Trophic interactions of ants are robust to tree species loss

Joshua Emil Spitz, Annika Leah Langlotz, Julian Lunow, Steffen Seitz, Xianglu Deng, Xiaojuan Liu, Heike Feldhaar, Michael Staab

1. How changes in habitat conditions influence insect diversity has been intensively studied. However, whether trophic interactions of insects are also influenced by such changes is largely unknown. Higher habitat heterogeneity is often hypothesized to promote niche partitioning and complementarity in resource use among interacting species, yet evidence from animal interaction networks is sparse.
2. We tested in a biodiversity experiment how experimentally-manipulated tree species richness influences ant-nutrient interaction networks using a replicated and standardized set of nutrient baits. The structure of ant-nutrient networks was quantified with selected quantitative network indices representing diversity, redundancy and specialization of interactions.
3. Contrary to expectations, tree species richness had no direct or indirect effects on network complementarity. Instead, diversity of interactions declined slightly with increasing tree species richness, while network redundancy and specialization did not change. This indicates that higher tree diversity may influence the diversity of trophic links, possibly through altered competitive dynamics in more diverse ant assemblages, but not overall network structure.
4. These patterns are consistent with nutrient regulation theory predicting that foragers should concentrate interactions on resources that best satisfy the nutritional targets of colonies, reducing interaction diversity when nutritionally relevant resources are readily available. Our results suggest that for trophic networks of ants, habitat heterogeneity alters interaction frequencies rather than promoting complementarity or structural reorganization, indicating that ant trophic interactions are robust to tree species loss.