A threatened species is a form of the organism that is on the verge of extinction (National Geographic). Species may become extinct due to one of two factors: lack of genetic diversity or loss of habitat. Different groups use different standards to determine whether a species is endangered. Among the prominent and well-known organizations are the United States Fish and Wildlife Service (USFWS) and the International Union for Conservation of Nature (IUCN) (IUCN). The International Union for the Conservation of Nature’s Red List of Threatened Species aims to provide a status index for all species and organisms worldwide (IUCN).
The purpose of this paper is to discuss endangered species, with regards to how species are endangered, how they have categorized, and the concerns regarding endangered species.
How Species are Endangered
Each and every organism needs a place to live, but a habitat is not limited to just a habitat. It includes where the organism gets food, raises its offspring and allows the next generation to take over (Bove). Often there are few warning signs that a given species could become extinct. Species like the Atlantic salmon may be at risk due to their economic importance (Bove). Additionally, species with lengthy gestational periods or produce few offspring at each birth are more likely to be more readily endangered. Finally, some species have weak genetic makeup and hence are at high risk of extinction with each generation. There are two main ways through which species are endangered, these are, loss of habitat and loss of genetic variation.

Loss of Habitat

Natural Causes

Loss of habitat may occur naturally resulting in endangerment without any human interference. Among the many reasons for animal endangerment, habitat destruction is the number one cause (Bove). For example, around 65 million years back, dinosaurs lost their habitat due to the hot climate of the period that changed so fast probably due to asteroid striking the earth (National Geographic). Since the amount of heat and light reaching the earth surface was reduced, the earth became cooler and hence the dinosaurs could not adapt to the cooler habitat thus they became endangered then extinct. Organisms can also face the risk of extinction which is a natural part of evolution. Other natural factors like competition, sudden climatic changes, overspecialization and catastrophes such as volcanic eruptions and earthquakes may lead to the decline of many species (Bove).

Human Activities

Human activity can also result in loss of habitat. Activities like development for industry, agriculture and housing reduce the habitat of the native species and this can take place in various ways. Development can clear habitat and native species directly, like where developers clear vast areas by cutting down all trees and removing all vegetation. For example, developers have cleared thousands of acres of South America’s Amazon Forest to set up ranches, logging areas and for urban use (National Geographic). Physical encroachment through human development into the animal habitat bring about pollutions to the natural landscape through chemicals and petroleum products. Such activities may lead to the outright death of some species while other may be pushed into other areas that they may not be able to find food and shelter. Eventually, the suffering of one animal due to human activities affects other species in the food web and hence more species die.

Apart from directly endangering species, development can also threaten species indirectly. Some species like fig trees of a forest provide habitat for other species like the birds. When such trees are threatened through destruction, species that depend on them also become endangered. Other plants like fungi and vines live in the forests on the trees and therefore when trees are destroyed it means that they have less room for reproduction and life.


Loss of habitat may also occur where development in a species range, that is, the geographical area within which a species is found. Several living organisms have a range of area within which they are found. For example, North America’s mountain lion has a range of about 386 square miles or 1000 square kilometers, of which for them to live successfully, on has to patrol the entire range (National Geographic). The 20th century saw the rapid growth of cities such as Los Angeles and California and as they expanded into the wilderness, the mountain lions’ habitat got reduced. However, the mountain lions are not endangered since some parts of the mountain ranges remain undeveloped.

Human-Species Encounters

Loss of habitat can also result in increased encounters between man and the wild species. When development gets humans deeper into the species range, they may be more exposed to the wild species. It may also mean that the poisonous plants grow closer to homes and other developments and wild animals are seen more often. Since human have moved into their species range, their interaction with humans may be fatal as they are patrolling within their territory. Some of the species that have been brought close contact with humans due to loss of their habitat to homes and farms include mountain lions, alligators and the polar bears (National Geographic). Native species may become endangered as a result of people killing the wild though chemicals or hunting, accidents like collisions.

Loss of Genetic Variation

Genetic variation is the diversity found in a given species (National Geographic). It allows organisms to adapt to various environmental changes and hence the greater the population of a species, the greater the genetic variation. Loss of genetic variation can occur due to four main reasons including human activities, inbreeding, natural causes and monoculture.

Human Activities

Human activities such as overfishing and overhunting can contribute to loss of genetic variation leading to population decline of the species. Reduction of the population of the given species means that would be less breeding pairs available. A breeding pair comprises two mature members of the species that have no close relation and can bring forth a healthy offspring (National Geographic). Less breeding pairs translate to less genetic variation.


Inbreeding refers to reproduction between close family members. It may contribute to a loss of genetic variation. When there is inbreeding among a given species then there is little genetic variation since no new information is added to the particular species. Therefore it means that for inbred groups there are a higher risk of disease and consequently death since they lack the variation to develop the resistance. It is unlikely for offspring of inbred species to live to maturity.

Natural Causes

Loss of genetic variation can also take place naturally. For instance, cheetahs of Africa and Asia are a threatened species since they naturally have little genetic variation (National Geographic). According to biologists, the small genetic differences in cheetahs is a result of long periods of inbreeding in the last ice age. Therefore, few of them survive to maturity since they are not able to adapt to environmental changes like other species. Unlike other members of the big cat’s family like lions that can be bred in captivity, cheetahs are more unmanageable to breed in captivity.


Like animal species, plant species too can be subject to loss of genetic variation, for instance through monoculture. Monoculture is the agricultural practice of growing one crop (National Geographic). For example, most of the potatoes that consumed are from a single species, which means they lack genetic variation. Since the crops have little genetic variation, farmers are often forced to use pesticides and fertilizers to keep them healthy. Most of the time plant breeders have to collect the genes of the native plants to cultivate crops that are resistant to both drought and pests.

Red List of Threatened Species

IUCN maintains a “Red List of Threatened Species” which defines the species’ threat of extinction and the causes (National Geographic). The list has nine groups with each group representing different threat levels. The groups include extinct, extinct in the wild, critically endangered, endangered, vulnerable, near threatened, least concern, data deficient and not evaluated (IUCN). The first two categories have the species that are not threatened by extinction. “Least Concern” represents the lowest level of conservation. It means the given species in that category has an abundant population that is widespread. Human beings fall in this category, along with most of the domestic animals like cats and dogs. Even wild animals like birds and insects such as houseflies fall in the same category. However, for the sake of this paper, the focus remains on endangered and the critically endangered species.

Endangered Species

Before categorizing an organism as either endangered or critically endangered, five key factors are considered, these are, population size, geographic range, population decline rate, population restrictions, and the probability of extinction (Buechley and Sekercioglu).

Population size

The number of individual members of a species’ group is very significant in determining whether the species is endangered or not. A species is categorized as endangered if there are less than 2500 existing mature individuals (National Geographic).

Geographic Range

A species is classified as endangered if its spatial extent of occurrence is less than 500 square kilometers or 1930 square miles (National Geographic). Similarly, if the species occupancy area is less than 500 square kilometers or 1930 square miles, then it is categorized as an endangered species (National Geographic).

Population Decline Rate

If the population of a given species has reduced by 50-70 percent, then it is categorized as endangered (National Geographic). This reduction is determined over a duration of 10 years or three generations of the species, whichever is longer. Even though most of the time the cause of population decline is not known, sometimes it is known and this gives another criterion for another form of categorization. Where the population has declined by at least 70 percent and the cause for the decline is known then the species is classified as endangered. When a species’ population reduces by at least 50 percent and the cause of is unknown then the species is categorized as endangered (IUCN).

Probability of Extinction

It is approximated that in the wild, the probability of extinction is five generations or at a minimum of 20 percent within a period of 20 years, whichever is longer (National Geographic).

Population Restrictions

Where population restriction is considered then a species whose population is restricted to less than 250 mature individuals is regarded as endangered. In cases where the population of the given specie is this low then the area it occupies is not taken into consideration.

Examples of Endangered Species

Tahiti Reed-warbler

Tahiti Reed-warbler, referred to scientifically as Acrocephalus caffer is a songbird found only on the Pacific island of Tahiti. Its low population earns it a position as one of the endangered species (Earth’s Endangered Creatures). Since it is only occurring in one island means that its area of occupancy and extent of occurrence are very small. Human activities in the island has made the species endangered. The bird lives only on the bamboo forests of the island. Other species invade the forest and since the birds live almost exclusively in the bamboo forests, their population has kept on declining.

Siberian Sturgeon

Siberian sturgeon whose scientific name is Acipenser baerii is a large fish found across the Serbia region of Russia in lakes and rivers (Earth’s Endangered Creatures). Being a member of the benthic species, siberian sturgeons live at the bottom of the water bodies. Since the population of this species has declined by about 50-80 percent in the last 60 years, it is classified as an endangered species (National Geographic). Some of the causes of the population decline include; poaching, dam construction, overfishing and pollution brought about by mining activities.


Ebony which is scientifically referred to as Diospyros crassiflora is found around central Africa in the rain forests of Gabon, Congo and Cameroon. Its probability of extinction in the wild set at a minimum of 20 percent within five generations and thus, it is categorized as an endangered species (Earth’s Endangered Creatures). It produces very high-quality hardwood that is dark and heavy. It’s good quality has led to overharvesting for making furniture and sculptures. Most of the ebony harvested is used in making some parts of musical instruments like pianos (National Geographic).

Critically Endangered Species

Population Size

If the total number of a given species is less than 250 mature individuals then it is classified as critically endangered (National Geographic). Additionally, if the population of the mature individuals of a species decline by 25 percent in either one generation or three years (whichever is lower) then it is classified as critically endangered (National Geographic).

Geographic Range

A species occurs in an extent less than 39 square miles then it is classified as critically endangered. Similarly, if the area a species occupies is approximated to be less than 4 square miles then it is classified as endangered (National Geographic).

Population Reduction Rate

If the population of a given species has fallen by 80-90 percent over a period of 10 years, then the species is classified as critically endangered. Where the population is at a minimum of 90 percent and the cause is known then the species is categorized as critically endangered. In case the decline is at a minimum of 80 percent but the cause is unknown, then it is categorized as critically endangered (IUCN).

Probability of Extinction

If the probability of extinction of a given species in the wild is at least 50 percent within a period of 10 years or three generations (any that is longer), then is classified as critically endangered (National Geographic).

Population Restrictions

When the population of a particular species is fewer than 50 mature individuals then it is classified as critically endangered. In a situation that the population is this low then the area occupied is not taken into consideration (IUCN).

Examples of Critically Endangered Species

White Ferula Mushroom

White ferula mushroom scientifically referred to as Pleurotus nebrodensis is only found in Sicily island of Italy in the Mediterenean Sea (Earth’s Endangered Creatures). It belongs to the fungus family and is critically endangered because it occurs in less than 39 square miles. The mushroom is harvested for food and sale and thus overharvesting is the main threat to the loss of its habitat.

Bolivian Chinchilla Rat

Bolivian chinchilla rat is scientifically referred to as Abrocoma bolivensis is a rodent that only occurs in a small part of Santa Cruz region in Bolivia (Earth’s Endangered Creatures). Its extent of occurrence is less than 39 square miles and thus classified as critically endangered. Human activities through the clearing of forests for pasture results in loss of the cloud forest which is the rat’s habitat (Earth’s Endangered Creatures).

Transcaucasian Racerunner

The Transcaucasia racerunner, scientifically known as Eremias pleskei is a lizard that is critically endangered species found in Armenian plateau in Armenia, Azerbaijan, Iran and Turkey. It is estimated that in the last 10 years, the population of the lizard had fallen by over 80 percent (National Geographic). The huge population decline is attributed to salination due to fertilizers applied in agricultural development. Since the lizards cannot adapt to the increased salt in their habitat, their population is declining. Additionally, the lizard is losing habitat from human habit of dumping trash on the lizard’s area of occupancy.

Works Cited

Bove, Jennifer. Why are Animals Endangered. 15 November 2016. .

Buechley, Evan and Cagan H Sekercioglu. “Endangered Species.” Grzimek. Grzimek’s Animal Life Encyclopedia. Gale, 2013. 159-175.

Earth’s Endangered Creatures. n.d. Web. 29 March 2017. .

IUCN. IUCN, International Union for Conservation of Nature. n.d. Web. 29 March 2017.

National Geographic. Endangered Species. 2017. .

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