What it Means to be a Threatened Species

Tigers are currently grouped into six extant subspecies on the basis of distinctive molecular markers: Amur Tiger, Northern Indochinese Tiger, Malayan Tiger, Sumatran Tiger, Bengal Tiger, and the South China Tiger (possibly extinct). Three subspecies previously recognized on the basis of morphology are extinct: the Bali Tiger, Javan Tiger, and the Caspian Tiger. (Photograph by IUCN Photo Library/Steve Winter)

Most people know what it means to be a threatened species—it’s something that’s rare and may become extinct. What isn’t often explained is how we know something is threatened and who decides whether a species is threatened or not.

Read almost any article about species in peril and there will be some reference to the level of threat faced by that species. Words like Vulnerable, Endangered, and Critically Endangered are usually mentioned without any real explanation of where these categories come from or how they are determined. Part of the reason for this is that it’s just easier to take the author’s word for it and move on. However, in science, the author’s word is not good enough—statements must be supported by data and methods and these must be presented for open (and often scathing) review by other scientists. This process of peer-review is the foundation of all credible scientific work and species science is no exception.

When determining the threat status of a species, the International Union for Conservation of Nature (IUCN) has developed a set of peer-reviewed categories and criteria based on the best available science. When a species is assessed it is assigned one of nine categories: Not Evaluated, Data Deficient, Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild, or Extinct. The category to which a species is assigned is based on a rigorous evaluation of a set of four broad criteria. These include an estimate of current population size, geographic range, reductions in population size, and the probability of extinction in the wild.

Scientists throughout the world collect data on the population size of species in as many places as possible to get an idea of how many individuals there are in nature and how far they roam. Often, despite their herculean attempts, researchers are unable to count every single living individual. In reality, species are tricky—most of them are quite small and make a habit of not being conspicuous.

What scientists must then rely on are proven statistical methods of counting a sample of individuals to come up with estimates of total population size. These estimates are then combined with where a species lives—its geographic extent or range. The likelihood of extinction in the wild is what the estimated population size and ranges are compared against. Scientists must base their assessments of extinction probability on life histories, habitat requirements, and threats facing a species, each of which must be appropriate, documented, and defendable. Following this process, an assessed species will be assigned to one of the IUCN Red List categories.

Bunaea alcinoe_NE_Craig Beatty
This Common Emperor Moth (Bunaea alcinoe) has not yet been evaluated by the IUCN Red List. It’s worth noting that the Common Skate (Dipturus batis) is a Critically Endangered Species, despite its name. (Photograph by Craig Beatty)

Based on these criteria more than 21,000 species of the 71,576 species on The IUCN Red List are threatened with extinction. For instance, it is estimated that fewer than 400 Ethiopian Wolves (Canis simensis) remain in the wild. They are restricted to seven isolated mountain enclaves in the highlands of Ethiopia at altitudes above 3500 meters. Their habitat is being encroached upon by agriculture and canine distemper disease, and climate change may continue to increase the threats to this species.

Ethiopian Wolf
Photograph by Brent Huffman/UltimateUngulate

The IUCN Red List currently records 799 Extinct species and without appropriate conservation action this number will increase. Sixty-one species are listed as Extinct in the Wild (existing only in captive populations) and 4,286 are listed as Critically Endangered. Each one of these species is the tip of an evolutionary branch, millions of years in the making. Unfortunately, an unknown number of species have been pushed to extinction before they were described by science or assessed by the IUCN Red List.

People and organizations all over the world make it their life’s work to conserve species, biodiversity and habitats. We feel a ground-swell of support as more people around the world are realizing just how dependent we are on the biodiversity that surrounds us.  The interactions among species and between nature and people cascade through our lives in ways that we are sincerely starting to recognize on a global level. The IUCN Red List is an indispensable asset for building awareness and informing communities, conservationists, and governments in making the best decisions about the future of life on this planet, including our own.

The International Union for Conservation of Nature is the world’s oldest and largest global environmental organization made up of more than 1,000 organizations, as well as 10,000 individual scientists and experts working on conservation around the globe. Perhaps we are best known for the IUCN Red List of Threatened Species, which is the global standard for species science and conservation information and the connection to human livelihoods and is celebrating 50 years of conservation action in 2014.
  • Devon Michael

    I found the article to be very relative as i myself have never asked how a species is catogorized. I have a few questions. what is done when a species is declared extinct in the wild? At which status does a species have to be at for it to cause concern? and are these evaluations on going?

    • Thanks for reading, Devon! The IUCN Red List is designed as a guide for conservation action. Often when a species is declared extinct in the wild there is a rush to preserve the individuals remaining in captivity. There have been successful examples of species that have been successfully reintroduced after being declared extinct in the wild (the Black-footed ferret and several species of Polynesian tree snail come to mind) and in South Africa, Cycads (the most threatened group of species assessed) there are intensive conservation efforts to reintroduce species. However, this is not always the case and there are plenty of species that have been classified as Extinct in the Wild and then unfortunately the species becomes extinct in captivity (for example, Lonesome George – the last Pinta Island Tortoise died in 2012).

      The concern caused by a species’ threat category is dependent on many interacting factors, including who you’d like to be concerned. The IUCN Red List monitors the conservation status of species and concern should start with species that are Near Threatened, Not Evaluated, or Data Deficient. The level of concern should rise with the increasing threat categories. However, concern is based on the recognition that a species is disappearing or has the potential to disappear and more than counting individuals, this requires the conservation of habitat. The IUCN Red List provides the information necessary for decision-makers to make informed conservation choices and the level of concern they feel is directly dependent on the people they represent.

      As much as possible, evaluations are ongoing. Our goal is to increase the number of species assessed to 160,000 by 2020 and there are several groups of species that have been assessed in the past, but their assessments require updating. With the support of our partner organizations, volunteers, governments, and people like you we can continue assessments and make the IUCN Red List a more complete Barometer of Life.

  • Benjamin Gosselin

    I’m afraid the government of Canada doesn’t fully understand the concept, especially concerning the Humpback whale…

  • Jerome Girard

    A very revealing and scary article. My question is, what sanctioned are instituted against group who continue to contribute towards these threats? Is it that they especially governments, do not understand the long term implications? Is the global fight being taken to our schools? If so, to waht Extent?

  • sarah emery

    This is world wide problem even in USA. Example of a disease crossing to another species—like HIV did to humans who ate bush meat long before we knew about HIV. How this one made to the Americas is the question I have.Was it thru someone having an exotic pet, from animal acquired from a zoo. Watched a documentary last night. Had never heard of this. So another threat to endangered species like Siberia tigers.

  • Dana J

    Is there a specific author for this article so I can cite it?

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