Endangered Species | National Geographic Society (2023)

An endangered species is a type of organism that is threatened by extinction. Species become endangered for two main reasons: loss of habitat and loss of genetic variation.

Loss of Habitat

A loss of

habitat

can happen naturally. Dinosaurs, for instance, lost their

habitat

about 65 million years ago. The hot, dry climate of the Cretaceous period changed very quickly, most likely because of an asteroid striking the Earth. The impact of the

asteroid

forced debris into the atmosphere, reducing the amount of heat and light that reached Earth’s surface. The

dinosaurs

were unable to adapt to this new, cooler

habitat

.

Dinosaurs

became endangered, then extinct.

Human activity can also contribute to a loss of

habitat

. Development for housing, industry, and agriculture reduces the

habitat

of native organisms. This can happen in a number of different ways.

Development

can eliminate

habitat

and native species directly. In the Amazon rain forest of South America, developers have cleared hundreds of thousands of acres. To “clear” a piece of land is to remove all trees and vegetation from it. The Amazon rain forest is cleared for cattle ranches, logging, and urban use.

Development

can also endanger species indirectly. Some species, such as fig trees of the rain forest, may provide

habitat

for other species. As trees are destroyed, species that depend on that tree

habitat

may also become endangered. Tree crowns provide

habitat

in the canopy, or top layer, of a rainforest. Plants such as vines, fungi such as mushrooms, and insects such as butterflies live in the rain forest

canopy

. So do hundreds of species of tropical birds and mammals such as monkeys. As trees are cut down, this

habitat

is lost. Species have less room to live and reproduce.

Loss of

habitat

may happen as

development

takes place in a species range. Many animals have a range of hundreds of square kilometers. The mountain lion of North America, for instance, has a range of up to 1,000 square kilometers (386 square miles). To successfully live and

reproduce

, a single

mountain lion

patrols this much territory. Urban areas, such as Los Angeles, California, and Vancouver, British Columbia, Canada, grew rapidly during the 20th century. As these areas expanded into the wilderness, the

mountain lion

’s

habitat

became smaller. That means the

habitat

can support fewer

mountain lions

. Because enormous parts of the Sierra Nevada, Rocky, and Cascade mountain ranges remain undeveloped, however,

mountain lions

are not endangered.

Loss of

habitat

can also lead to increased encounters between wild species and people. As

development

brings people deeper into a

species range

, they may have more exposure to wild species. Poisonous plants and

fungi

may grow closer to homes and schools. Wild animals are also spotted more frequently. These animals are simply

patrolling

their range, but interaction with people can be deadly. Polar bears,

mountain lions

, and alligators are all predators brought into close contact with people as they lose their

habitat

to homes, farms, and businesses. As people kill these wild animals, through pesticides, accidents such as collisions with cars, or hunting, native species may become endangered.

Loss of Genetic Variation

Genetic variation

is the diversity found within a species. It’s why human beings may have blond, red, brown, or black hair.

Genetic variation

allows species to

adapt

to changes in the environment. Usually, the greater the population of a species, the greater its

genetic variation

.

Inbreeding is reproduction with close family members. Groups of species that have a tendency to

inbreed

usually have little

genetic variation

, because no new genetic information is introduced to the group. 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 offspring of inbred 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,

cheetahs

went through a long period of

inbreeding

. As a result, there are very few genetic differences between

cheetahs

. They cannot

adapt

to changes in the environment as quickly as other animals, and fewer

cheetahs

survive to maturity.

Cheetahs

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

. Overhunting and overfishing have

reduced

the populations of many animals.

Reduced

population means 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

shrinks.

Monoculture, the agricultural method of growing a single crop, can also

reduce

genetic variation

. Modern agribusiness relies on

monocultures

. Almost all potatoes cultivated, sold, and consumed, for instance, are from a single species, the Russet Burbank. Potatoes, native to the Andes Mountains of South America, have dozens of natural varieties. The

genetic variation

of wild potatoes allows them to

adapt

to climate change and disease. For

Russet Bur

banks

, however,

farmers

must use fertilizers and

pesticides

to ensure healthy

crops

because the plant has almost no

genetic variation

.

Plant breeders often go back to wild varieties to collect genes that will help

cultivated

plants resist pests and drought, and

adapt

to

climate

change

. However,

climate

change

is also threatening wild varieties. That means domesticated plants may lose an important source of traits that help them overcome new threats.

The Red List

The International Union for Conservation of Nature (IUCN) keeps a “

Red List

of

Threatened Species

.” The

Red List

defines the severity and specific causes of a species’ threat of

extinction

. The

Red List

has seven levels of

conservation

: least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and

extinct

. Each category represents a different threat level.

Species that are not threatened by

extinction

are placed within the first two categories—

least concern

and near-threatened. Those that are most threatened are placed within the next three categories, known as the threatened categories—vulnerable, endangered, and

critically endangered

. Those species that are

extinct

in some form are placed within 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 can be of

least concern

in one area and endangered in another. The gray whale, for instance, has a healthy population in the eastern Pacific Ocean, along the coast of North and South America. The population in the western Pacific, however, is

critically endangered

.

Least Concern

Least concern

is the lowest level of conservation. A species of

least concern

is one that has a widespread and abundant population. Human beings are a species of

least concern

, along with most domestic animals, such as dogs and cats. Many wild animals, such as pigeons and houseflies, are also classified as

least concern

.

Near Threatened

A near

threatened species

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

Many species of violets, native to

tropical

jungles in South America and Africa, are

near threatened

, for instance. They have healthy populations, but their rain forest

habitat

is disappearing at a fast pace. People are cutting down huge areas of rain forest for

development

and timber. Many

violet

species are likely to become threatened.

Vulnerable Species

The definitions of the three

threatened categories

(vulnerable, endangered, and

critically endangered

) are based on five criteria: population reduction rate, geographic range, population size, population restrictions, and probability of extinction.

Threatened categories

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

1) Population reduction rate
A species is classified as vulnerable if its population has declined 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 time it is able to

reproduce

. Mice are able to

reproduce

when they are about one month old. Mouse populations are mostly tracked over 10-year periods. An elephant's

generation

lasts about 15 years. So, elephant populations are measured over 45-year periods.

A species is vulnerable if its population has

declined

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

declined

at least 30 percent and the cause of the

decline

is not known. A new, unknown virus, for example, could kill hundreds or even thousands of individuals before being identified.

2) Geographic range
A species is vulnerable if its “extent of occurrence” is estimated to be less than 20,000 square kilometers (7,722 square miles). An

extent of occurrence

is the smallest area that could contain all sites of a species’ population. If all members of a species could survive in a single area, the size of that area is the species’

extent of occurrence

.

A species is also classified as vulnerable if its “area of occupancy” is estimated to be less than 2,000 square kilometers (772 square miles). An

area of occupancy

is where a specific population of that species resides. This area is often a breeding or nesting site in a

species range

.

3) Population size
Species with fewer 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.

4) Population restrictions
Population restriction is a combination of population and

area of occupancy

. A species is vulnerable if it is restricted to less than 1,000

mature

individuals or an

area of occupancy

of less than 20 square kilometers (8 square miles).

5)

Probability of

extinction

in the wild is at least 10 percent within 100 years.
Biologists

, anthropologists, meteorologists, and other scientists have developed complex ways to determine a species’

probability of

extinction

. These formulas calculate the chances a species can survive, without human protection, in the wild.

Vulnerable Species: Ethiopian Banana Frog
The Ethiopian banana frog (Afrixalus enseticola) is a small frog native to high-altitude areas of southern Ethiopia. It is a

vulnerable species

because its

area of occupancy

is less than 2,000 square kilometers (772 square miles). The extent and quality of its forest

habitat

are in

decline

. Threats to this

habitat

include forest clearance, mostly for housing and

agriculture

.

Vulnerable Species: Snaggletooth Shark
The snaggletooth shark (Hemipristis elongatus) is found in the

tropical

,

coastal

waters of the Indian and Pacific Oceans. Its

area of occupancy

is

enormous

, from southeast Africa to the Philippines, and from China to Australia.

However, the snaggletooth shark is a

vulnerable species

because of a severe

population reduction rate

. Its population has fallen more than 10 percent over 10 years. The number of sharks is declining due to fisheries, especially in the Java Sea and Gulf of Thailand. The snaggletooth shark’s flesh, fins, and liver are considered high-quality foods. They are sold in commercial fish markets, as well as restaurants.

Vulnerable Species: Galapagos Kelp
Galapagos kelp (Eisenia galapagensis) is a type of seaweed only found near the Galapagos Islands in the Pacific Ocean. Galapagos

kelp

is classified as vulnerable because its population has

declined

more than 10 percent over 10 years.

Climate

change

is the leading cause of

decline

among Galapagos

kelp

. El Nino, the natural weather pattern that brings unusually warm water to the Galapagos, is the leading agent of

climate

change

in this area. Galapagos

kelp

is a cold-water species and does not

adapt

quickly to changes in water temperature.

Endangered Species

1) Population reduction rate
A species is classified as endangered when its population has declined between 50 and 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 declined at least 70 percent and the cause of the decline is known. A species is also classified as endangered when its population has declined at least 50 percent and the cause of the decline is not known.

2) Geographic range
An endangered species’ extent of occurrence is less than 5,000 square kilometers (1,930 square miles). An endangered species’ area of occupancy is less than 500 square kilometers (193 square miles).

3) Population size
A species is classified as endangered when there are fewer than 2,500 mature individuals. When a species population declines by at least 20 percent within five years or two generations, it is also classified as endangered.

4) Population restrictions
A species is classified as endangered when its population is restricted to less than 250 mature individuals. When a species’ population is this low, its area of occupancy is not considered.

5) Probability of extinction in the wild is at least 20 percent within 20 years or five generations, whichever is longer.

Endangered Species: Siberian Sturgeon
The Siberian sturgeon (Acipenser baerii) is a large fish found in rivers and lakes throughout the Siberian region of Russia. The Siberian

sturgeon

is a benthic species.

Benthic

species live at the bottom of a body of water.

The Siberian

sturgeon

is an

endangered species

because its total population has

declined

between 50 and 80 percent during the past 60 years (three

generations

of

sturgeon

).

Overfishing

, poaching, and dam construction have caused this

decline

. Pollution from mining activities has also contributed to abnormalities in the

sturgeon

’s reproductive system.

Endangered Species: Tahiti Reed-warbler
The Tahiti reed-warbler (Acrocephalus caffer) is a songbird found on the Pacific

island

of Tahiti. It is an

endangered species

because it has a very small population. The bird is only found on a single

island

, meaning both its

extent of occurrence

and

area of occupancy

are very small.

The Tahiti reed-

warbler

is also endangered because of human activity. The

tropical

weed Miconia is a non-native species that has taken over much of Tahiti’s native

vegetation

. The reed-

warbler

lives almost exclusively in Tahiti’s bamboo forests. The bird nests in

bamboo

and feeds on flowers and insects that live there. As

development

and invasive species such as Miconia destroy the bamboo forests, the population of Tahiti reed-warblers continues to shrink.

Endangered Species: Ebony
Ebony (Diospyros crassiflora) is a tree native to the rain forests of central Africa, including Congo, Cameroon, and Gabon.

Ebony

is an

endangered species

because many

biologists

calculate

its

probability of

extinction

in the wild is at least 20 percent within five

generations

.

Ebony

is threatened due to overharvesting.

Ebony

trees produce a very heavy, dark wood. When polished,

ebony

can be mistaken for black marble or other stone. For centuries,

ebony

trees have been harvested for furniture and sculptural uses such as chess pieces. Most

ebony

, however, is harvested to make musical instruments such as piano keys and the fingerboards of stringed instruments.

Critically Endangered Species

1) Population reduction rate
A critically endangered species’ population has declined between 80 and 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 declined at least 90 percent and the cause of the decline is known. A species is also classified as endangered when its population has declined at least 80 percent and the cause of the decline is not known.

2) Geographic range
A critically endangered species’ extent of occurrence is less than 100 square kilometers (39 square miles). A critically endangered species’ area of occupancy is estimated to be less than 10 square kilometers (4 square miles).

3) 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 declines by at least 25 percent within three years or one generation, whichever is longer.

4) Population restrictions
A species is classified as critically endangered when its population is restricted to less than 50 mature individuals. When a species’ population is this low, its area of occupancy is not considered.

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

Critically Endangered Species: Bolivian Chinchilla Rat
The Bolivian chinchilla rat (Abrocoma boliviensis) is a rodent found in a small section of the Santa Cruz region of Bolivia. It is

critically endangered

because its

extent of occurrence

is less than 100 square kilometers (39 square miles).

The major threat to this species is loss of its cloud forest

habitat

. People are clearing forests to create cattle pastures.

Critically Endangered Species: Transcaucasian Racerunner
The Transcaucasian racerunner (Eremias pleskei) is a lizard found on the Armenian Plateau, located in Armenia, Azerbaijan, Iran, and Turkey. The Transcaucasian

racerunner

is a

critically endangered

species because of a huge population

decline

, estimated at more than 80 percent during the past 10 years.

Threats to this species include the salination, or increased saltiness, of soil.

Fertilizers

used for agricultural

development

seep into the

soil

, increasing its saltiness.

Racerunners

live in and among the rocks and

soil

, and cannot

adapt

to the increased salt in their food and shelter. The

racerunner

is also losing

habitat

as people create trash dumps on their

area of occupancy

.

Critically Endangered Species: White Ferula Mushroom
The white ferula mushroom (Pleurotus nebrodensis) is a

critically endangered

species of fungus. The mushroom is

critically endangered

because its

extent of occurrence

is less than 100 square kilometers (39 square miles). It is only found in the northern part of the Italian

island

of Sicily, in the Mediterranean Sea.

The leading threats to white ferula mushrooms are loss of

habitat

and

overharvesting

. White ferula mushrooms are a gourmet food item.

Farmers

and amateur mushroom hunters harvest the fungus for food and profit. The mushrooms can be sold for up to $100 per kilogram (2.2 pounds).

Extinct In The Wild

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

Extinct in the Wild: Scimitar-horned Oryx
The scimitar-horned oryx (Oryx dammah) is a species of antelope with long horns. Its range extends across northern Africa. The

scimitar

-horned

oryx

is listed as

extinct

in the wild

because the last confirmed sighting of one was in 1988.

Overhunting

and

habitat

loss, including competition with domestic livestock, are the main reasons for the

extinction

of the

oryx

’s wild population.

Captive herds are now kept in protected areas of Tunisia, Senegal, and Morocco.

Scimitar

-horned

oryxes

are also found in many zoos.

Extinct in the Wild: Black Soft-shell Turtle
The black soft-shell turtle (Nilssonia nigricans) is a freshwater

turtle

that exists only in one man-made pond, at the Baizid Bostami Shrine near Chittagong,

Bangladesh

. The 150 to 300

turtles

that live at the pond rely entirely on humans for food. Until 2000, black soft-shell

turtles

lived throughout the wetlands of the Brahmaputra River, feeding mostly on freshwater fish.

Unlike other animals that are

extinct

in the wild

, black soft-shell

turtles

are not found in many

zoos

. The

shrine

’s caretakers do not allow anyone, including scientists, to take the

turtles

. The reptiles are considered to be the descendants of people who were miraculously turned into

turtles

by a saint during the 13th century.

Extinct in the Wild: Mt. Kaala Cyanea
The Mt. Kaala cyanea (Cyanea superba) is a large, flowering tree native to the

island

of Oahu, in the U.S. state of Hawaii. The Mt. Kaala

cyanea

has large, broad leaves and fleshy fruit. The tree is

extinct

in the wild

largely because of

invasive species

. Non-native plants crowded the

cyanea

out of its

habitat

, and non-native animals such as pigs, rats, and slugs ate its fruit more quickly than it could

reproduce

.

Mt. Kaala

cyanea

trees survive in

tropical

nurseries and botanical gardens. Many botanists and

conservationists

look forward to establishing a new population in the wild.

Extinct

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

Extinct: Cuban Macaw
The Cuban macaw (Ara tricolor) was a

tropical

parrot native to Cuba and a small Cu

ban

island

, Isla de la Juventud. Hunting and collecting the birds for

pets

led to the bird’s

extinction

. The last specimen of the Cu

ban

macaw

was collected in 1864.

Extinct: Ridley’s Stick Insect
Ridley’s stick insect (Pseudobactricia ridleyi) was native to the tropical jungle of the island of Singapore. This insect, whose long, segmented body resembled a tree limb, is only known through a single specimen, collected more than 100 years ago. During the 20th century, Singapore experienced rapid development. Almost the entire jungle was cleared, depriving the insect of its habitat.

Extinct: Sri Lankan Legume Tree
The Sri Lankan legume tree (Crudia zeylanica), native only to the island of Sri Lanka in the Indian Ocean, was a giant species of legume. Peas and peanuts are smaller types of legumes.

Habitat loss from development in the 20th century is the main reason the tree went extinct in the wild. A single specimen survived at the Royal Botanical Garden in Peradeniya, Sri Lanka, until 1990, when that, too, was lost.

Endangered Species and People

When a species is classified as endangered, governments and international organizations can work to protect it. Laws may limit hunting and destruction of the species’

habitat

. Individuals and organizations that break these laws may face huge

fines

. Because of such actions, many species have recovered from their endangered status.

The brown pelican was taken off the

endangered species

list in 2009, for instance. This seabird is native to the

coasts

of North America and South America, as well as the

islands

of the Caribbean Sea. It is the state bird of the U.S. 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. Young chicks were reared in hatching sites, then released into the wild. Human access to

nesting sites

was

severely

restricted. The

pesticide

DDT, which

damaged

the eggs of the brown

pelican

, was

banned

. During the 1980s, the number of brown

pelicans

soared. In 1988, the IUCN “delisted” the brown

pelican

. The bird, whose population is now in the hundreds of thousands, is now in the category of

least concern

.

Fast Fact

Convention on Biological Diversity
The Convention on Biological Diversity is an international treaty to sustain and protect the diversity of life on Earth. This includes conservation, sustainability, and sharing the benefits of genetic research and resources. The Convention on Biological Diversity has adopted the IUCN Red List of endangered species in order to monitor and research species' population and habitats.

Three nations have not ratified the Convention on Biological Diversity: Andorra, the Holy See (Vatican), and the United States.

Fast Fact

Lonesome George
Until 2012, Lonesome George was the most endangered species on the planet. He was the only living species of Pinta Island tortoise known to exist. The Pinta Island tortoise was only found on Pinta, one of the Galapagos Islands. The Charles Darwin Research Station, a scientific facility in the Galapagos, offered a $10,000 reward to any zoo or individual for locating a single Pinta Island tortoise female. On June 25, 2012, Lonesome George died, leaving one more extinct species in the world.

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