Ghosts of the past: flightless saproxylic weevils (Coleoptera: Curculionidae) are relict species in ancient woodlands

Historic maps show that the Central European landscape was influenced by exploitive human land-use during the middle ages and in the following centuries. A mixture of ancient woodlands, which survived the period of woodland destruction, and recent woodlands, which were established after 1800, cover about 10% of the study area in NW Germany today. Weevils (Coleoptera: Curculionidae) of the subfamily Cryptorhynchinae with the genera Acalles, Kyklioacalles, Ruteria and of the subfamily Molytinae, tribe Acicnemidini with the genus Trachodes are all flightless and possibly influenced by landscape history. The aims of this investigation are (1) to examine the spatial distribution of flightless saproxylic weevils in ancient and recent woodlands in NW Germany and (2) to test the frequency of possible relict species in relation to historical and current woodland size. Based on a field study in 29 deciduous woodlands and species records in collections and literature, six flightless saproxylic weevils were found to be associated with ancient woodlands in NW Germany. None of these were recorded in any of the 14 recent woodlands studied. The frequency of these relict species is correlated with historical, but not with current, woodland size. Distribution maps for Lower Saxony and data on the phenology of the relict species are presented. These weevils are relict species of ancient woodland, because they were unable to colonise isolated woods that were established after 1800. All of them are dependent on dead or dying wood for larval development. The results show that ancient broadleaved woodlands with long-lasting habitat continuity are of high conservation value for invertebrate species such as saproxylic weevils.