Environmental filtering drives patterns of ant species richness and activity across Hawaiian coffee farms.

Ants perform diverse ecological functions in agricultural systems, yet in Hawai'i, all established ant species are thought to be introduced, creating novel communities shaped by environmental conditions. We examined how coffee-growing district and microclimate structure invasive ant communities in Hawaiian coffee agroecosystems. Ants were surveyed across 15 coffee farms on Hawai'i Island spanning a 600-m elevational gradient and 2 growing districts (Kona and Ka'ū). We quantified ant species richness, activity, and tree-level occupancy and evaluated associations with district, elevation, rainfall, temperature, and humidity. We recorded 22 ant species across 3 subfamilies, with Brachymyrmex obscurior, Ochetellus glaber, Pheidole megacephala, Plagiolepis alluaudi, and Tapinoma melanocephalum being the most common species. Ant species richness, activity, and tree-level occupancy were significantly higher in Kona compared to Ka'ū and declined with increasing annual rainfall. Activity of several common species was positively associated with overall species richness, while no common species showed a strong negative association with richness. These results suggest that environmental filtering, rather than competitive dominance, structures invasive ant communities in Hawaiian coffee systems. Our findings indicate that invasive ants are most active and widespread in warmer, drier coffee farms, where they may exert their strongest ecological effects. These results provide baseline information for understanding the distribution of ants in Hawaiian coffee agroecosystems and establish a foundation for future research evaluating ant-mediated pest suppression, mutualisms, and other ecosystem services and disservices in coffee production.