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Visar resultat 1 - 5 av 15 avhandlingar som matchar ovanstående sökkriterier.

1. 1. Predator responses to non-stationary rodent cycles

   Författare :Peter Hellström; Anders Angerbjörn; Xavier Lambin; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Buteo lagopus; Vulpes lagopus; Lemmus; Myodes; population cycles; predation; numerical response; functional response; arctic; lemmings; voles; fox; monitoring; raptors; zoologisk ekologi; Animal Ecology;

   Sammanfattning : 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. LÄS MER

3. 2. Top-down and bottom-up effects in a Fennoscandian tundra community

   Författare :Doris Grellmann; Lars Ericson; Lauri Oksanen; Richard Inouye; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; consumer-resource interactions; exclosures; food web dynamics; grey-sided voles; lemmings; NPK-fertilization; plant defences; reindeer; soil microbes; vertebrate grazing;

   Sammanfattning : The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath.I conducted a large-scale fertilization experiment and studied the impact of grazers using exclosures. LÄS MER

4. 3. Herbivory and plant community structure in a subarctic altitudinal gradient

   Författare :Jon Moen; Nancy Huntly; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; arctic and alpine vegetation; competition; exclosures; lemmings; plant defences; plant-plant interactions; Ranunculus glacialis; snow-bed; structuring factors; tall herb meadow; vertebrate grazing; voles;

   Sammanfattning : The object of this thesis was to study plant community structure, especially in relation to vertebrate herbivory, in an altitudinal gradient in the Fennoscandian mountain chain.A sowing experiment in a high alpine Ranunculus glacialis population showed that seeds germinated better in cleared microsites than under established individuals. LÄS MER

5. 4. Predator-prey dynamics in small mammals along gradients of primary productivity

   Författare :Tarja Oksanen; Christian Otto; N. C. Stenseth; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; cycles; herbivory; lemmings; mustelids; predation; productivitly; spatial heterogeneity; taiga; trophic exploitation; tundra;

   Sammanfattning : .... LÄS MER

7. 5. Phylogeography and mitochondrial DNA diversity in arctic lemmings

   Författare :Vadim B. Fedorov; Uppsala universitet; []
   Nyckelord :MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Genetics; Genetik; Clinical genetics; Klinisk genetik; Genetics; genetik;

   Sammanfattning : The aim of this thesis is to evaluate the effects of Quaternary environmental fluctuations on the present patterns of mitochondrial DNA variation in the wood lemming, Myopus schisticolor, and the two genera of Arctic lemmings: collared lemmings, Dicrostonyx, and true lemmings, Lemmus.The phylogeographic pattern and the limited mtDNA diversity in the Scandinavian populations of the wood lemming reflect recent colonization by a limited number of founders during the Holocene boreal forest expansion. LÄS MER