Land use and population regulation : vole dynamics in a grazing experiment

Land use is the major global driver of biodiversity loss and ecosystem change. In this thesis the impact of an important land use practice, livestock grazing, in the population dynamics of a keystone species of temperate grassland ecosystems, the field vole Microtus agrestis, was investigated in a manipulative grazing experiment in the UK uplands. Vole densities at different spatial scales declined with increasing grazing intensities. This decline was especially acute and non-linear at high altitudes, where the preferred habitat of voles is less abundant. The activity of an important vole predator, the red fox Vulpes vulpes, declined accordingly. The evidence suggested that the availability of voles to foxes changed between grazing treatments. A behavioural response to reduced habitat quality was the most likely mechanism to explain vole declines with grazing, while food limitation or increased predation received no support as valid mechanisms to explain vole declines. Grazing increased vole mobility, changed sex-specific patterns of natal dispersal, affected the age structure of the female population and led to biases in sex ratios amongst the adult population. Despite profound demographic changes, the dynamics of the vole population was unaffected by grazing. Neither direct nor delayed density dependent dynamics nor seasonal dynamics changed between grazing treatments. Apparent survival in adults was not direct density dependent and similar in ungrazed and grazed areas. Negative direct density dependence in reproductive and immigration rates, and population growth rates at different spatial scales was strong and did not change in response to grazing. Thus, livestock grazing reduced vole densities probably through a behavioural response to grazing, but it did not affect the demographic mechanisms of population regulation or vole population dynamics.EThOS - Electronic Theses Online ServiceGBUnited Kingdo