Stable isotopes: past and future in exposing secrets of ant nutrition (Hymenoptera: Formicidae)

Feldhaar, H.; Gebauer, G.; Blüthgen, N.

Abstract: Ants can utilize a large variety of food sources, and this ability contributes to their ecological and evolutionary success. Their broad dietary niche, however, in conjunction with their sociality, makes this group of animals notoriously difficult to study with respect to nutritional ecology. Natural-abundance-stable-isotope studies are a useful tool for assessing the trophic position of ants in food webs. In theory, they may also help to assess the relative contribution of food sources to their biomass, although such quantitative estimates have to be taken with caution. Consumers are typically enriched in 15N and sometimes 13C relative to their diet. The magnitude of enrichment may be influenced by feeding mode, diet quality and possibly nitrogen-recycling endosymbiotic bacteria. We provide an estimate of the enrichment of stable isotopes relative to a chemically defined diet for the ant Camponotus floridanus (Buckley, 1866) and show that their endosymbiotic bacteria do not significantly alter the enrichment process. The average enrichment of C. floridanus pupae to their diet was 3.0‰ for 15N and 1.1‰ for 13C. Stable isotopes have also been used successfully for studying nutrient fluxes utilizing compounds enriched in either 15N or 13C as tracers. Such studies can help to elucidate nutrient fluxes, for example within an ant colony or between ants and other organisms such as plants. They may also clarify whether certain compounds can be metabolized by ants at all. Here we present an overview of topics and questions that can be addressed using stable-isotope methods. We discuss experimental design, sampling methods and potential pitfalls when applying stable-isotope techniques. We point out fields of research in ant biology that can be explored more extensively with stable-isotope analyses.

Myrmecol. News 13: 3-13; printable