Stable and radio-isotopic signatures reveal how the feeding habits of ants respond to natural secondary succession in a cool-temperate forest

Ants are known to have various feeding habits and play important roles in many terrestrial ecosystems. However, little is known about how the feeding habits of each ant species are affected by the environmental changes associated with forest succession. In this study, we examined how feeding habits as well as the species composition and food preference of ants would respond to 105-year-old natural secondary succession of a cool-temperate forest. Stable carbon and nitrogen isotopes and radiocarbon were used to infer the feeding habits. The species richness was not affected by forest stand age. Redundancy analysis indicated that stand age, litter N concentration, and soil microbial respiration had significant relationships with the ant species composition. The bait experiments showed that honey bait became more attractive to ants relative to tuna bait in late succession. This was probably associated with changes in available food resources, such as nectar, during succession. Although the isotopic signatures differed significantly among the sample types (i.e., ant species, canopy leaves, and leaf litter), they were not significantly affected by forest stand age or by the interaction between sample types and stand age. This indicates that the ants showed consistent differences in feeding habits among the species during succession. Our results suggest that despite great changes in vegetation, each ant species would maintain functional roles in C and N flows during forest succession.