Je. Kammenga et al., STRESS-INDUCED FITNESS REDUCTION IS NOT DETERMINED BY THE MOST SENSITIVE LIFE-CYCLE TRAIT, Functional ecology, 10(1), 1996, pp. 106-111
1. It is widely assumed that stressors such as toxicants affect organi
sms by impairment of those life-cycle variables that are most sensitiv
e to these toxicants. We tested this premise by contrasting a fitness
assessment with the most sensitive life-cycle variable approach using
cadmium and the nematode Plectus acuminatus as a case study. 2. Based
on complete life-cycle experiments, a deterministic model was construc
ted relating changes in juvenile and adult variables, including a Weib
ull survival distribution, to fitness, which was defined as the intrin
sic rate of population increase. 3. Based on a sensitivity analysis of
the model it was indicated that impairment of the most sensitive trai
t, the reproductive period which was reduced by 45%, did not have any
effect on fitness. However, a prolongation by cadmium of the juvenile
period by 7.5%, the least sensitive trait, resulted in a fitness decre
ase of 5%. 4. Application of this approach to the evaluation of critic
al effect levels for cadmium implies that a hazard assessment based on
the most sensitive life-cycle trait leads to erroneous predictions of
the biological impact that toxicants cause.