Population dynamics of feral goats on the Isle of Rùm, NW Scotland: the stresses of coping with a high latitude environment

Feral goats are an invasive species renowned for their ability to survive in a wide variety of habitats. However, their capacity to occupy high latitude habitats is severely restricted. To determine why, I analyse data on the lifehistory and demography of a feral goat population on the Isle of Rùm, NW Scotland, in relation to both longterm variation in climatic variables and within-population variation in environmental variables. Mortality and fecundity rates are sensitive to variations in winter thermal conditions. Giving birth in mid-winter imposes significant stress on both mother and kid, although the effect may be ameliorated by the ability to find shelter (especially beach-level caves) and higher quality forage in heath habitats. Longterm patterns in population growth rates are correlated with winter temperature and the North Atlantic Oscillation index, with little evidence for density-dependent effects. There is, however, evidence that the presence of a large sympatric red deer population has limited the goats’ capacity to increase by denying them access to preferred foraging habitat. Climate warming is likely to have a beneficial impact on high latitude goat populations.