What Are Endangered Species?
The International Union for the Conservation of Nature is the world's leading surveyor of ecosystems, primarily flora and fauna; they annually compile scientific research and data, and publish it under various formats — most notably is their Red List of Categories and Criteria (illustrated in the chart below). The following list briefly outlines the IUCN Red List, including the seven levels of species endangerment.
These are common organisms — they represent the plants and animals that one might encounter every day. Presently, the species of least concern have stable populations, and are therefore in no immediate threat of decline (e.g. rats, pigeons, grass, maple trees, dogs, cats, humans).
Near threatened species might appear as abundantly or commonly as those of least concern, and so do not yet qualify for formal conservation protection. However, due to present and/ or surrounding circumstances, it seems certain that these organisms will become threatened at some point in the future.
An organism classifies as vulnerable when its population and negative habitat trends obviate a high risk of extinction. It is important to note that all estimates are relative to the surveyed species, so population numbers are just one factor in the overall analysis process. But in general, vulnerable species have a 10% probability of going extinct in the wild, within the next 100 years (and therefore require wildlife protection measures).
Endangered species face an even greater risk of extinction, than do vulnerable species. The probability data extends out to 100 years (maximum), but usually does not project beyond 20 years (or else five generations), during which time the organism faces a 20% probability of extinction.
Species facing a 50% chance of extinction within the next 10 years (or else three generations), represent the critically endangered category. These organisms are extremely few in number (usually less than 250 individuals), and populations are typically fractured, or inbred. In terms of conservation, critically endangered species receive the highest priority of protection, and usually require some form of human intervention (like captive breeding programs), in order to avoid extinction.
EXTINCT IN WILD
Declaring an organism extinct in the wild denotes species which have neither been seen nor surveyed in the wild, for quite some time (the time depends on the organism, as well as following up all reports of sightings). The only known populations of these extremely rare creatures either live in captivity, or else well outside of native habitat/ ranges (thus, these species are too difficult for researchers to adequately locate and quantify).
An organism is deemed extinct when no reasonable doubt remains of its permanent and absolute elimination from the ecosystem. Their absence is final—after eons of evolution and survival, this living creature has no more exact, genetic relatives left on earth—its existence during this geological period is over, and forever.