The effects of forest cover change and polydomous colony organisation on the wood ant Formica lugubris

Anthropogenic land use changes, such as deforestation, generally have negative effects on ecosystems. However, in Europe recently, historic trends in deforestation are being reversed due to increases in planted forests, and it is becoming much rarer to replace native forests with plantations. British forests have undergone centuries of degradation and fragmentation, and increases in forest cover due to plantations represent a potential positive for forest specialist species struggling in isolated fragments. In this thesis, I assess forest cover change and the demographic and genetic health of populations of the wood ant Formica lugubris, a forest specialist, in the North York Moors National Park, UK. I show that, contrary to expectations, non-native conifer plantations have had incredibly beneficial effects on this forest specialist species. Populations of F. lugubris have expanded from historically isolated fragments, and show no evidence of this expansion ceasing. Furthermore expanded populations are genetically diverse in both nuclear and mitochondrial DNA, and show evidence of commercial forests connecting previously isolated population fragments. There is strong divergence within mitochondrial DNA across the landscape in F. lugubris, which suggests either a cryptic species within the study population, or an historic hybridisation event. Formica lugubris exhibits polydomous colony organisation, whereby multiple spatially separate nests display social and cooperative connections, and are therefore one colony. I show that socially connected nests are socially and cooperatively distinct from their neighbouring colony, but show no equivalent genetic distinction. The findings within this thesis support growing evidence that non-native conifer plantations can have positive effects on forest biodiversity, and that some wood ant populations within the UK are healthy and under no threat of extinction. Furthermore polydomous colonies are cooperative but not genetic units, and division of colonies in this species may be ecologically, rather than genetically determined.