stage may be caused by differences in the food
source. However, in our experiment the Collembola
were maintained on the same diet. Likely, the
observed changes in
15
N fractionation were due to a
reduced metabolism in older Collembola. The 12
weeks old individuals stopped to lay eggs and
moulting was infrequent. Fractionation in
Cdid
not change significantly with age. Again this contradicts
findings from Scheu and Folger (2004) where
fractionation was generally more pronounced in
adult (2.7%)thaninjuvenile(0.91%) Heteromurus
nitidus (Collembola).
13