Knowledge of how environments and phenotypes interact with density in determining demographic rates is valuable in population ecology, because this identifies how the strength and shape of density dependence may differ among and within populations. Anothe r issue relating to population regulation that requires further studies is one of scale. In most organisms, density varies at different spatial scales, as does density dependence, and it is rarely known which scale of variation is most important in influe ncing overall productivity. Due to the complex nature of population regulation, considering both the spatiotemporal scale of density dependence, and interactions between density, phenotype and environment, a population modelling approach that is linked to the underlying mechanisms is required to understand spatiotemporal population dynamics. In the present project, Atlantic salmon will be used as a model organism to address these issues, using a pluralistic approach combining experimental studies with ind ividual/behavioural based population modelling.