Species of animals or organisms are considered extinct when there are no more of them alive. Animals that are classified as "endangered" are at risk of becoming extinct.
Some animals are considered extinct in the wild. This means that the only surviving members of the species live in captivity, like in a zoo.
Animals become extinct for a variety of reasons. Today many animals are endangered or have become extinct due to the influence of humans. Some of the ways that animals become extinct are described below.
Natural Forces
Over the course of history many species have become extinct. This is part of the natural process. Species may become extinct because of changes in climate (i.e. the ice age), competition with other species, a reduced food supply, or combinations of all of these.
Most natural extinctions are isolated events that happen over a fairly long period of time. Some, however, are major events that can cause mass extinctions and happen quickly. Perhaps the most famous of these was the extinction of the dinosaurs, which may have been due to a large meteorite striking the Earth.
Human Interaction
Today many conservationists are concerned with human interaction causing species to become extinct. This is because human interaction has increased the rate of extinctions beyond what normally should occur in nature. More extinctions reduces the planet's biodiversity and can have adverse affects for all life on Earth.
Hunting
Many species have been hunted to extinction or to the point where they are critically endangered. One example of this is the American Bison. There were millions of bison in the Great Plains of North America until the arrival of the Europeans. Hunting was so intense that only a few hundred were left by the time the animals became protected. Fortunately, they have survived on farms and ranches and are no longer endangered.
Species that live only on islands can also be easily hunted to extinction. Even the arrival of a small tribe can quickly eliminate an island species.
The florida panther is endangered Source: USFWS
Furs, Skins, Feathers, Horns
Besides food, animals are often hunted for specific body parts like their fur, feathers, or horns. Sometimes these animals are the top predators and, therefore, do not have a large population to begin with. These species can be quickly hunted to extinction.
In Africa, the elephant was heavily hunted for its prized ivory horns. The population went from many millions to a few hundred thousand. Today the elephant is protected, but the population continues to drop in some areas due to poachers.
Another example is the tiger in China. The tiger was nearly hunted to extinction for both its valuable fur as well as its bones, which were traditionally used for medicine. Today it remains classified as an endangered species.
Loss of Habitat
One of the main threats to animals today is loss of habitat. This comes from the expansion of humans, especially from agriculture. As vast areas of land are cultivated to grow food, natural habitats are destroyed. This can destroy many of the cycles of life necessary for organisms to survive and for biomes to thrive.
Pollution
Pollution from humans can kill off a species as well. This is especially true in fresh water biomes such as rivers and lakes. Sewage and run-off from industrial plants can poison the water. When one species is affected, other species can die off as well causing a chain reaction as the balance of the ecosystem is destroyed.
Introduced Species
When a new species of plant or animal is brought into an ecosystem it can become invasive, quickly taking over and killing off other species. It may also destroy an important part of the food chain causing many other species to suffer.
