Is the per capita rate of increase a good measure of population-level effects in ecotoxicology?

In this paper we consider the relationships between effects of toxicants on population growth rate (r) and the individual-level traits (survival and r eproduction) contributing to it by examining population dynamics theory and by reviewing the experimental work that has been carried out in this conte xt. There was no consistent pattern in terms of which individual-level trai ts were most or least sensitive to toxicant exposure, and it is therefore i mpractical to select traits for ecotoxicological testing on this basis. Alt hough percent changes in several of the individual-level traits showed sign ificant overall correlations with percent changes in r, changes in any sing le trait could explain no more than about one-half of the percent change in r. Our conclusion is that r is a better measure of responses to toxicants than are individual-level effects, because it integrates potentially comple x interactions among life-history traits and provides a more relevant measu re of ecological impact.