Endangered species: Any species of fish, plant life, or wildlife that is in danger of extinction throughout all or a significant part of its range, other than a species of insecta determined by the Department, or the Secretary, of the United States Department of the Interior to constitute a pest whose protection under this part would present an overwhelming and overriding risk to humans.
Threatened species: Any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.
Special Concern: While not afforded legal protection under the Act, many of these species are of concern because of declining or relict populations in the state. Should these species continue to decline, they would be recommended for Threatened or Endangered status. Protection of Special Concern species now, before they reach dangerously low population levels, would prevent the need to list them in the future by maintaining adequate numbers of self-sustaining populations within Michigan. Some other potentially rare species are listed as of Special Concern pending more precise information on their status in the state; when such information becomes available, they could be moved to Threatened or Endangered status or deleted from the list.
Extirpated: Any species which can no longer be found in the state of Michigan, but which can be found elsewhere in the world.
Extinct: Any species which can no longer be found anywhere in the world.
From the Michigan DNR's website at http://www.michigan.gov/dnr/0,1607,7-153-10370_12141_12168-30439--,00.html