Interspecific Aggression and Resource Monopolization of the Invasive Ant Anoplolepis gracilipes in Malaysian Borneo

Abstract

Invasions by introduced ant species can be ecologically destructive and affect a wide range of taxa, particularly native ants. Invasive ant species often numerically dominate ant communities and outperform native ant species in effective resource acquisition. Here, we describe interactions between the invasive ant Anoplolepis gracilipes (Smith) and resident ant species in disturbed habitats in NE Borneo. We measured interference competition abilities of A. gracilipes by performing arena bioassays between two A. gracilipes colonies and seven local ant species, and measured its effective resource competition at baits within supercolonies and at supercolony boundaries. Furthermore, we compared ant species diversity and composition at baits among (A) core areas of A. gracilipes supercolonies, (B) supercolony boundaries and (C) outside supercolonies. Anoplolepis gracilipes was behaviorally dominant over most ant species except Oecophylla smaragdina. Within supercolonies, A. gracilipes discovered all food baits first, and monopolized the vast majority throughout the course of the experiment. At supercolony boundaries, A. gracilipes discovered baits later than resident ant species, but subsequently monopolized half of the baits. Furthermore, the activity and diversity of the ant community within A. gracilipes supercolonies was lower than at its boundaries and outside supercolonies, and the ant communities differed significantly between infested and noninfested areas. Our study supports the hypothesis that successful establishment of A. gracilipes in anthropogenically disturbed habitats may negatively affect resident ant communities through high levels of direct interspecific aggression and almost complete monopolization of resources within high-density supercolonies.