Coexistence, habitat patterns and the assembly of ant communities in the Yasawa islands, Fiji

Community assembly rules are important to help understand the dynamics of biological invasions. The coexistence of native and invasive ant species was examined by litter sampling on six remote islands within the Fijian archipelago, in the Pacific Ocean. The composition of ant assemblages of the islands and also of three different habitats across islands was very similar to each other. Estimates of species richness indicated that the sampling effort had generally captured a large proportion of ant species (60–97%). Analysis at two different spatial scales (regional [islands within an archipelago], and local [plots within an island]) and on two null model data sets (co-occurrence and body size), showed that the majority (10 of 12) of assemblages were not different from randomly assembled communities. Habitat type played an important role in the co-occurrence patterns. Scrub and coconut habitats, which are non-native habitats and frequently disturbed (i.e. harsh environments), strongly influenced the assembly of the ant community. However, two invasive species, Pheidole megacephala and Anoplolepis gracilipes may have also shaped the ant communities through inter-specific competition. These two species excel at both the discovery and domination of resources, and could have ‘disassembled’ the native ant fauna. Recent surveys and ecological studies from other Pacific islands show that a very similar set of invasive species to the Yasawa islands are ubiquitous throughout the region. Thus, similar patterns of competition, co-occurrence and community organisation that exist in the Yasawa islands could be manifested throughout the Pacific Ocean region.