian predation. These results are consistent with the hypothesis that predation plays a pivotal role for the regulation of herbivorous mammals in relatively productive arctic–alpine habitats.
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- Ellman Kareld, Louise, et al.
(författare)
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Länsprogram Kronobergs län : Regional miljöövervakning 2015-2020
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- SammanfattningLänsprogrammet för Regional miljöövervakning, 2015-2020 för Kronobergs län, omfattar åtta programområden: Luft, Skog, Jordbruk, Våtmarker, Landskap, Sötvatten, Miljögiftssamordning och Hälsorelaterad miljöövervakning. Övervakning planeras inom 24 delprogram, fördelade på åtta programområden. Inom två delprogram sker övervakning först nästa programperiod.Fem ingående delprogram är nationella, de genomförs över hela landet. I länet har övervakning genom Gemensamma delprogram prioriterats.19 delprogram är sådana och genomförs i samarbete med andra län. De är markerade med en asterisk (*) i anslutning till rubriken. Inga gemensamma delprogram leds dock från länet under den kommande programperioden. De gemensamma delprogrammen möjliggörs övervakning inom samtliga åtta programområden.I länsprogrammet redovisas, oberoende av finansiär, den övervakning i Kronobergs län som ska bedrivas kontinuerligt under programperioden. Den totala kostnaden för hela programmet är svår att beräkna. Naturvårdsverket lämnar bidrag med 852 000 kronor årligen, men det finns även andra medel till andra särskilt riktade medel för exempelvis kalkeffektuppföljningen inom programområde Sötvatten som Hav- och vattenmyndigheten fördelar. Inom programområde Sötvatten finansieras recipientkontrollen helt av Vattenvårdsförbunden m.fl., och råvattenkontrollen delvis av länets kommuner. Övervakning inom programområde Luft sker genom Kronobergs läns luftvårdsförbund. Övervakningen av luftföroreningar i tätorter finansieras till största delen av kommunerna inom ett så kallat samverkansområde för kontroll av luftkvalitet. Inom programområde Hälsa och miljögifter finns en god samverkan med Landstinget Kronoberg och länets kommuner.Länsprogrammet innebär att data samlas in för att ge underlag för uppföljning av preciseringar och regionala miljömål till Miljökvalitetsmålen Frisk luft, Bara naturlig försurning, Giftfri miljö, Ingen övergödning, Levande sjöar och vattendrag, Grundvatten av god kvalitet, Levande skogar, Ett rikt odlingslandskap, God bebyggd miljö och Ett rikt växt- och djurliv.
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- Oksanen, Lauri, et al.
(författare)
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Islands as tests of the green world hypothesis.
- 2010
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Ingår i: Trophic Cascades – Predators, Prey, and the changing dynamics of Nature. - Washihgton DC : Island Press. - 9781597264860 ; , s. 163-178, s. 163-178
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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- Turchin, Peter, et al.
(författare)
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Are lemmings prey or predators?
- 2000
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Ingår i: Nature. - 0028-0836. ; 405, s. 562-565
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Tidskriftsartikel (refereegranskat)
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