My research focuses on the structure and composition of ecological communities in aquatic ecosystems. The major emphasis is comparing fish communities in lakes and streams to determine the relative importance of environmental factors in determining the species composition. My work compares the fish community composition of lakes from several regions of Ontario, but concentrates on lakes in south-central Ontario. The communities are determined primarily by constraints imposed by lake morphology (e.g. depth, thermal and oxygen conditions), secondarily by water chemistry (e.g. acidification) and biotic interactions (i.e. predation). Species within these lakes experience period extinctions due to environmental conditions. Currently I am studying the colonization and extinction of fish species within lakes and their connecting waterways to quantify the role of these factors in determining fish community structure. The patterns in community composition of benthic invertebrates across lakes show a significant association with the fish communities, but the inverts appear to be influenced more by lake water chemistry rather than morphological conditions. Additional invertebrate work has been directed at crayfish ecology, including the population structure, habitat association and spatial movements of crayfish in lakes. Given the large number of species found in communities and the diverse environmental variables associated with them, I work with aspects of statistical ecology. In particular much of this is directed at assessing and developing methods of multivariate statistical analysis. Such analyses permit the summary of community patterns and their relationship with the physical and chemical environment.