2020 vision : meeting the fish wildlife conservation challenges of the 21st century : proceedings of a symposium held at the 53rd Midwest Fish and Wildlife Conference--Des Moines, Iowa, December 3, 1991 / Tony J. Peterle, editor ; David J. Case, symposium chair ; sponsored by the North Central Section of the Wildlife Society and co-sponsored by the Organization of Wildlife Planners [and] North Cen...