Survival of the trunk ant (Formica truncorum Fabricius, 1804; Hymenoptera: Formicidae) in a fragmented habitat

In The Netherlands the trunk ant (Formica truncorum FABRICIUS, 1804) occurs at the edge of its distributional range. It is present in a restricted area of 200 km², although more habitat is present in the whole eastern part of the country. Its scattered distribution pattern changes in time. The aim of the study was to assess the regional persistence of a metapopulation of this species on the basis of change in the occupancy of habitat patches over a period of seven years. The perimeter and connectivity of a habitat patch are the best predictors for its occupancy. Occupancy of habitat patches is negatively correlated with their distance to all occupied patches, as well as to the core patch. However, the core patch is shrinking, due to succession of the vegetation. Habitat loss was also observed in many other habitat patches, which implies decreasing connectivity. The most effective way of increasing the regional survival probability of the trunk ant is by enlarging existing patches, improving their habitat quality and ensuring that they form part of a cohesive habitat network.