Single and mixed diets in Collembola: effects on reproduction and stable isotope fractionation

1. Reproduction of Heteromurus nitidus (Collembola) feeding on conidial fungi, ectomycorrhizal fungi and soil algae in single and mixed diets was investigated. Feeding on mixed diets generally increased Collembola reproduction even in combinations of fungi/algae of high food quality with those of low food quality, indicating that Collembola generally benefit from feeding on mixed diets. 2. The contribution of dietary species in mixed diets to Collembola nutrition was quantified using stable isotope methods. Incorporation of carbon from fungal/algal species into H. nitidus in mixed diets varied with food quality indicating that Collembola are able to adjust the proportion of food materials ingested to maximize fitness. 3. Fractionation of C-13 and N-15 in H. nitidus feeding on single and mixed diets varied between diets and differed between juveniles and adults. The trophic structure of fungal feeding soil invertebrates cannot be inferred in a straightforward way from variations in natural abundances of stable isotopes, rather, stable isotope signatures reflect feeding guilds.