Long-term impact of agriculture on the survival of wood ants of the Formica rufa group (Formicidae)

The impact of agriculture on wood ants of the Formica rufa group was investigated in a small-scale agricultural landscape with many woodland fragments in the east of the Netherlands. An inventory of nests was carried out in 1986, and repeated in 2014. The number of nests of F. rufa and F. polyctena had drastically decreased during the intervening 28 years, especially in small patches of woodland bordering a maize field. The species F. rufa, which mainly disperses by flight of the queen, seems to be better adapted to habitat fragmentation than F. polyctena, where dispersal is mainly by colony splitting. However, the flying strategy can only be successful in a landscape where most woodland fragments have a good quality habitat; in the study area, the habitat quality had deteriorated. This is ascribed to the development of a tall, nitrophilous vegetation, a result of considerable nitrogen deposition from the atmosphere and the spraying of manure. The regional survival of wood ants in the east of the Netherlands is at risk in the agricultural landscapes we studied. This is due to the increasing probability of colonies becoming extinct and the decreased probability of a queen colonizing habitat patches. However, the negative influence of agriculture on the edge vegetation of patches of woodland can be decreased by leaving a wide strip between the arable land and the woodland that receives no manure.