Influence of Ecosystem Gradients on Community Structure

Environmental conditions can structure communities by having an effect on population state variables including abundance and trophic position. Habitat suitability models created for fish populations are often used to predict these state variables under a range of environmental conditions. However, in lakes where there are two competing fish species like walleye and lake trout, there may be a range where both species have almost equal suitability. These competitive interactions may cause alternative stable states.  Similarly, environmental conditions can switch a system from being dominated by juveniles to being dominated by adults within the same population. Environmental and state variables were collected from Ontario lakes surveyed during the OMNR Broad Scale Monitoring program and stable isotope diet analysis was performed to determine the level of competition and trophic position of lake trout and walleye.  Preliminary results suggest that there may be alternative stable states between adult and juvenile stages over a range of lake size, and alternative stable states for lake trout and walleye over a range of water clarity. However, there is little evidence for alternative stable states in trophic position or abundance over lake size.