Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern England: the role of vole‐eating raptors

Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern... 1. The regional synchrony hypothesis (RSH) states that synchrony in microtine abundance over large geographical areas is caused by nomadic avian predators that specialize on small mammals for food. This has proved a difficult hypothesis to test because experiments at an appropriate scale are almost impossible. 2. We used the decline of the most abundant, nomadic vole‐eating raptors in an extensive conifer forest in northern England (Kielder Forest) as a natural experiment to evaluate their influence on synchronizing voles at different spatial scales. Field vole populations fluctuated on a 3–4‐year cycle of abundance, similar to the periodicity in central Fennoscandia. 3. Over a 23‐year period, the combined numbers and density of kestrels and short‐eared owls significantly declined. If these raptors were responsible for synchronizing vole abundance, the decline should have been associated with a decrease in synchrony. We could find no change in synchrony during the period of the greatest decline in kestrel and short‐eared owl numbers (1980–97). 4. In Kielder, vole abundance has been shown to change in a wave‐like manner, with synchrony in the direction of the wave being 5–10‐fold smaller than that reported in Fennoscandia. Tawny owls are sedentary and the most abundant vole‐eating raptor in our study area, and might have an equalizing influence on vole abundance over smaller areas if they foraged in a density‐dependent manner and responded functionally to increasing vole density. If this was the case, spatial variability in vole density should have been less in occupied than unoccupied owl territories, especially in years of low vole density when owls could take a larger proportion of the standing crop of voles. Even though tawny owls caught a significant proportion of the vole population, we could find no difference in variation in vole density between owl territories that were unoccupied, occupied with no breeding attempt, or occupied with a successful breeding attempt. 5. We conclude that the small‐scale synchrony in field vole abundance is unlikely to be caused by avian predators. Instead, it is more likely to be related to the pattern of clear‐cutting that has developed in Kielder, which restricts vole dispersal. If this assumption is correct, we would predict more widespread synchrony in vole abundance in first‐generation forests when extensive areas are planted over short periods of time, and this is supported by anecdotal evidence. These conclusions indicate that foresters may be able to manipulate the spatial dynamics of voles and vole predators by varying patch sizes within forests. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Ecology Wiley

Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern England: the role of vole‐eating raptors

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Publisher
Wiley
Copyright
Copyright © 2000 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0021-8901
eISSN
1365-2664
DOI
10.1046/j.1365-2664.2000.00473.x
Publisher site
See Article on Publisher Site

Abstract

1. The regional synchrony hypothesis (RSH) states that synchrony in microtine abundance over large geographical areas is caused by nomadic avian predators that specialize on small mammals for food. This has proved a difficult hypothesis to test because experiments at an appropriate scale are almost impossible. 2. We used the decline of the most abundant, nomadic vole‐eating raptors in an extensive conifer forest in northern England (Kielder Forest) as a natural experiment to evaluate their influence on synchronizing voles at different spatial scales. Field vole populations fluctuated on a 3–4‐year cycle of abundance, similar to the periodicity in central Fennoscandia. 3. Over a 23‐year period, the combined numbers and density of kestrels and short‐eared owls significantly declined. If these raptors were responsible for synchronizing vole abundance, the decline should have been associated with a decrease in synchrony. We could find no change in synchrony during the period of the greatest decline in kestrel and short‐eared owl numbers (1980–97). 4. In Kielder, vole abundance has been shown to change in a wave‐like manner, with synchrony in the direction of the wave being 5–10‐fold smaller than that reported in Fennoscandia. Tawny owls are sedentary and the most abundant vole‐eating raptor in our study area, and might have an equalizing influence on vole abundance over smaller areas if they foraged in a density‐dependent manner and responded functionally to increasing vole density. If this was the case, spatial variability in vole density should have been less in occupied than unoccupied owl territories, especially in years of low vole density when owls could take a larger proportion of the standing crop of voles. Even though tawny owls caught a significant proportion of the vole population, we could find no difference in variation in vole density between owl territories that were unoccupied, occupied with no breeding attempt, or occupied with a successful breeding attempt. 5. We conclude that the small‐scale synchrony in field vole abundance is unlikely to be caused by avian predators. Instead, it is more likely to be related to the pattern of clear‐cutting that has developed in Kielder, which restricts vole dispersal. If this assumption is correct, we would predict more widespread synchrony in vole abundance in first‐generation forests when extensive areas are planted over short periods of time, and this is supported by anecdotal evidence. These conclusions indicate that foresters may be able to manipulate the spatial dynamics of voles and vole predators by varying patch sizes within forests.

Journal

Journal of Applied EcologyWiley

Published: Sep 1, 2000

References

  • Consequences of large‐scale processes for the conservation of bird populations
    Baillie, Baillie; Sutherland, Sutherland; Freeman, Freeman; Gregory, Gregory; Paradis, Paradis
  • Merlins Falco columbarius in Kielder Forest: influences on breeding performance
    Little, Little; Davison, Davison; Jardine, Jardine
  • Variation in digestion of prey by the tawny owl ( Strix aluco )
    Lowe, Lowe
  • Use of coupled oscillator models to understand synchrony and travelling waves in populations of the field vole Microtus agrestis in northern England
    Sherratt, Sherratt; Lambin, Lambin; Petty, Petty; MacKinnon, MacKinnon; Coles, Coles; Thomas, Thomas

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