| 1. |
- Henden, John-André, et al.
(författare)
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Strength of asymmetric competition between predators in food webs ruled by fluctuating prey : the case of foxes in tundra
- 2010
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 119:1, s. 27-34
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Norén, Karin, et al.
(författare)
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Arctic fox Vulpes lagopus population structure : circumpolar patterns and processes
- 2011
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 120:6, s. 873-885
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Tidskriftsartikel (refereegranskat)abstract
- Movement is a prominent process shaping genetic population structure. In many northern mammal species, population structure is formed by geographic distance, geographical barriers and various ecological factors that influence movement over the landscape. The Arctic fox Vulpes lagopus is a highly mobile, opportunistic carnivore of the Arctic that occurs in two main ecotypes with different ecological adaptations. We assembled microsatellite data in 7 loci for 1834 Arctic foxes sampled across their entire distribution to describe the circumpolar population structure and test the impact of (1) geographic distance, (2) geographical barriers and (3) ecotype designation on the population structure. Both Structure and Geneland demonstrated distinctiveness of Iceland and Scandinavia whereas low differentiation was observed between North America-northern Greenland, Svalbard and Siberia. Genetic differentiation was significantly correlated to presence of sea ice on a global scale, but not to geographical distance or ecotype designation. However, among areas connected by sea ice, we recorded a pattern of isolation by distance. The maximum likelihood approach in Migrate suggested that connectivity across North America-northern Greenland and Svalbard was particularly high. Our results demonstrate the importance of sea ice for maintaining connectivity between Arctic fox populations and we therefore predict that climate change will increase genetic divergence among populations in the future.
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| 3. |
- Nyström, Veronica, et al.
(författare)
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Genetic consequences of a demographic bottleneck in the Scandinavian arctic fox
- 2006
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 114:1, s. 84-94
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Tidskriftsartikel (refereegranskat)abstract
- Demographic bottlenecks can result in a loss of genetic variation due to the bottleneck effect and subsequent genetic drift. The arctic fox population in Scandinavia went through a severe demographic bottleneck in the early 20th century, and is today classified as critically endangered. In this study, we investigated the pre-bottleneck genetic variation in Scandinavia and compared it to modern samples from Scandinavia and North Russia. Variation in the mtDNA control region and five microsatellite loci was examined through ancient DNA analysis on museum specimens. The microsatellite data from the museum specimens was further used to simulate the expected effect of the bottleneck. The arctic foxes in Scandinavia have lost approximately 25% of the microsatellite alleles and four out of seven mtDNA haplotypes. The results also suggest that the genetic differentiation between North Russia and Scandinavia has doubled over the last 100 years. However, the level of heterozygosity was significantly higher than expected from the simulations. This highlights both the advantage of using museum specimens and the importance of generating specific predictions in conservation genetics.
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| 4. |
- Angerbjörn, Anders
(författare)
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Gigantism in Island Populations of Wood Mice (Apodemus) in Europe
- 1986
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 47:1, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- Many rodents have large body sizes on islands, and there are many hypotheses that try to explain this observed pattern. Using body size data on Apodemus in Europe as an example, I try to evaluate the main hypotheses. These can be divided in four different categories. 1) Hypotheses assuming climatic differences between islands and mainland: no trend in body size on islands in the Mediterranean, in Britain or in the Baltic area is observed. 2) Hypotheses based on island size: no trend is observed in the data analysed. 3) Hypotheses based on distance to mainland: no general effect is found, although there is an effect in the British material. 4) Hypotheses based on faunistic differences: consistent relationships are found in all areas. A. sylvaticus shows larger body size when lacking competition from A. flavicollis or Clethrionomys glareolus or when predation is absent. A. flavicollis is larger when predators are lacking, and smaller when no competitors are present. This is in agreement with character displacement theory
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| 5. |
- Elmhagen, B.odil, et al.
(författare)
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The applicability of metapopulation theory to large mammals
- 2001
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 94, s. 89-100
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Tidskriftsartikel (refereegranskat)abstract
- Metapopulation theory has become a common framework in conservation biology and it is sometimes suggested that a metapopulation approach should be used for management of large mammals. However. it has also been suggested that metapopulation theory would not be applicable to species with long generations compared to those with short ones. In this paper, we review how and on what empirical ground metapopulation terminology liar, been applied to insects, small mammals and large mammals, The review showed that the metapopulation term sometimes was used for population networks which only fulfilled the broadest possible definition of a metapopulation, i.e. they were subpopulations connected by migrating individuals. We argue that the metapopulation concept should be reserved for networks that also show some kind of metapopulation dynamics. Otherwise it applies to almost all populations and loses its substance. We found much empirical support for metapopulation dynamics in both insects and small mammals, but not in large mammals. A me possible reason is the methods used to confirm the existence of metapopulation dynamics, For insects and small mammals, the common approach is to study population turnover through patch occupancy data. Such data is difficult to obtain for large mammals, since longer temporal scales need to be covered to record extinctions and colonizations. Still, many populations of large mammals are exposed to habitat fragmentation and the resulting subpopulations sometimes have high risks of extinction. If there is migration between the subpopulations, the metapopulation framework could provide valuable information on their population dynamics. We suggest that a metapopulation approach can be interesting for populations of large mammals. when there are discrete breeding subpopulations and when these subpopulations have different growth rates and demographic fates. Thus, a comparison of the subpopulations' demographic fates, rather than subpopulation turnover, can be a feasible alternative for studies of metapopulation dynamics in large mammals.
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| 6. |
- Meyer, Nicolas, et al.
(författare)
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Nest attentiveness drives nest predation in arctic sandpipers
- 2020
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 129:10, s. 1481-1492
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Tidskriftsartikel (refereegranskat)abstract
- Most birds incubate their eggs to allow embryo development. This behaviour limits the ability of adults to perform other activities. Hence, incubating adults trade off incubation and nest protection with foraging to meet their own needs. Parents can either cooperate to sustain this tradeoff or incubate alone. The main cause of reproductive failure at this reproductive stage is predation and adults reduce this risk by keeping the nest location secret. Arctic sandpipers are interesting biological models to investigate parental care evolution as they may use several parental care strategies. The three main incubation strategies include both parents sharing incubation duties ('biparental'), one parent incubating alone ('uniparental'), or a flexible strategy with both uniparental and biparental incubation within a population ('mixed'). By monitoring the incubation behaviour in 714 nests of seven sandpiper species across 12 arctic sites, we studied the relationship between incubation strategy and nest predation. First, we described how the frequency of incubation recesses (NR), their mean duration (MDR), and the daily total duration of recesses (TDR) vary among strategies. Then, we examined how the relationship between the daily predation rate and these components of incubation behaviour varies across strategies using two complementary survival analysis. For uniparental and biparental species, the daily predation rate increased with the daily total duration of recesses and with the mean duration of recesses. In contrast, daily predation rate increased with the daily number of recesses for biparental species only. These patterns may be attributed to two independent mechanisms: cryptic incubating adults are more difficult to locate than unattended nests and adults departing the nest or feeding close to the nest can draw predators' attention. Our results demonstrate that incubation behaviour as mediated by incubation strategy has important consequences for sandpipers' reproductive success.
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| 7. |
- Tannerfeldt, Magnus, et al.
(författare)
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Fluctuating resources and the evolution of litter size in the arctic fox
- 1998
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Ingår i: Oikos. - : Blackwell. - 0030-1299 .- 1600-0706. ; 83:3, s. 545-559
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Tidskriftsartikel (refereegranskat)abstract
- Fluctuations in essential resources cause a strong selection pressure on the ability to adjust parental investment accordingly. In the dog family, Canidae, variance in female prebirth investment is adjusted by litter size. The arctic fox, Alopex lagopus, is a small canid living on the northern tundras of the world. It has the largest known litter size in the order Carnivora. up to 18 young, and litter size is highly variable. We have analysed data From arctic fox populations throughout the species circumpolar range. In some areas, arctic foxes feed on strongly fluctuating populations of small rodents. In contrast, they have more stable food resources at bird cliffs and along coast lines. Food availability determines arctic fos litter and population sizes. A comparison between fluctuating and stable arctic fox populations showed that fluctuations are associated with large litter sizes. There were significant differences in litter size means, maxima and variances, as well as in placental scar count means. We have discussed five hypotheses on the determination of variation in litter size: one energetic, one genetic (based on density variation), one diet-determined, one based on reproductive allocation and one based on differences in reaction norms. Our findings suggest that litter size in the arctic fox is determined by the combined effect of immediate resource levels and the degree of resource predictability. We describe reaction norms that suggest how litter sizes result from adaptive plasticity within each of two genetic strategies where, according to the jackpot hypothesis, populations with unpredictable food resources generally have larger litter sizes. Within each genetic strategy, or reaction norm, litter sizes are adjusted through a number of plastic trails. These traits are influenced by nutritional limitations and include reduced ovulation rates, prenatal losses, and litter size reduction during the lactation period.
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