Predation, competition and conservation: An investigation of the behavioural ecology of the internationally-protected Geomalacus maculosus
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The Kerry spotted slug Geomalacus maculosus is protected internationally on the basis of its limited global distribution in that it occurs only in the west of Ireland and north-western Iberia. Spanish populations are listed as ‘Vulnerable’ and may be severely threatened. Conversely, the distribution of G. maculosus in Ireland has increased in recent years, where its conservation status is listed as ‘Least Concern’. Once thought to be a highly sensitive species restricted only to peatlands and semi-natural woodlands within Ireland, G. maculosus populations have recently been found thriving in modified habitats such as commercial conifer plantations. Geomalacus maculosus is a highly abundant species where it occurs in Ireland, suggesting that it may possess a broader capacity for survival than previously considered. While some information exists on environmental factors which influence the distribution and abundance of G. maculosus, no studies to-date have examined the contribution of biotic factors, such as predation and competition, to the ecology of this species. This thesis aims to improve our knowledge of the behaviour, ecology and conservation needs of G. maculosus by investigating particular traits which might enable it to survive and increase its distribution in Ireland. Firstly, the puzzling issue of colour dimorphism was investigated with the hypothesis that G. maculosus exhibits habitat-specific camouflage. Secondly, interactions between G. maculosus and sympatric slug species in conifer forests were examined to determine the ecological position of G. maculosus within the wider gastropod community. Thirdly, the defensive capabilities of G. maculosus in response to predation by carabid beetles were studied to better understand the susceptibility of G. maculosus to predation. Overall, the results presented throughout this thesis suggest that G. maculosus is welladapted to survive in both open and forested habitats (including commercial forestry) and possesses a broader niche in Ireland than was previously recognised. However, it also highlights threats to the conservation of this species which have not been previously considered.