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Predator-prey interactions of raptors in an arctic environment
Stockholm University, Faculty of Science, Department of Zoology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the predator-prey interactions of three raptor species in a Swedish arctic community: the gyrfalcon (Falco rusticolus), the rough-legged buzzard (Buteo lagopus) and the golden eagle (Aquila chrysaetos).

The gyrfalcon behaved like a highly specialised ptarmigan (Lagopus spp.) predator. Gyrfalcon’s functional response to ptarmigan was close to density independent, and ptarmigan remained the dominating prey even in areas with the lowest ptarmigan density. The gyrfalcon did not respond functionally to microtine rodents (i.e. lemmings and voles) and it was clear that the gyrfalcon did not use microtines as an alternative prey category to ptarmigan. As the gyrfalcons did not switch to any alternative prey when ptarmigan was scarce, their reproductive success seemed to be directly dependent on the amount of ptarmigan available in the breeding territories. Of the two ptarmigan species in the study area, rock ptarmigan (L. mutus) dominated gyrfalcon’s diet. Locally, the proportion of rock ptarmigan in gyrfalcons’ diets showed a positive relationship to the expected availability of rock ptarmigan in the breeding territories, indicating a density dependent utilisation.

The rough-legged buzzard behaved like a highly specialised microtine rodent predator and Norwegian lemming (Lemmus lemmus) was its preferred microtine species. The buzzards showed a type 2 functional response to lemmings. Surprisingly though, they also had a type 3 functional response to grey-sided voles (Clethrionomus rufocanus). We present an optimal diet model where a central place forager, during good food conditions, benefits from partial prey preference, which renders separate functional responses to each prey category. We discuss how the double functional responses of the buzzard affect the population dynamics of sympatric vole species, on both temporal and spatial scales.

The golden eagle behaved like a generalist predator, and it preyed on all major prey categories in the study area: microtines, ptarmigan, mountain hare, (Lepus timidus) and reindeer (Rangifer tarandus). It seemed to respond functionally to microtine rodent fluctuations with an increased consumption of lemmings during a peak year in the microtine rodent cycle. The golden eagle showed a numerical response to its main prey, the ptarmigan.

Ptarmigan, microtine rodents and hares seemed to have synchronized population fluctuations in the study area. Such synchronized population fluctuations are believed to be generated by predation. Although the three raptors are the main predators of their community, their predation patterns fail to explain the observed prey population dynamics in the study area.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen , 2004. , 32 p.
Keyword [en]
Ecology of raptors
National Category
Ecology
Identifiers
URN: urn:nbn:se:su:diva-259ISBN: 91-7265-950-5 (print)OAI: oai:DiVA.org:su-259DiVA: diva2:191641
Public defence
2004-10-22, sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2011-11-07Bibliographically approved
List of papers
1. Gyr falcons, ptarmigan and microtine rodents in Northern Sweden
Open this publication in new window or tab >>Gyr falcons, ptarmigan and microtine rodents in Northern Sweden
2005 (English)In: Ibis, ISSN 0019-1019, E-ISSN 1474-919X, Vol. 147, no 3, 587-597 p.Article in journal (Refereed) Published
Abstract [en]

A Gyr Falcon Falco rusticolus population in Northern Sweden (66°N, 17°E) was monitored from 1996 to 2002 in relation to its predator–prey interactions with its main and alternative prey species. Ptarmigan species Lagopus spp., and especially Rock Ptarmigan L. mutus, were the Gyr Falcons’ most important prey and constituted more than 90% of the prey biomass. A 21-fold difference in ptarmigan abundance was found across Falcon breeding territories. However, this great variation in prey availability corresponded to only about a 10% shift in Gyr Falcon diet across territories, suggesting that the Falcons were reluctant or unable to compensate for declining ptarmigan availability by using alternative prey categories. Gyr Falcons did not respond functionally to microtine rodent abundance. Their diets were unaffected by a peak in the microtine rodent population cycle when Norwegian Lemmings Lemmus lemmus occurred in high numbers in the study area. Gyr Falcons responded numerically to their prey in two ways. First, there was a reproductive response with a significant relationship between the number of chicks fledged and the number of ptarmigan in the breeding territories. Secondly, although the Gyr Falcons did not utilize microtines as prey, there was a relationship between the microtine rodent abundance and the number of pairs that attempted to breed each year. This could be a result of an indirect community interaction, assuming that other predators switched from ptarmigan to microtines as prey, which could have had a positive effect on the breeding performance of the Gyr Falcons. The Gyr Falcons acted as true specialist predators, and their narrow food niche probably reflected a general lack of suitable alternative prey in the study area.

National Category
Zoology
Identifiers
urn:nbn:se:su:diva-23376 (URN)10.1111/j.1474-919x.2005.00436.x (DOI)
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2017-12-13Bibliographically approved
2. Effect of local prey availability on gyrfalcon diet: DNA analysis on ptarmigan remains at nest sites
Open this publication in new window or tab >>Effect of local prey availability on gyrfalcon diet: DNA analysis on ptarmigan remains at nest sites
Show others...
2006 (English)In: Journal of Zoology, ISSN 0952-8369, E-ISSN 1469-7998, Vol. 269, no 1, 57-64 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate how the diet of gyrfalcon Falco rusticolus in northern Sweden was affected by the relative availability of its two main prey species: rock ptarmigan Lagopus mutus and willow ptarmigan Lagopus lagopus. In order to do so, we needed a method to estimate the gyrfalcon's diet proportions of rock and willow ptarmigan from prey remains that we collected from nest sites in separate breeding territories. We also needed a method to calculate the availability of the two prey species in the same breeding territories that the prey remains originated from. We could then compare the diet proportions with prey availability and investigate if the gyrfalcons utilized the two species strictly in relation to their densities, or if they showed a preference for any of the prey species. Morphometric identification to species level from ptarmigan remains was not possible. Therefore, we developed a PCR-based process of DNA analysis, which could be applied on any ptarmigan bone or bone remains. This method allowed us to establish the ratio of rock and willow ptarmigan in gyrfalcon diets that originated from single gyrfalcon breeding occasions. The relative availability of the two ptarmigan species in gyrfalcon breeding territories was calculated with a GIS model that incorporated observations on ptarmigan habitat preferences. The DNA identification was performed on 176 ptarmigan bones from 13 different breeding occasions occurring in five different territories. The results indicated that the two ptarmigan species comprised at least 93% of the average gyrfalcon diet, and that rock ptarmigan was the most common prey during all 13 breeding occasions. There was a positive relationship between the relative amount of rock ptarmigan in the diet and the proportion of rock ptarmigan habitat in the territories; hence, the gyrfalcons ptarmigan utilization seemed to be density dependent. However, rock ptarmigan was found to be overrepresented in the diet, which may reflect a preference for rock ptarmigan over willow ptarmigan. The conservation implications of these findings in relation to ptarmigan hunting are discussed.

Keyword
PCR, molecular approach, diet, predator–prey, conservation
National Category
Zoology
Identifiers
urn:nbn:se:su:diva-23377 (URN)10.1111/j.1469-7998.2006.00050.x (DOI)
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2017-12-13Bibliographically approved
3. Functional responses generated by spatial variation in prey density: buzzards versus rodents
Open this publication in new window or tab >>Functional responses generated by spatial variation in prey density: buzzards versus rodents
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23378 (URN)
Note
Part of urn:nbn:se:su:diva-259Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2010-01-13Bibliographically approved
4. Golden Eagles on the Swedish mountain tundra - diet and breeding success in relation to prey fluctuations
Open this publication in new window or tab >>Golden Eagles on the Swedish mountain tundra - diet and breeding success in relation to prey fluctuations
Show others...
2006 (English)In: Ornis Fennica, ISSN 0030-5685, Vol. 83, no 4, 145-152 p.Article in journal (Refereed) Published
Abstract [en]

We studied the diet and the relationship between prey density fluctuations and breeding success of a Golden Eagle (Aquila chrysaetos) population on the mountain tundra region of northern Sweden. We used a new PCR based method to analyse the DNA in bone fragments from Golden Eagle prey remains. This allowed us to accurately identify the Ptarmigan species that the bone fragments originated from, and hence, establish the proportions of Ptarmigan species in the eagle's diet. We could conclude that Ptarmigan species (Lagopus spp.) are the most important prey category for this Golden Eagle population (63% of all identified prey), and that Willow Ptarmigan (L. lagopus) occurred more frequently in the diet than Rock Ptarmigan (L. mutus) did (Willow Ptarmigan 38%, Rock Ptarmigan 25%). Other important prey included reindeer (Rang fer tarandus), mountain hare (Lepus timidus) and microtine rodents. The Golden Eagles managed to maintain a relatively broad food niche, despite an environment with low prey diversity. Microtine rodents, hare and Ptarmigan populations showed similar population fluctuations in the study area. The breeding success of the Golden Eagles showed a strong relationship to the yearly density index of the most important prey category, the Ptarmigan species.

National Category
Zoology
Research subject
Zoology
Identifiers
urn:nbn:se:su:diva-29707 (URN)0030-5685 (ISBN)
Available from: 2009-09-10 Created: 2009-09-10 Last updated: 2017-12-13Bibliographically approved

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