An understanding of food web structure is critical for the management of fisheries and biodiversity in aquatic systems.  Trophic pathways determine the productivity of fish species, community susceptibility to perturbations such as invasive species introductions, and the transfer and biomagnification of contaminants.  In the Laurentian Great Lakes trophic structure has been altered continuously over the past century due to fishing pressure, fish stocking, and invasive species.  In Lake Malawi and the other African Great Lakes, complex trophic structure allows for the coexistence of many fish species with minimal competition.  Our lab uses several tools, with an emphasis on stable isotopes of carbon and nitrogen, to determine trophic linkages and food web structure in large lakes.  Specific questions currently being addressed in Lake Michigan include: 1) How is the food web adapting to the loss of pelagic resources and the increase in nearshore energy?  2) How does food web structure vary spatially?  3) What are the trophic linkages through which the Clostridium botulinum toxin is transferred to fish and birds?