ANT COMMUNITIES IN TAIGA CLEARCUTS - HABITAT EFFECTS AND SPECIES INTERACTIONS

We surveyed the structure of ant communities in young taiga forests by pitfall trapping in southern Finland. The sampling sites were clearcu t and planted with conifers 14-20 yr before the sampling. The results indicated that the structure of the ant communities was largely determ ined by the top competitors, the territorial species of the wood-ant g roup (Formica aquilonta and F. lugubris) in the older, and the aggress ive slavemaking ant (F. sanguinea) in the younger clearcuts. Species i nteractions resulted in distinct spatial distributions of individual s pecies depending on the competitive status of the species concerned. C ompetition and slavemaking were the most important factors on larger s patial scales. The spatial scale of competitive structuring was determ ined by the territory and colony sizes of the top competitors. On a fi ner scale, variability in moisture and tree-canopy shading seemed to h ave enhanced coexistence of some competing submissive species by allev iating the effects of nest-site competition and slavemaking. Competiti on between the wood ants and the slavemaking ant affected indirectly t he distribution and abundance of the species subject to slavemaking, F . fusca and F. lemani. Similarly, the top competitors presumably affec ted the distributions of other interacting subordinate species indirec tly through differential competitive effects on them. Overall, species interactions seemed to have induced considerable determinism in ant-c ommunity succession in young forests.