Forest invader replaces predation but not dispersal services by a keystone species

Invasive species generally occur and thrive in human-disturbed ecosystems, but Brachyponera chinensis (Asian needle ant, formerly ‘ Pachycondyla chinensis ’) also invades intact forests. The invasion into native habitats potentially puts B. chinensis in direct competition with the keystone seed-dispersing ants in the genus Aphaenogaster . We observed B. chinensis colonizing artificial nests placed in deciduous forest of the north Georgia Piedmont (US). Their presence appeared to displace existing Aphaenogaster rudis and Reticulitermes flavipes (subterranean termite) colonies. We subsequently mapped the B. chinensis invasion as well as co-existing A. rudis and R. flavipes colonies by examining coarse woody material (CWM) for nesting colonies. We tested whether the B. chinensis invasion changed with forest microclimates, covaried with A. rudis and/or R. flavipes occurrence, and whether it was associated with failed dispersal of a dominant understory herb. Our results and observations suggest that B. chinensis shares ecological niche requirements (temperature, moisture and CWM as nesting habitat) with A. rudis , severely diminishing the abundance of this native ant. In supplanting A. rudis , B. chinensis appears to play an equivalent role to A. rudis as a termite predator, but fails as a seed disperser. Essentially, the invader substitutes for the negative but not the positive species interactions, thereby apparently shifting ecological dynamics in the invaded system.