Any organism including plants or animals can become endangered. Organisms are classified by the International Union for Conservation of Nature (IUCN) into the following categories.
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Extinct (EX) – beyond a reasonable doubt that the species is no longer extant.
Extinct in the wild (EW) – survives only in captivity, cultivation and/or outside the native range, as presumed after exhaustive surveys.
Critically endangered (CR) – in an extremely critical state.
Endangered (EN) – very high risk of extinction in the wild, meets any of criteria A to E for Endangered.
Vulnerable (VU) – meets one of the 5 red list criteria and thus considered to be at high risk of unnatural (human-caused) extinction without further human intervention.
Near threatened (NT) – close to being at high risk of extinction in the near future.
Least concern (LC) – unlikely to become extinct in the near future.
The following is a simplified look at the 5 criteria used to classify organisms by the IUCN.
A) Reduction in population
B) Geographic range
C) Population estimated to number fewer than 2,500 mature individuals and in decline
D) Population size estimated to number fewer than 250 mature individuals.
E) Quantitative analysis showing the probability of extinction in the wild is at least 20% within 20 years or five generations
Check out https://www.iucnredlist.org
to look at the population status of thousands of plants and animals.
Some organisms are inherently more at risk for extinction than others. One of the traits that distinguish species is the difference in reproductive rate. R-strategists like mice reproduce very quickly and would have the potential for a quick population rebound. K-strategists like elephants spend a lot of time and energy on each offspring and would take a long time to recover a population loss.
In addition to their reproductive rate, the ability of an organism to adapt to environmental change has a huge impact on their survival rate. Specialist species like orangutans tend to fit into a very specific niche. A specialist organism might eat only one thing or live in a limited habitat. These organisms have a very hard time surviving environmental change or pressures. On the other hand, generalist organisms like pigeons adapt well to a variety of different climates, food, and environmental challenges.
Countries have developed a variety of strategies in order to address the decline in species. The most vital of which is the implementation of legislation to protect habitats. The Endangered Species Act of 1973 was introduced with the goal of protecting endangered and threatened species by preserving habitats from development. This Act is often the center of much debate as it prevents the growth or development of cities and industries.
Possibly one of the most important tools to conserve species is education. There has been a large movement worldwide to educate the public on how human actions are causing a massive decline in species. By educating people about the potential extinction of large charismatic animals like the polar bear and tiger, the public is more willing to take steps necessary to save species.
Many zoos and aquariums are used as education centers while at the same time using the animals in captive breeding programs to rebuild populations. The Smithsonian National Zoo and the San Diego Zoo have been instrumental in establishing populations in critically endangered species like the black-footed ferret, red panda, and clouded leopard.