Nitrogen and carbon isotope ratios in termites: an indicator of trophic habit along the gradient from wood-feeding to soil-feeding

1. Nitrogen and carbon stable-isotope ratios (delta(15)N and delta(13)C) of body tissues, mound/nest materials and dietary substrates were determined in termite species with differing trophic habits, sampled from the Mbalmayo Forest Reserve, southern Cameroon. 2. delta(15)N of termite tissues was enriched gradually along a spectrum of species representing a trophic gradient from wood-to soil-feeding. Species that could be identified from their general biology and from gut content analysis as feeding on well-rotted wood or as wood/soil interface feeders showed delta(15)N intermediate between sound-wood-feeders and soil-feeders. It is proposed that delta(15)N is therefore a possible indicator of the functional position of species in the humification process. Differences in delta(13)C were also observed between wood-feeding and soil-feeding forms. 3. High values of delta(15)N in soil-feeding termites suggest that nitrogen fixation is of little importance in these species. 4. A wide range of isotope effects (the difference in isotope ratios between termites and their diet) was observed for both nitrogen (Delta delta(15)N = -1.6 to + 8.8 parts per thousand) and carbon (Delta delta(13)C = -2.2 to + 3.0 parts per thousand), which suggests a diversity of nutrient acquisition mechanisms within termites and diverse relationships between termites and their intestinal micro-organisms.