| River ecosystems in the United States have undergone numerous changes in the last century. In North Dakota and Minnesota, widespread modifications of prairie habitat due to agricultural practices have altered the hydrology of most river basins. This dissertation identifies the proximate mechanisms by which these landscape changes are passed to aquatic organisms inhabiting the Missouri River, Red River of the North, and Mississippi River basins. Specifically, I examine how environmental disturbance, parasites, and diet alter the life history traits of white suckers (Catostomus commersoni Lacepede).;Macroinvertebrate communities were predicted by land use in the riparian zone of each tributary, while fish communities were predicted at the watershed scale. In addition, white suckers practice a size selective foraging behavior (select larger prey) on taxa that are most available in that environment. An analysis of white suckers' growth and reproduction revealed a high amount of variability among and within river basins. Portions of this variation are related to differences in land use, diet, and density of parasites. Physiological mechanisms (e.g., immune function as quantified by heterophil/lymphocyte ratio) also varied among tributaries and differing infection rates. The results of this study reiterate the need for fisheries management and conservation to take a multidisciplinary approach, by combining epidemiology and immunology with the fields of physiology, genetics, and ecology, to provide a holistic approach to the management of marine and freshwater fishes. |
