Nonylphenol stimulates fecundity but not population growth rate (lambda) of Folsomia candida.

The toxicity of nonylphenol (NP) to springtails was pronounced at 40 mg/kg dry weight soil, at which no animals survived. Body length and fecundity were the individual life-history traits significantly stimulated by sublethal concentrations of NP during a 64-day experiment. However, the effects of NP on these traits did not result in a statistically significant increase in population growth rate (lambda). Decomposition analysis indicated that fecundity was the main contributor to the (non-significant) changes observed in lambda. However, since the elasticity of fecundity was very low, large changes in fecundity resulted in a minimal effect on lambda. Juvenile survival had the highest elasticity of all traits, but was not affected by NP, and therefore did not contribute to effects on lambda. This study confirms previous studies showing that effects of chemicals on individual life-history traits are attenuated at the population level and that lambda is an appropriate endpoint for ecotoxicological studies.

The influence of nonylphenol on life-history of the earthworm Dendrobaena octaedra Savigny: linking effects from the individual- to the population-level.

We conducted a study to look at the effects of nonylphenol (NP) on the life-history of the parthenogenetic earthworm, Dendrobaena octaedra. During a 196-day study, we observed that the growth rate of juveniles and the percentage of worms producing cocoons were the only traits significantly affected by NP, while the total number of cocoons produced was marginally affected. Despite some fairly large changes in the average values of individual life-history traits caused by NP, the effects were difficult to detect statistically due to large interindividual variability. A declining trend was observed for population growth rate (lambda) with increasing NP concentration, but the decline was not statistically significant. The percent reduction in lambda was less than the percent reduction in the most sensitive life-history trait (fecundity). An elasticity analysis showed that lambda was more sensitive to changes in survival than to changes in reproductive traits. However, neither juvenile nor adult survival were affected by NP, and decomposition analysis showed that the minor changes in lambda were mainly caused by effects of NP on time to first reproduction, time between reproduction events and fecundity. The present study suggests that extrapolation from laboratory studies to population effects in the field may be greatly enhanced by combining ecotoxicological and demographic methods.