Redhorse suckers (Moxostoma) in the Grand River, Ontario: how do six ecologically similar species coexist?
The syntopic existence of five or six species of redhorse suckers in small sections of some Ontario rivers leads us to question how fishes with very similar ecology and life history are able to coexist. My thesis adopts a resource partitioning hypothesis to examine this phenomenon. I investigated body shape variation among all six redhorse species found in Ontario with the hypothesis that the different redhorse species are adapted to varying degrees to living in fast currents. I found significant differences among the six species of redhorse found in Ontario. I also compared the utility of traditional morphometric techniques with newer geometric morphometric methods (Thin Plate Spline Analysis--TPS) for the purpose of size removal in morphometric data. I found TPS results to be easier to interpret due to the generation of visual deformation grids and more consistent in identifying the specific location of shape variation. I also examined home range and spatial distribution patterns in three of the six species, to test the prediction that different redhorse species prefer different habitats. I did not find any significant differences in home range size among species however, I did find significant differences in current velocity and depth of fish locations among species. In addition, I found low spatial overlap between the three redhorse species examined. Based on the findings of these two chapters, I have concluded that resource partitioning is occurring among redhorse suckers in the Grand River and that it may be an important mechanism in facilitating their coexistence.