Abstract
Grazing by domestic ungulates has substantial impacts on ecosystem structure and composition. In grasslands of the northern hemisphere, livestock grazing limits populations of small mammals, which are a main food source for a variety of vertebrate predators. However, no experimental studies have described the impact of livestock grazing on vertebrate predators. We experimentally manipulated sheep and cattle grazing intensity in the Scottish uplands to test its impact on a relatively abundant small mammal, the field vole (Microtus agrestis), and its archetypal generalist predator, the red fox (Vulpes vulpes). We demonstrate that ungulate grazing had a strong consistent negative impact on both vole densities and indices of fox activity. Ungulate grazing did not substantially affect the relationship between fox activity and vole densities. However, the data suggested that, as grazing intensity increased i) fox activity indices tended to be higher when vole densities were low, and ii) the relationship between fox activity and vole density was weaker. All these patterns are surprising given the relative small scale of our experiment compared to large red fox territories in upland habitats of Britain, and suggest that domestic grazing intensity causes a strong response in the activity of generalist predators important for their conservation in grassland ecosystems.
Highlights
Domestic ungulate grazing intensity has important impacts on natural communities of grassland ecosystems (Diaz et al, 2007; Fleischner, 1994; Patra et al, 2005; Vickery et al, 2001)
We use data from a replicated grazing experiment in the uplands of Scotland to quantify the impact of grazing intensity on cyclically-fluctuating field voles and an archetypal generalist vole predator in these ecosystems, the red fox (Kjellander and Nordstrom, 2003; Leckie et al, 1998; Lindstrom, 1989; O’Mahony et al, 1999)
We predicted that increasing grazing intensity would reduce field vole densities, but that red fox activity would peak at intermediate grazing intensities where the combination of low vegetation cover and intermediate vole abundance might maximise vole availability
Summary
Domestic ungulate grazing intensity has important impacts on natural communities of grassland ecosystems (Diaz et al, 2007; Fleischner, 1994; Patra et al, 2005; Vickery et al, 2001). We use data from a replicated grazing experiment in the uplands of Scotland to quantify the impact of grazing intensity on cyclically-fluctuating field voles and an archetypal generalist vole predator in these ecosystems, the red fox (Kjellander and Nordstrom, 2003; Leckie et al, 1998; Lindstrom, 1989; O’Mahony et al, 1999). We use this model system to test the hypothesis that livestock grazing intensity impacts on the activity of generalist vertebrate predators in upland grasslands. We predicted that fox activity at any given vole density would be larger at intermediate grazing intensities
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