Habitatselektion von zwei Waldameisenarten (Formica rufa und F. polyctena)

Habitat selection of two wood ant species (Formica rufa and F. polyctena) Wood ants play an important role in the forest ecosystem, but knowledge about their spatial distribution is often outdated or scarce in Switzerland. Species-specific habitat requirements remain poorly understood, especially for the two sympatric species Formica rufa and F. polyctena, preventing the development of efficient conservation measures. Following the survey of wood ant mounds in the cantons of Basel-Landschaft and Basel-Stadt of 2015/2016, we developed a predictive hierarchical habitat model to investigate the relationships between habitat characteristics (slope, canopy cover, canopy height, vertical structure, distance to forest edge, distance to forest roads, proportion of conifers, and proportion of forest area) and the nest density of F. rufa and F. polyctena. By doing so, we adjusted for imperfect detectability of our census method. Most of the habitat factors have been derived from remote-sensing data (LiDAR, false-color images). We found that the two species differ in their smallscale habitat preferences, especially regarding canopy cover, slope and distance to forest edge. Compared to F. polyctena, F. rufa has less marked habitat preferences and is relatively indifferent to canopy height, proportion of forest area and distance to forest edge. Our results are inconsistent with the claim from other studies that F. rufa occurs more frequently at forest edges than F. polyctena. Furthermore, our study emphasizes the need to take into account the detection probability for a large-scale survey of wood ant mounds.