The survival of ecosystems (plant and animal communities and their physical surroundings) such as forests, coral reefs, or wetlands depends on their biodiversity, or variety of plants, animals, and habitats, as well as the many interactions among these species. The removal or disappearance species may irreversibly damage the ecosystem and put it into a decline. For example, the undersea kelp forests of the northern Pacific rim are some of the richest marine habitats known-they are the home or breeding ground of many species of fish and other wildlife. When the sea otter population off the western coast of Canada and the United States was hunted down in the 19th and early 20th centuries, invertebrates such as the sea urchin were left without a major predator. The population of sea urchins increased dramatically and rapidly consumed the kelp and other
seaweed, turning the ecosystem into a barren undersea desert. Conservation efforts throughout the latter half of the 20th century, such as the U.S. Marine Mammal Protection Act (1972), allowed for the protection and reintroduction of the sea otter to these ecosystems and the kelp forests have since then improved.
The loss of biodiversity is irreversible, and has a serious impact on the ability of remaining species, including humans, to survive. Humans depend on species diversity and healthy ecosystems to provide food, clean air and water, and fertile soil for agriculture. In addition, we benefit greatly from the many medicines and other products that biodiversity provides. As many as 40 percent of our modern pharmaceutical medicines are derived from plants or animals. A small plant from Madagascar, the rosy periwinkle, produces substances that are effective in fighting two deadly cancers, Hodgkin's disease and leukemia. Yet the forest habitat of the rosy periwinkle is rapidly disappearing to supply firewood and farmland for the impoverished people of Madagascar, and most of the endemic species (species that live nowhere else) there are endangered.
Decline - How it affects you