The rules make it easier to remove an animal from the endangered species list. It will also weaken protection for the animals considered "threatened species," a categorization that means a species is at risk to be endangered. For the first time, economic assessments will be allowed when determining the animals included on the list. It's likely that the new rules will open the door to development, mining and drilling in habitats of protected species. The Endangered Species Act is considered the cornerstone of American conservation. It's credited with being instrumental in saving the bald eagle, the American alligator and the grizzly bear from extinction. Environmental organizations have denounced the changes.