1994-present: Professor
Department of Forestry, University of Illinois

1989-1996: Director
Center for Biodiversity, Illinois Natural History Survey

1986: Interim Chief
Illinois Natural History Survey

1983-present: Affiliate Professor
Department of Ecology, Ethology, and Evolution, University of Illinois

1983-present: Graduate Faculty Member
University of Illinois

1982-1983: Interim Head of Section
Section of Faunistic Surveys, Illinois Natural History Survey

1980-present: Professional Scientist
Illinois Natural History Survey

1977-1980: Associate Professional Scientist
Illinois Natural History Survey

1972-1977: Assistant Professional Scientist
Illinois Natural History Survey

1967-1972: Research Assistant
Illinois Natural History Survey

1966-1967: Teaching Assistant
University of Illinois

1965-1966: Research Assistant
Illinois State University