Monoculture plantations are replacing native forests and expanding globally due to increasing demand for cash crops. Decrease of plant diversity in monoculture plantations can reduce prey abundance which may ultimately alter nutrient availability and impact feeding ecology of predators. These changes in nutrient availability can impact organisms which need to maintain proper nutrient balance to limit drops in performance and sustain population growth. In this study, we examined if ants have different feeding preferences in exotic monoculture plantations relative to native forests, using L. confertus plantations and secondary forests in Hong Kong as the study system. We predicted that conspecific ants would be more protein-limited in L. confertus plantations relative to secondary forests. To test this prediction, we hypothesized that native conspecific ants would have 1) lower trophic positions and 2) stronger feeding preference for protein-baits in exotic plantations. The trophic position of ants was estimated using stable isotope analysis; while a cafeteria experiment was conducted to quantify ant preference between protein (chicken), carbohydrates (sugar concentration of ~20%) and sodium (cooking salt concentration of ~0.5%) baits in L. confertus plantations and secondary forests.
From a total of 35 species recorded in this study, 19 were collected in both habitats. Stable isotope analysis showed that trophic positions of conspecific ants dropped significantly (~0.5 trophic position) from secondary forest to L. confertus plantations. Relative abundance of conspecific ants on protein baits was significantly higher (~7%) in L. confertus plantations in comparison to secondary forests. Our results demonstrate that though some ant species can inhabit both habitats, in L. confertus plantations the diets of most species are significantly altered and more protein-limited. This might be explained by the reduced abundance of prey as shown in previous studies. Failure in maintaining nutrient balance may decrease animal performance which could lead to a reduction in the efficacy of their role in regulating ecosystem-level nutrient dynamics. To test if ant colony-level performance is lower in L. confertus plantations relative to secondary forests, future work will focus on a comparison of body and colony size of conspecific ants in these two habitats.