Grazing ecology, parasitism and performance of Soay sheep on St. Kilda

<p>This is my PhD thesis. It's dated 2003 but was awarded in 2004. Here is the abtract:</p> <p> </p> <p>(1) This thesis considers several aspects of the herbivore-forage-parasite interaction of feral Soay sheep (<em>Ovis aries</em> L.), their food source, and their gastro-intestinal (GI) parasites, on the island of Hirta (St. Kilda), Scotland. The main variables that affect performance are diet quality, parasite burden, and weather effects. The effects of these parameters may cross generations via the effect on maternal condition and lactation quality.</p> <p>(2) A description of seasonal patterns of diet composition and quality is presented. This is followed by an assessment of seasonality and density dependence in the composition, and quality, of available forage, and of net primary productivity.</p> <p>(3) The role of seasonality, population density, and spatial scale, in the assessment of distribution and selectivity patterns is then considered. The spatial scale at which the analyses are made has a huge influence on the results, and thus the scale at which assessments are made should be carefully considered. Techniques using hierarchical cluster analysis were employed to select appropriate spatial scales, with promising results.</p> <p>(4) After this, the effects of maternal characteristics and environmental variables on offspring survival and birth weight are examined. Terms for weather severity and forage quality during gestation, both remained in the models alongside population density, thus indicating the presence of weather effects and both interference and exploitation competition. Maternal condition and GI parasite burden were also important factors. These results have an important bearing on the population dynamics of the system, because juvenile recruitment is one of the key parameters in the population dynamics of large herbivores.</p> <p>(5) An experiment investigating the effects of GI parasites on foraging behaviour found no evidence of parasite induced anorexia or of any parasite induced changes in diet composition in Soay sheep. However, a mean intake rate estimate of 689gDM/day was made which compares well with estimates from Scottish Blackface sheep.</p> <p>(6) Finally, the consequences and limitations of these findings are assessed and areas requiring further study are highlighted.</p> <p> </p> <p><em>Note: there are a few Endnote formatting errors - sorry about that!</em>