1. Epigeic ants are functionally important arthropods in tropical and subtropical forests, particularly by acting as predators. High predation pressure has been hypothesised to be a mechanism facilitating high diversity across trophic levels.

2. In this study, standardised pitfall traps were used in a highly diverse subtropical forest to test if and how ant species richness is related to tree species richness and a comprehensive set of other environmental variables such as successional age, soil properties or elevation.

3. A total of 13 441 ant individuals belonging to 3839 species occurrences and 71 species were collected, of which 26 species were exclusive predators and 45 species were omnivores.

4. Occurrence and species richness of total and omnivore ants were positively related to soil pH. Predator ant occurrence was unrelated to all environmental variables tested.

5. The species richness of predator ants increased with tree species richness but decreased with leaf functional diversity and shrub cover. Elevation negatively influenced only total ant species richness.

6. The evenness of predators increased with tree species richness, while the evenness of all ants decreased with shrub cover. Omnivore ant evenness decreased with tree evenness, but increased with successional age.

7. The results highlight the value of diverse forests in maintaining species richness and community evenness of a functionally important predator group. Moreover, the results stress the importance of analysing trophic groups separately when investigating biodiversity effects