Using aggregation methods to assess toxicant effects on population dynamics in spatial systems

Risk assessment in ecotoxicology currently requires extrapolating laboratory results (e.g., bioassays) to populations living. in fragmented heterogeneous environments. To date, metapopulation modeling has been able to contribute little to pollutant management for environment preservation and conservation biology. This situation results from the more general issue of the spatial dimension of ecological systems. We have used aggregation methods to' build an ecotoxicological population model for a river network. Our model described a brown trout population exposed to chronic cadmium pollution. Age structure, spatial distribution, and demographic and migration processes were taken into account to estimate population response to different scenarios of pollutant discharge. For this purpose a multi-region Leslie matrix model was coupled with dose-response curves. Endpoints were features of population dynamics: the asymptotic population growth rate, the stable age structure, and the reproductive values. Thus, different pollution scenarios were compared in terms of subsequent reduction in the population growth rate or in terms of stable age-structure changes.