Nesting preferences of the threatened wood ant <Emphasis Type="Italic">Formica exsecta</Emphasis> (Hymenoptera: Formicidae); implications for conservation in Scotland

Wood ants are a dominant and ecologically important component of northern coniferous forests with interactions at many trophic levels. Each species exhibits specific habitat preferences which need to be understood if conservation measures are to be successful. In Britain, the rare narrow-headed ant Formica exsecta has disappeared from much of its former range and is now largely restricted to the highlands of Scotland where it is found in open canopy woodland and along forest edges. Nest locale of one small and vulnerable population at the edge of its current range, were compared with those of random locations within the same habitat and with actual nests within the stronghold of the Abernethy-Glenmore complex in Strathspey. After data exploration with Redundancy Analysis, stepwise multiple regression was used to create a model which best estimated the variance in nest location using a parsimonious selection of vegetation and environmental variables. The input variables included were light, soil moisture, altitude, tree stature and distribution, vegetation structure and composition, and ground characteristics. F. exsecta clearly exhibited preferences for the position of nest mounds in relation to light, vegetation and tree cover. Forest location was also important in determining which variables nests were affected by. This study highlights the importance of maintaining a dynamic mosaic of different-aged woodland enabling early successional species such as F. exsecta, with suitable areas to move to as conditions change and allowing the co-existence of all wood ant species.