Aims Colonization by non-native ants represents one of the gravest potential threats to island ecosystems. It is necessary to identify general mechanisms by which non-native species are able to colonize and persist in order to inform future prevention and management. We studied a model-island assemblage of 17 non-native ant species with aim of identifying the spatial source of introductions and assessing how such a diversity of species are able to coexist.

Location Data were collected on Ascension Island: an ideal study system for its intermediate area, compact shape, spatial heterogeneity, lack of native ant species, and availability of non-native ant records dating back to the 1800s.

Methods We collected over 47,000 individual ants from 73 sites using a range of baited traps and survey techniques. We combined this novel data with past occurrence records in order to determine whether human settlements have historically been the source of ant introductions and to quantify the mean rate at which species have dispersed across the island. Analysis of standardized field data revealed the extent to which ants were partitioning ecological niche space via (1) habitat separation, (2) fine-scale resource partitioning and (3) climatic heterogeneity.

Results Ants were radiating at a linear rate of approximately 0.5 km2 per year from human settlements on this island, with the most widespread species having been introduced earliest. After accounting for incomplete colonization, we found no evidence to suggest habitat separation between species. Instead, we found significant niche separation through resource partitioning and weather-dependent activity patterns.

Main Conclusions Our results indicate that non-native ants can coexist in very close proximity and are therefore capable of existing at great diversity on even small islands. It is inevitable that ant colonization will continue without increased biosecurity measures, habitat restoration around settlements and conservation of native species populations.