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Predator responses to non-stationary rodent cycles
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-5124-2534
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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. The results demonstrate that the specialist predators as expected were limited by food supply, which was revealed by combining long-term monitoring with a pseudo-experimental approach. But dampening of cycles has led to long-term declines in the predator populations. Cycles in red and arctic foxes disappeared in the 1970s and 1980s. A return to cyclic dynamics was found locally in the red fox in the boreal zone, but monitoring in the mountain region identified a widespread return of cycles in both lemmings and voles in the early 2000s. This increase in natural food was sufficient to halt the decline in the arctic fox population, but a large-scale field experiment revealed that only supplementary fed subpopulations increased in size. Competition with the red fox further had a negative impact on the arctic fox population. A theoretical model suggested that this asymmetric competition is context dependent and most severe if red fox numbers are independent of rodent density due to access to alternative food. The number of breeding rough-legged buzzards was determined primarily by rodent abundance, but has been nearly halved since the 1970s and was decoupled from rodents in the most recent years. Reproductive output is currently also lower due to smaller clutch sizes. The functional responses of the rough-legged buzzard were complex and differed between lemmings and voles. Rodent cycles are clearly essential for maintaining biodiversity, but spatiotemporal patterns and effects on ecological communities are increasingly variable.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2014. , 32 p.
Keyword [en]
Buteo lagopus, Vulpes lagopus, Lemmus, Myodes, population cycles, predation, numerical response, functional response, arctic, lemmings, voles, fox, monitoring, raptors
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-102728ISBN: 978-91-7447-922-5 (print)OAI: oai:DiVA.org:su-102728DiVA: diva2:713717
Public defence
2014-05-28, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2014-05-06 Created: 2014-04-17 Last updated: 2014-10-28Bibliographically approved
List of papers
1. Changes in vole and lemming fluctuations in northern Sweden 1960-2008 revealed by fox dynamics
Open this publication in new window or tab >>Changes in vole and lemming fluctuations in northern Sweden 1960-2008 revealed by fox dynamics
2011 (English)In: Annales Zoologici Fennici, ISSN 0003-455X, E-ISSN 1797-2450, Vol. 48, no 3, 167-179 p.Article in journal (Refereed) Published
Abstract [en]

Cyclic dynamics with extensive spatial synchrony has long been regarded as characteristic of key herbivores at high latitudes. This contrasts to recent reports of fading cycles in arvicoline rodents in boreal and alpine Fennoscandia. We investigate the spatio-temporal dynamics of boreal red fox and alpine arctic fox in Sweden as a proxy for the dynamics of their main prey, voles and Norwegian lemming, respectively. We analyse data from five decades, 1960-2008, with wavelets and autocorrelation approaches. Cyclic dynamics were identified with at least one method in all populations (arctic fox n = 3, red fox n = 6). The dynamics were synchronous between populations, or coupled with a 1-yr lag, in 8 of 13 pairwise comparisons. Importantly though, the dynamics were heterogeneous in space and time. All analytical approaches identified fading cycles in the three arctic fox populations and two northern red fox populations. At least one method identified similar patterns in three southern red fox populations. Red fox dynamics were cyclic in the 1970s primarily, while arctic fox dynamics was cyclic until the late 1980s or early 1990s. When cyclic, 4-yr cycles dominated in arctic fox and northern red fox, whilst 3-4-yr cycles was found in southern red foxes. Significant cyclic regimes reappeared in the 1990s or 2000s in two red fox populations and one arctic fox population. Cycles and regionally coupled dynamics appeared associated in northern arctic and red foxes. This study supports accumulating evidence which suggests that cyclic and synchronous patterns in the dynamics of lemmings and voles are nonstationary in space and time. Furthermore, the similar patterns of change in both fox species indicate that persistence of cycles is governed by similar mechanisms in lemmings and voles.

National Category
Zoology
Identifiers
urn:nbn:se:su:diva-55132 (URN)10.5735/086.048.0305 (DOI)000292428100005 ()
Funder
Formas, 2009-563
Available from: 2011-03-02 Created: 2011-03-02 Last updated: 2017-12-11Bibliographically approved
2. Numerical responses and population decline of an avian predator dependent on cyclic prey
Open this publication in new window or tab >>Numerical responses and population decline of an avian predator dependent on cyclic prey
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Specialist predators per definition show numerical responses to changes in food supply. Numerical responses are broadly divided into a reproductive response, where reproductive output increases with increased food supply, and an aggregative response caused by breeding suppression and movements. Numerical responses are crucial for understanding predator-prey relations, and also for appropriate management of predator populations. Declining populations of keystone herbivores (voles and lemmings) have been described as a widespread pattern in Europe. Negative effects of dampened small mammal cycles on numerical responses, and thereby population dynamics, have been predicted but so far demonstrated for relatively few specialist predators. We therefore monitored relationships between a common sub-arctic avian predator, the rough-legged buzzard Buteo lagopus, and small rodents in NW Sweden for 19 years (1970-1978 and 2001-2010, 369 observed breeding attempts). Rough-legged buzzards were food-limited and exhibited aggregative and reproductive responses to current rodent abundance in both study periods, but with a weaker coupling in recent years. Density of breeding pairs in rodent peak years was 32-50 % lower in the 2000s than in the 1970s. Further, reproductive output was lower in the 2000s, possibly preventing a population increase. Mean clutch size decreased with 0.77 eggs/clutch (from 4.53 to 3.73, an 18 % reduction), and mean number of fledglings per breeding attempt decreased with 1.08 juveniles/pair (from 3.88 to 2.80, a decrease of 28%). Hatching success and brood survival did not change between 1970s and 2000s, which suggests that reproductive output is constrained by clutch size, rather than by nestling mortality. The observed changes in reproductive parameters support a long-term change in food supply at the onset of breeding as the causal factor. Our study demonstrates the link between predator-prey theory and the declining population-paradigm of conservation biology, illustrating how estimation of numerical responses can be used to predict the outcome of perturbations to predator-prey systems.

Keyword
Buteo lagopus, rough-legged, rodent cycles, population status
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-102725 (URN)
Available from: 2014-04-17 Created: 2014-04-17 Last updated: 2014-10-28
3. Functional responses of rough-legged buzzards in a multi-prey system
Open this publication in new window or tab >>Functional responses of rough-legged buzzards in a multi-prey system
2014 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 174, no 4, 1241-1254 p.Article in journal (Refereed) Published
Abstract [en]

The functional response is a key element of predator–prey interactions. Basic functional response theory explains foraging behavior of individual predators, but many empirical studies of free-ranging predators have estimated functional responses by using population-averaged data. We used a novel approach to investigate functional responses of an avian predator (the rough legged-buzzard Buteo lagopus Pontoppidan, 1763) to intra-annual spatial variation in rodent density in subarctic sweden, using breeding pairs as the sampling unit. the rough-legged buzzards responded functionally to norwegian lemmings (Lemmus lemmus l. 1758), grey-sided voles (Myodes rufocanus Sundevall, 1846) and field voles (Microtus agrestis L. 1761), but different rodent prey were not utilised according to relative abundance. the functional response to norwegian lemmings was a steep type II curve and a more shallow type III response to grey-sided voles. the different shapes of these two functional responses were likely due to combined effects of differences between lemmings and grey-sided voles in habitat utilisation, anti-predator behaviour and size-dependent vulnerability to predation. Diet composition changed less than changes in relative prey abundance, indicating negative switching, with high disproportional use of especially lemmings at low relative densities. Our results suggest that lemmings and voles should be treated separately in future empirical and theoretical studies in order to better understand the role of predation in this study system.

Keyword
Predation, rodent cycle, Lemmus, subarctic
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-102723 (URN)10.1007/s00442-013-2866-6 (DOI)000333171400017 ()
Available from: 2014-04-17 Created: 2014-04-17 Last updated: 2017-12-05Bibliographically approved
4. Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundra
Open this publication in new window or tab >>Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundra
Show others...
2010 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 1, 27-34 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-32481 (URN)10.1111/j.1600-0706.2009.17604.x (DOI)000273069000003 ()
Projects
Fjällräv
Available from: 2009-12-21 Created: 2009-12-10 Last updated: 2017-12-12Bibliographically approved
5. Carnivore conservation in practice: replicatedmanagement actions on a large spatial scale
Open this publication in new window or tab >>Carnivore conservation in practice: replicatedmanagement actions on a large spatial scale
Show others...
2013 (English)In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 50, no 1, 59-67 p.Article in journal (Refereed) Published
Abstract [en]

More than a quarter of the world’s carnivores are threatened, often due to multiple andcomplex causes. Considerable research efforts are devoted to resolving the mechanisms behindthese threats in order to provide a basis for relevant conservation actions. However, evenwhen the underlying mechanisms are known, specific actions aimed at direct support for carnivoresare difficult to implement and evaluate at efficient spatial and temporal scales.2. We report on a 30-year inventory of the critically endangered Fennoscandian arctic foxVulpes lagopus L., including yearly surveys of 600 fox dens covering 21 000 km2. These surveysshowed that the population was close to extinction in 2000, with 40–60 adult animalsleft. However, the population subsequently showed a fourfold increase in size.3. During this time period, conservation actions through supplementary feeding and predatorremoval were implemented in several regions across Scandinavia, encompassing 79% of thearea. To evaluate these actions, we examined the effect of supplemental winter feeding andred fox control applied at different intensities in 10 regions. A path analysis indicated that47% of the explained variation in population productivity could be attributed to lemmingabundance, whereas winter feeding had a 29% effect and red fox control a 20% effect.4. This confirms that arctic foxes are highly dependent on lemming population fluctuationsbut also shows that red foxes severely impact the viability of arctic foxes. This study also highlightsthe importance of implementing conservation actions on extensive spatial and temporalscales, with geographically dispersed actions to scientifically evaluate the effects. We note thatpopulation recovery was only seen in regions with a high intensity of management actions.5. Synthesis and applications. The present study demonstrates that carnivore populationdeclines may be reversed through extensive actions that target specific threats. Fennoscandianarctic fox is still endangered, due to low population connectivity and expected climate impactson the distribution and dynamics of lemmings and red foxes. Climate warming is expected tocontribute to both more irregular lemming dynamics and red fox appearance in tundra areas;however, the effects of climate change can be mitigated through intensive managementactions such as supplemental feeding and red fox control.

Keyword
Alopex, arctic, climate, extinction, population cycles, restoration, SEFALO, Vulpes
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-87916 (URN)10.1111/1365-2664.12033 (DOI)000314520500008 ()
Available from: 2013-02-25 Created: 2013-02-25 Last updated: 2017-12-06Bibliographically approved

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Citation style
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