chapter  3
16 Pages

Applying time to event methods to assess pollutant effects on populations

Ecological risk assessment aims to estimate the probability of some adverse consequence of contaminant exposure. Although ecological risk assessments involving endangered or exceptionally charismatic species do focus on individuals, effects most frequently of concern are those on populations. This being the case, it is incongruent that most information applied to estimating

ecological risk comes from studies designed to assess effects on individuals. Fortunately, extrapolation from such information to population consequences can be improved by applying time to event methods in ecotoxicity testing and field surveys. Survival methods, including life table analysis, produce meaningful information (e.g., intrinsic rates of increase) amenable to projecting consequences such as local population extinction. The higher statistical power of the time to event approach relative to the conventional concentration-effect approach allows predictions incorporating important demographic and genetic covariates. Proportional hazard models allow easy estimation of relative fitness for genotypes that can be used in selection models to predict changes in tolerance or allele frequency through time. Our intent is to describe these advantages of time to event methods for predicting effects on population demographics and genetics.