Human activities threaten the existence of plants and animals worldwide. Overhunting, deforestation, and encroachment on natural habitats all pose threats. The current rate of species extinction is between one hundred and one thousand times greater than the expected natural rate. A 2008 International Union for Conservation of Nature (IUCN) report stated that nearly one third of amphibians, one in eight birds, and one in four mammals are threatened with extinction. Ecosystem functioning depends on the existence and health of numerous interacting species. These interactions make human life possible. Habitat loss, illegal killing, and human encroachment threaten big cat populations. Conservation efforts have helped sustain populations of other endangered species like the humpback whale, whooping crane, and grizzly bear. Scientific research and concentrated breeding programs can help preserve species.