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Spatial and temporal population dynamics in the mountain tundra – mesopredator and prey
Stockholm University, Faculty of Science, Department of Zoology. (Svenska fjällrävsprojektet)ORCID iD: 0000-0002-9207-5709
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is well known that competition, predation and fluctuating food resources can have strong effect on individual fitness and population dynamics. The complexity of natural systems can make it complicate to disentangle those processes, but environments with relatively simple food webs, and strong cyclic population dynamics offer contrasting conditions resembling experimental treatments. This thesis concerns the spatial and temporal implications of fluctuations in small rodent abundance on two trophic levels in a highly cyclic ecosystem, the Scandinavian mountain tundra. The first two chapters focus on plant biomass and spatiotemporal distribution in the Norwegian lemming (Lemmus lemmus), while the three last papers focus on the direct and indirect effects of small rodent fluctuations and territory quality on reproductive success, juvenile survival and group living in a lemming specialist mesopredator, the arctic fox (Vulpes lagopus). By developing, validating and applying a novel application of aerial photos for remote sensing of plant biomass (Chapter I), we found that food availability predicted lemming distribution during population peaks, but that they were more habitat specific during increase years when intraspecific competition was lower (Chapter II). Arctic fox reproduction is tightly connected to small rodent abundance but the effects of geographical variation in food availability is less well known. We used 17 years of population surveys of an arctic fox subpopulation in mid Sweden (Helagsfjällen) to investigate potential effects. During small rodent increase years, we found that arctic fox litter sizes were smaller in territories of intermediate plant productivity, compared to both more and less productive territories (Chapter III). This could be an effect of limited food availability together with increased presence of red foxes (Vulpes vulpes), a stronger and potentially lethal competitor. However, when small rodents peaked, and competition would be expected to decrease, we saw no effect of territory productivity. Based on a smaller data set concerning juvenile summer survival, we found that the mortality rate among juveniles born by first time breeding arctic fox females were more sensitive to low small rodent prey abundance (Chapter IV). We explain it with an increased predation pressure from top-predators that switch from small rodents to alternative prey when small rodents decline, as suggested by an observed positive effect on juvenile survival by adult presence on den sites. Arctic foxes are socially flexible, and several adults can share a den with the resident pair, potentially increasing juvenile survival and help in territorial defence. Returning to the 17-year data set, we tested the Resource Dispersion Hypothesis predicting that increased resource availability should increase group size (Chapter V). We found support for this prediction as group living increased during the small rodent peak phase. However, it remained unexpectedly high during the decrease phase, when resources are scarce. This could however be related to increased predation pressure, and an increasing benefit of group living.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2019. , p. 17
Keywords [en]
population dynamics, cyclic, mountain tundra, arctic fox, Norwegian lemming, small rodents, mesopredator, predation, survival, reproduction
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-162539ISBN: 978-91-7797-540-3 (print)ISBN: 978-91-7797-541-0 (electronic)OAI: oai:DiVA.org:su-162539DiVA, id: diva2:1267147
Public defence
2019-01-25, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript. Paper 5: Manuscript.

Available from: 2018-12-19 Created: 2018-11-30 Last updated: 2019-02-04Bibliographically approved
List of papers
1. An innovative use of orthophotos - possibilities to assess plant productivity from colour infrared aerial orthophotos
Open this publication in new window or tab >>An innovative use of orthophotos - possibilities to assess plant productivity from colour infrared aerial orthophotos
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2019 (English)In: Remote Sensing in Ecology and Conservation, ISSN 0034-429X, E-ISSN 2056-3485Article in journal (Refereed) Published
Abstract [en]

Studies of ecological processes should focus on a relevant spatial scale, as crude spatial resolution will fail to detect small scale variation which is of potentially critical importance. Remote sensing methods based on multispectral satellite images are used to assess primary productivity and aerial photos to map vegetation structure. Both methods are based on the principle that photosynthetically active vegetation has a characteristic spectral signature. Yet they are applied differently due to technical differences. Satellite images are suitable for calculations of vegetation indices, for example Normalized Difference Vegetation Index (NDVI). Colour infrared aerial photography was developed for visual interpretation and never regarded for calculation of indices since the spectrum recorded and post processing differ from satellite images. With digital cameras and improved techniques for generating colour infrared orthophotos, the implications of these differences are uncertain and should be explored. We tested if plant productivity can be assessed using colour infrared aerial orthophotos (0.5 m resolution) by applying the standard NDVI equation. With 112 vegetation samples as ground truth, we evaluated an index that we denote rel‐NDVIortho in two areas of the Fennoscandian mountain tundra. We compared the results with conventional SPOT5 satellite‐based NDVI (10 m resolution). rel‐NDVIortho was related to plant productivity (Northern area: P = <0.001, R2 = 0.73; Southern area: P = <0.001, R2 = 0.39), performed similar to SPOT5 satellite NDVI (Northern area: P = <0.001, R2 = 0.76; Southern area: P = <0.001, R2 = 0.40) and the two methods were highly correlated (cor = 0.95 and cor = 0.84). Despite different plant composition, the results were consistent between areas. Our results suggest that vegetation indices based on colour infrared aerial orthophotos can be a valuable tool in the remote sensing toolbox, offering a high‐spatial resolution proxy for plant productivity with less signal degradation due to atmospheric interference and clouds, compared to satellite images. Further research should aim to investigate if the method is applicable to other ecosystems.

National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-165773 (URN)10.1002/rse2.108 (DOI)
Projects
Fjällrävsprojektet
Funder
Interreg Sweden-Norway, 20200939
Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-08-19Bibliographically approved
2. Spatial distribution in Norwegian lemming Lemmus lemmus in relation to the phase of the cycle
Open this publication in new window or tab >>Spatial distribution in Norwegian lemming Lemmus lemmus in relation to the phase of the cycle
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2018 (English)In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 41, no 7, p. 1391-1403Article in journal (Refereed) Published
Abstract [en]

Competition between individuals of the same or different species affects spatial distribution of organisms at any given time. Consequently, a species geographical distribution is related to population dynamics through density-dependent processes. Small Arctic rodents are important prey species in many Arctic ecosystems. They commonly show large cyclic fluctuations in abundance offering a potential to investigate how landscape characteristics relates to density-dependent habitat selection. Based on long-term summer trapping data of the Norwegian lemming (Lemmus lemmus) in the Scandinavian Mountain tundra, we applied species distribution modeling to test if the effect of environmental variables on lemming distribution changed in relation to the lemming cycle. Lemmings were less habitat specific during the peak phase, as their distribution was only related to primary productivity. During the increase phase, however, lemming distribution was, in addition, associated with landscape characteristics such as hilly terrain and slopes that are less likely to get flooded. Lemming habitat use varied during the cycle, suggesting density-dependent changes in habitat selection that could be explained by intraspecific competition. We believe that the distribution patterns observed during the increase phase show a stronger ecological signal for habitat preference and that the less specific habitat use during the peak phase is a result of lemmings grazing themselves out of the best habitat as the population grows. Future research on lemming winter distribution would make it possible to investigate the year around strategies of habitat selection in lemmings and a better understanding of a fundamental actor in many Arctic ecosystems.

Keywords
Small rodents, Density-dependent, Competition, Habitat, Primary productivity
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-153974 (URN)10.1007/s00300-018-2293-6 (DOI)000437102400007 ()
Projects
Svenska fjällrävsprojektet
Funder
Interreg Sweden-Norway
Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2018-12-04Bibliographically approved
3. Limitations of a weaker competitor – Implications of territory quality on the reproductive output of a tundra specialist
Open this publication in new window or tab >>Limitations of a weaker competitor – Implications of territory quality on the reproductive output of a tundra specialist
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-162536 (URN)
Projects
Svenska fjällrävsprojektet
Available from: 2018-11-30 Created: 2018-11-30 Last updated: 2018-12-04Bibliographically approved
4. Indirect effects of prey fluctuation on survival of juvenile arctic fox (Vulpes lagopus): a matter of maternal experience and litter attendance
Open this publication in new window or tab >>Indirect effects of prey fluctuation on survival of juvenile arctic fox (Vulpes lagopus): a matter of maternal experience and litter attendance
2017 (English)In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 95, p. 239-246Article in journal (Refereed) Published
Abstract [en]

Reproductive experience affects juvenile survival in a wide range of species with possible links to differences in foraging capacity and predation. Using supplementary feeding, we aimed to limit direct effect of prey abundance to investigate indirect effects of small-rodent availability and maternal experience on juvenile summer survival rates in an endangered population of arctic fox (Vulpes lagopus (L., 1758)). We used data spanning 7 years, included a complete small-rodent cycle, comprising 49 litters and 394 cubs. The effect of small-rodent abundance on juvenile survival depended on maternal breeding experience. Cubs born by first-time-breeding females had lower survival rate when small-rodent abundance was low compared with juveniles born to experienced mothers who remained unaffected. It was unlikely due to starvation, as physical condition was unrelated to survival. Instead, we favour the explanation that intraguild predation was an important cause of mortality. There was a negative relationship between survival and amount of time cubs were left unattended, suggesting that parental behaviour affected predation. We propose that a prey switch related to small-rodent abundance caused fluctuations in intraguild predation pressure and that inexperienced females were less able to cope with predation when small rodents were scarce.

Keywords
arctic fox, Vulpes lagopus, juvenile survival, small rodents, cyclic, maternal experience, behaviour, intraguild predation
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-140943 (URN)10.1139/cjz-2016-0103 (DOI)000399167300002 ()
Projects
Svenska fjällrävsprojektet
Available from: 2017-03-24 Created: 2017-03-24 Last updated: 2018-12-04Bibliographically approved
5. The resource dispersion hypothesis – a test with a cyclic mesopredator
Open this publication in new window or tab >>The resource dispersion hypothesis – a test with a cyclic mesopredator
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-162538 (URN)
Available from: 2018-11-30 Created: 2018-11-30 Last updated: 2018-12-04Bibliographically approved

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