Animals in danger of extinction are all those that are threatened with disappearing.

So few of the endangered animals remain that they could soon disappear entirely. Although some plants and animals have always evolved more successfully than others, human activity is changing the world in such a way that many animals and plants are much more exposed than they would otherwise be.

Species are endangered for two main reasons: loss of habitat and the loss of genetic variation.

Loss of habitat

Loss of habitat can occur naturally. Dinosaurs, for example, lost their habitat around 65 million years ago. The hot and dry climate of Cretaceous It changed very quickly, most likely due to an asteroid hitting Earth. The impact of the asteroid forced debris into the atmosphere, reducing the amount of heat and light reaching the Earth's surface. The dinosaurs were unable to adapt to this new, cooler habitat, causing them to become "endangered" and then go extinct.

Human activity can also contribute to habitat loss. The development of land for housing, industries and agriculture reduces the habitat of native organisms considerably. This can happen in a number of different ways.

Development can directly eliminate native species and habitat. In the Amazon rainforest of South America, thousands upon thousands of hectares of land, trees and vegetation have been removed. The Amazon rainforest is cut down for cattle ranches, raw materials, and urban use.

Development can also indirectly endanger species. Some species, such as the fig trees of the rainforest, can provide habitat for other species. As trees are destroyed, the species that depend on that tree habitat may also become endangered. Tree canopies provide habitat in the canopy, or top layer, of a rainforest. Plants like vines, fungi, and insects like butterflies live in the canopy of the rainforest. So do hundreds of species of tropical birds and mammals like monkeys. As trees are cut down, this habitat is lost. Species have less space to live and reproduce.

Habitat loss can occur as development takes place in a species' range. Many animals have a range of hundreds of square kilometers. The North American cougar, for example, has a range of up to 1.000 square kilometers. To live and reproduce successfully, a single cougar patrols this territory. Urban areas, such as Los Angeles, California, and Vancouver, British Columbia, Canada, grew rapidly during the XNUMXth century. As these areas expanded into the wild, the habitat of the cougar was reduced. That means the habitat can support fewer cougars. However, because huge parts of the mountain ranges the pumas are not currently in danger.

Loss of habitat can also lead to increased encounters between wildlife and people. As human development moves us further into the range of species, we cause them to be more exposed. These animals are in their range, but interaction with humans can be deadly. Polar bears, cougars, and alligators are predators that come into close contact with people when they lose their habitat in favor of their homes, farms, and businesses. As people kill these wild animals, through pesticides, accidents such as car collisions, or hunting, native species may become endangered.

Loss of genetic variation

Genetic variation is the diversity found within a species. That is why human beings can have blonde, red, brown or black hair. The genetic variation allows species to adapt to changes in the environment. Typically, the larger the population of a species, the greater its genetic variation.

Inbreeding is reproduction with close family members. Groups of species prone to inbreeding usually have little genetic variation, as no new genetic information is introduced into the group. The disease is much more common, and much more deadly, among inbred groups. Inbred species do not have the genetic variation to develop resistance to the disease. For this reason, fewer descendants of consanguineous groups survive to maturity.

Loss of genetic variation can occur naturally. Cheetahs are a threatened species native to Africa and Asia. These big cats have very little genetic variation. Biologists say that during the last ice age, they went through a long period of inbreeding. As a result, there are very few genetic differences between them. They cannot adapt to changes in the environment as quickly as other animals, and fewer cheetahs survive to maturity. They are also much more difficult to breed in captivity than other big cats, such as lions.

Human activity can also lead to a loss of genetic variation. The hunting and overfishing they have reduced the populations of many animals. The reduction in population means that there are fewer breeding pairs. A breeding pair is made up of two mature members of the species that are not closely related and can produce healthy offspring. With fewer breeding pairs, genetic variation is reduced.

Monoculture, the agricultural method of growing a single crop, can also reduce genetic variation. Modern agribusiness depends on monocultures.

Breeders often turn to wild varieties to collect genes that will help cultivated plants resist pests and drought, and adapt to climate change. However, climate change also threatens wild varieties. This means that domesticated plants can lose an important source of traits that help them overcome new threats.

The Red List

International Union for the Conservation of Nature (IUCN) maintains a "Red List of Threatened Species". The Red List defines the severity and specific causes of the threat of extinction of a species. The Red List has seven levels of conservation and each category represents a different level of threat:

  • Not Evaluated (NE).
  • Insufficient Data (DD).
  • Least Concern (LC).
  • Near threatened (NT).
  • Vulnerable (VU).
  • Endangered (EN).
  • Critically Endangered (CR).
  • Extinct in the wild (EW).
  • Extinguished (EX).

Species that are not threatened by extinction fall into the first two categories: least concern and near threatened. Those most threatened fall into the following three categories, known as threat categories: vulnerable, endangered, and critically endangered. Those species that are extinct in some way fall into the last two categories (Extinct in the wild and extinct).

Classifying a species as endangered has to do with its range and habitat, as well as its actual population. For this reason, a species may be of least concern in one area and endangered in another. The gray whale, for example, has a healthy population in the eastern Pacific Ocean, along the coast of North and South America. However, the western Pacific population is critically endangered.

Least Concern (LC)

The least concern is the lowest level of conservation. A species of least concern is one that has a large and abundant population. Humans are a species of least concern, along with most domestic animals, such as dogs and cats. Many wild animals, such as pigeons and house flies, are also classified as the least of concern.

Near Threatened (NT)

A near threatened species is one that is likely to qualify for a threat category in the near future.

Many species of violets, native to the rainforests of South America and Africa, are near threatened, for example. They have healthy populations, but their rainforest habitat is disappearing at an accelerating rate. People are cutting down large areas of rainforest for development and timber. Many species of violets are likely to be threatened.

Vulnerable species

The definitions of the three threat categories (vulnerable (VU), endangered (EN) y critically endangered (CR)) are based on five criteria: population reduction rate, geographic distribution area, population size, population restrictions, and probability of extinction.

Threatened categories have different thresholds for these criteria. As the population and range of the species decrease, the species becomes more threatened.

Population reduction rate

One species is classified as vulnerable if your population has decreased between 30 and 50 percent. This decline is measured over 10 years or three generations of the species, whichever is longer. A generation is the period of time between the birth of an animal and the moment it is able to reproduce. Mice are capable of reproducing when they are about a month old. Mouse populations are mostly tracked over 10-year periods. The generation of an elephant lasts about 15 years. Therefore, elephant populations are measured in 45-year periods.

A species is vulnerable if its population has decreased by at least 50 percent and the cause of the decline is known. Habitat loss is the leading known cause of population decline.

A species is also classified as vulnerable if its population has decreased by at least 30 percent and the cause of the decline is unknown. A new and unknown virus, for example, could kill hundreds or even thousands of people before being identified.

Geographic reach

A species is vulnerable if its "extent of occurrence" is estimated to be less than 20.000 square kilometers. An occurrence degree is the smallest area that could contain all the population sites of a species. If all members of a species could survive in a single area, the size of that area is the extent of the species' presence.

A species is also classified as vulnerable if its "area of ​​occupation" is estimated to be less than 2.000 square kilometers. An occupation area is where a specific population of that species resides. This area is often a breeding or nesting site in the range of a species.

Population size

Species with less than 10.000 mature individuals are vulnerable. The species is also vulnerable if that population declines by at least 10 percent within 10 years or three generations, whichever is longer.

Population restrictions

The population restriction is a combination of population and area of ​​occupation. A species is vulnerable if it is restricted to fewer than 1.000 mature individuals or an area of ​​occupation of less than 20 square kilometers.

Probability of extinction

The probability of extinction in the wild is at least 10% within 100 years. Biologists, anthropologists, meteorologists, and other scientists have developed complex ways to determine the probability of extinction of a species. These formulas calculate the chances that a species can survive, without human protection, in the wild.

Endangered species

As with vulnerable species, they are measured in the same way, but with a differentiated criterion, attentive to differences, and try not to confuse them.

Population reduction rate

A species is classified as endangered when its population has decreased by 50 to 70 percent. This decline is measured over 10 years or three generations of the species, whichever is longer.

A species is classified as endangered when its population has decreased by at least 70 percent and the cause of the decline is known. A species is also classified as endangered when its population has decreased by at least 50 percent and the cause of the decline is unknown.

Geographic reach

The extent of the presence of an endangered species is less than 5.000 square kilometers. The area of ​​occupation of an endangered species is less than 500 square kilometers.

Population size

A species is classified as endangered when there are fewer than 2.500 mature individuals. When the population of a species decreases by at least 20% within five years or two generations, it is also classified as endangered.

Population restrictions

A species is classified as endangered when its population is restricted to fewer than 250 mature individuals. When the population of a species is so low, its area of ​​occupation is not considered.

Probability of extinction

The probability of extinction in the wild is at least 20% within 20 years or five generations, whichever is longer.

Critically endangered species

Population reduction rate

The population of a critically endangered species has declined by 80 to 90 percent. This decline is measured over 10 years or three generations of the species, whichever is longer.

A species is classified as critically endangered when its population has decreased by at least 90 percent and the cause of the decline is known. A species is also classified as endangered when its population has decreased by at least 80 percent and the cause of the decline is unknown.

Geographic reach

The extent of the presence of a critically endangered species is less than 100 square kilometers. The area of ​​occupation of a critically endangered species is estimated to be less than 10 square kilometers.

Population size

A species is classified as critically endangered when there are fewer than 250 mature individuals. A species is also classified as critically endangered when the number of mature individuals decreases by at least 25 percent in three years or in one generation, whichever is longer.

Population restrictions

A species is classified as critically endangered when its population is restricted to fewer than 50 mature individuals. When the population of a species is so low, its area of ​​occupation is not considered.

Probability of extinction

The probability of extinction in the wild is at least 50 percent within 10 years or three generations, whichever is longer.

Extinct in the wild (EW)

A species becomes extinct in the wild when it only survives in cultivation (plants), in captivity (animals), or as a population that is outside its established range. A species can be listed as extinct in the wild only after years of studies that have failed to register an individual in its native or expected habitat.

Extinct (EX)

A species becomes extinct when there is no reasonable doubt that the last remaining individual of that species has died.

Endangered species and people

When a species is classified as endangered, governments and international organizations can work to protect it. Laws can limit hunting and habitat destruction for the species. Individuals and organizations that violate these laws can face huge fines. Due to these actions, many species have recovered from their endangered status.

For example, the brown pelican was removed from the endangered species list in 2009. This seabird is native to the coasts of North and South America, as well as the islands of the Caribbean Sea. It is the state bird of the US state of Louisiana. In 1970, the number of brown pelicans in the wild was estimated at 10.000. The bird was classified as vulnerable.

During the 1970s and 1980s, governments and conservation groups worked to help the brown pelican recover. The young chicks were raised in hatching places and then released into the wild. Human access to the nesting sites was severely restricted. The pesticide DDT, which damaged brown pelican eggs, was banned. During the 1980s, the number of brown pelicans soared. In 1988, the IUCN 'excluded' the brown pelican. The bird, now in the hundreds of thousands, is in the category of least concern.