D15 ARTICLE IN PRESS N varied between 2.4%, which assigns a shift in one trophic level, and 6.3%,suggesting a shift in two trophic levels. Starvation up to 4 weeks resulted in an increase in the total d15 N value from 2.8% to 4.0%. Different life stages significantly affected the isotope discrimination by Collembola with juveniles showing a stronger enrichment (D15 N ¼ 4.9%) compared to adults (D15N ¼ 3.5%). D13 C varied between 2.1% and 3.3% depending on the food quality, mainly due to compensational feeding on low quality diet. During starvation d13 C value decreased by 1.1%, whereas the life stage of Collembola had no significant effect on isotopic ratios