Wood ants (Formicidae, Insecta) at the alpine tree-line ecotone: negative and positive associations with other arthropods

Wood ants are dominant insects in coniferous forests that interact with many other
organisms, thereby significantly shaping the presence and behavior of other species.
These interactions can be either positive, like in the case of trophobiotic mutualisms,
or negative in cases of competition or predation. We investigated associations of wood
ant prevalence with ground beetles, spiders and harvestmen, and plant lice along a
natural density gradient of wood ants over the elevational tree line ecotone in the southern
Central Alps. Plant lice were found to be positively associated with wood ants (r
= 0.38), in contrast to spiders and harvestmen that tended to occur at lower densities
where wood ants were more prevalent (r = -0.45.). Ground beetle individual numbers
showed no pattern in relation to wood ants, but their community composition displayed
an interesting geographic segregation. Both ground beetles and spiders showed no
significant reaction to the wood ant density regarding their community composition.