Life history elasticity and the population-level effect of p-nonylphenol on Daphnia galeata

In order to evaluate population-level effects of p-nonylphenol on a cladoce ran zooplankton (Daphnia galeata), the chronic effects on survival and repr oduction were estimated with partial life table tests, which examined respo nses in life history characters until 3 weeks after birth. The observed res ponses in survival and reproduction were converted to reductions of the int rinsic rate of natural increase r. The population level EC50, which is defi ned as the exposure concentration that reduces r by 50%, was estimated as 1 6.1 mug l(-1) In order to examine the extent to which the population-level effect in terms of r is influenced by extra mortality in nature, which is i nduced by predation, starvation, etc., sensitivity (elasticity) measures of the intrinsic rate of natural increase to reductions in age-specific survi val and reproduction were calculated under hypothetical predation schemes. The sensitivities of the intrinsic rate to changes in survival and reproduc tion invariably decline rapidly after the onset of reproduction irrespectiv e of predation schemes. This implies that partial life cycle tests until 21 days after birth can provide reliable estimates of the population-level ef fects.