My research aims primarily at improving our understanding of spatial and temporal variation in the structure (abundance, size distribution) of populations and communities. I generally rely on quantitative tools, such as Bayesian statistics and dynamic models, to analyse how structure and dynamics relate to environmental features or biotic interactions, mostly in field settings. My work in Canada and in the neotropics has encompassed a variety of lacustrine and riverine organisms, including microscopic algae, planktonic and benthic invertebrates, and fish. Even though fundamental questions motivate most of this research, results of our studies (e.g. measures of growth, mortality, and production; density estimates; movement and migratory behaviour; effects of nutrient enhancement; marking techniques) often have relevance for management of species of high economic, subsistence, or conservation value, such as Atlantic salmon and brook charr, and neotropical floodplain fishes.