Local co-occurrence of several highly invasive ants in their native range: are they all ecologically dominant species?

Abstract

An important goal of invasion ecology is to understand the colonization, establishment, and spread of exotic species. To accomplish this, it is essential to examine the ecology of introduced species in native populations. We examined organization patterns, spatial structure, and competitive abilities of ground-dwelling ants in different habitats of a protected area in east-central Argentina, where several highly invasive ant species naturally coexist, to determine whether all they are ecologically dominant in their native range as in their introduced range. We sampled ant communities at Otamendi Nature Reserve and found 49 ant species co-occurred with moderate separation among habitats, including five species that are global invaders; but only Solenopsis richteri (the most numerically dominant) and Linepithema humile (the best mass recruiter) were ecologically co-dominant along with another three non-invasive species in locally rich assemblages. Their co-occurrence was apparently facilitated by both niche and competitive differences. However, we found no evidence for discovery-dominance trade-offs, and ant diversity and spatial segregation suggested that competition only plays a secondary role in structuring assemblages in arboreal habitats. Despite L. humile and S. richteri were ecologically co-dominant, their hegemony was lower in the reserve than in their introduced range likely due to biotic resistance. The other invasive ants (Wasmannia auropunctata, Brachymyrmex patagonicus, and Nylanderia fulva) were not dominant. It is possible that their establishment, persistence, and high prevalence in anthropic habitats in native and introduced populations to be attributed to their better physiologic adaptations to disturbed habitats rather than to their superior competitive abilities.