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.
Bạn đang xem: Endangered species
An endangered species is a type of organism that is threatened by extinction. Species become endangered for two main reasons: loss of habitat và loss of genetic variation.Loss of HabitatA 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 và light that reached Earth’s surface. The dinosaurs were unable to lớn adapt to this new, cooler habitat. Dinosaurs became endangered, then extinct.Human activity can also contribute khổng lồ a loss of habitat. Development for housing, industry, & agriculture reduces the habitat of native organisms. This can happen in a number of different ways.Development can eliminate habitat & native species directly. In the Amazon rain forest of South America, developers have cleared hundreds of thousands of acres. To lớn “clear” a piece of land is to lớn remove all trees và vegetation from it. The Amazon rain forest is cleared for cattle ranches, logging, & 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 đứng đầu layer, of a rainforest. Plants such as vines, fungi such as mushrooms, & insects such as butterflies live in the rain forest canopy. So bởi hundreds of species of tropical birds and mammals such as monkeys. As trees are cut down, this habitat is lost. Species have less room lớn live và 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 lớn 1,000 square kilometers (386 square miles). Khổng lồ successfully live & 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 tư vấn fewer mountain lions. Because enormous parts of the Sierra Nevada, Rocky, và Cascade mountain ranges remain undeveloped, however, mountain lions are not endangered.Loss of habitat can also lead to increased encounters between wild species & people. As development brings people deeper into a species range, they may have more exposure lớn wild species. Poisonous plants and fungi may grow closer khổng lồ homes & 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, và alligators are all predators brought into close tương tác with people as they thảm bại their habitat lớn homes, farms, & 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 VariationGenetic variation is the diversity found within a species. It’s why human beings may have blond, red, brown, or đen hair. Genetic variation allows species to lớn 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 khổng lồ inbreed usually have little genetic variation, because no new genetic information is introduced to lớn the group. Disease is much more common, và much more deadly, among inbred groups. Inbred species do not have the genetic variation lớn develop resistance to lớn the disease. For this reason, fewer offspring of inbred groups survive to lớn 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 khổng lồ changes in the environment as quickly as other animals, and fewer cheetahs survive to lớn 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 và 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 lớn the Andes Mountains of South America, have dozens of natural varieties. The genetic variation of wild potatoes allows them khổng lồ adapt to lớn climate change and disease. For Russet Burbanks, however, farmers must use fertilizers và pesticides to lớn 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 và drought, and adapt to climate change. However, climate change is also threatening wild varieties. That means domesticated plants may thất bại an important source of traits that help them overcome new threats.The Red ListThe International Union for Conservation of Nature (IUCN) keeps a “Red list of Threatened Species.” The Red danh mục defines the severity & 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, & critically endangered. Those species that are extinct in some khung are placed within the last two categories—extinct in the wild & extinct.Classifying a species as endangered has to bởi vì with its range and habitat, as well as its actual population. For this reason, a species can be of least concern in one area & 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 ConcernLeast concern is the lowest màn chơi 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 & houseflies, are also classified as least concern.Near ThreatenedA near threatened species is one that is likely khổng lồ qualify for a threatened category in the near future.Many species of violets, native to lớn 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 và timber. Many violet species are likely to lớn become threatened.Vulnerable SpeciesThe definitions of the three threatened categories (vulnerable, endangered, & 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 & range of the species decreases, the species becomes more threatened.1) Population reduction rateA species is classified as vulnerable if its population has declined between 30 & 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 & the time it is able to reproduce. Mice are able lớn 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 & 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 & 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 rangeA species is vulnerable if its “extent of occurrence” is estimated khổng lồ 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 kích thước of that area is the species’ extent of occurrence.A species is also classified as vulnerable if its “area of occupancy” is estimated khổng lồ 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 sizeSpecies 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 restrictionsPopulation restriction is a combination of population and area of occupancy. A species is vulnerable if it is restricted lớn 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 lớn 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 FrogThe 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 chất lượng of its forest habitat are in decline. Threats lớn this habitat include forest clearance, mostly for housing và agriculture.Vulnerable Species: Snaggletooth SharkThe 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 lớn the Philippines, và from đài loan trung quốc 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 lớn fisheries, especially in the Java Sea & Gulf of Thailand. The snaggletooth shark’s flesh, fins, và liver are considered high-quality foods. They are sold in commercial fish markets, as well as restaurants.Vulnerable Species: Galapagos KelpGalapagos 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 lớn the Galapagos, is the leading agent of climate change in this area. Galapagos kelp is a cold-water species & does not adapt quickly to changes in water temperature.
Endangered Species1) Population reduction rateA 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 và the cause of the decline is not known.2) Geographic rangeAn 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 sizeA 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 restrictionsA 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 đôi mươi percent within 20 years or five generations, whichever is longer.Endangered Species: Siberian SturgeonThe 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, và dam construction have caused this decline. Pollution from mining activities has also contributed to lớn abnormalities in the sturgeon’s reproductive system.Endangered Species: Tahiti Reed-warblerThe 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 & 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 và invasive species such as Miconia destroy the bamboo forests, the population of Tahiti reed-warblers continues lớn shrink.
Endangered Species: EbonyEbony (Diospyros crassiflora) is a tree native lớn the rain forests of central Africa, including Congo, Cameroon, và Gabon. Ebony is an endangered species because many biologists calculate its probability of extinction in the wild is at least đôi mươi percent within five generations.Ebony is threatened due khổng lồ 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 & sculptural uses such as chess pieces. Most ebony, however, is harvested khổng lồ make musical instruments such as piano keys và the fingerboards of stringed instruments.Critically Endangered Species1) Population reduction rateA critically endangered species’ population has declined between 80 và 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 và 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 rangeA critically endangered species’ extent of occurrence is less than 100 square kilometers (39 square miles). A critically endangered species’ area of occupancy is estimated khổng lồ be less than 10 square kilometers (4 square miles).
Critically Endangered Species: Transcaucasian RacerunnerThe Transcaucasian racerunner (Eremias pleskei) is a lizard found on the Armenian Plateau, located in Armenia, Azerbaijan, Iran, & 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 lớn 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 & soil, & cannot adapt to the increased salt in their food & shelter. The racerunner is also losing habitat as people create trash dumps on their area of occupancy.Critically Endangered Species: trắng Ferula MushroomThe 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 và overharvesting. White ferula mushrooms are a gourmet food item. Farmers và amateur mushroom hunters harvest the fungus for food và profit. The mushrooms can be sold for up to lớn $100 per kilogram (2.2 pounds).Extinct In The WildA 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 khổng lồ record an individual in its native or expected habitat.Extinct in the Wild: Scimitar-horned OryxThe 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 & 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, & Morocco. Scimitar-horned oryxes are also found in many zoos.Extinct in the Wild: black Soft-shell TurtleThe 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 lớn 300 turtles that live at the pond rely entirely on humans for food. Until 2000, đen 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, đen soft-shell turtles are not found in many zoos. The shrine’s caretakers vày not allow anyone, including scientists, to lớn take the turtles. The reptiles are considered to lớn be the descendants of people who were miraculously turned into turtles by a saint during the 13th century.
Extinct in the Wild: Mt. Kaala CyaneaThe Mt. Kaala cyanea (Cyanea superba) is a large, flowering tree native to lớn the island of Oahu, in the U.S. State of Hawaii. The Mt. Kaala cyanea has large, broad leaves và fleshy fruit. The tree is extinct in the wild largely because of invasive species. Non-native plants crowded the cyanea out of its habitat, và 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 & botanical gardens. Many botanists và conservationists look forward lớn establishing a new population in the wild.ExtinctA species is extinct when there is no reasonable doubt that the last remaining individual of that species has died.Extinct: Cuban MacawThe Cuban macaw (Ara tricolor) was a tropical parrot native lớn Cuba và a small Cuban island, Isla de la Juventud. Hunting & collecting the birds for pets led to lớn the bird’s extinction. The last specimen of the Cuban macaw was collected in 1864.Extinct: Ridley’s Stick InsectRidley’s stick insect (Pseudobactricia ridleyi) was native khổng lồ the tropical jungle of the island of Singapore. This insect, whose long, segmented body toàn thân 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 TreeThe Sri Lankan legume tree (Crudia zeylanica), native only to lớn the island of Sri Lanka in the Indian Ocean, was a giant species of legume. Peas và 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 & PeopleWhen a species is classified as endangered, governments và international organizations can work to protect it. Laws may limit hunting & 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 danh sách 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 và 1980s, governments và conservation groups worked lớn help the brown pelican recover. Young chicks were reared in hatching sites, then released into the wild. Human access lớn 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.
A century ago, a bird called the passenger pigeon lived in North America. There were so many passenger pigeons that people often saw great flocks of them flying overhead containing thousands, even millions, of birds. Today, there is not a single one left. What happened?
The passenger pigeon became extinct. All living passenger pigeons disappeared from the earth entirely. The passenger pigeon became extinct for two reasons. First, the forests where it lived were cut down to make way for farms and cities. Second, many pigeons were shot for thể thao and because they were good lớn eat. At that time, there were no hunting laws khổng lồ protect endangered species lượt thích there are now.
There are over 1,300 endangered or threatened species in the United States today. Endangered species are those plants & animals that have become so rare they are in danger of becoming extinct. Threatened species are plants và animals that are likely to become endangered within the foreseeable future throughout all or a significant portion of its range.
How Does Extinction Happen?
Species disappear because of changes to lớn the earth that are caused either by nature or by the actions of people. Sometimes a natural event, like a volcano erupting, can kill an entire species. Other times, extinction will happen slowly as nature changes our world. For example, after the Ice Ages, when the glaciers melted và the earth became warmer, many species died because they could not live in a warmer climate. Newer species that could survive in a warmer environment took their places.
People can also cause the extinction of plants & animals. The main reason that many species are endangered or threatened today is because people have
changed the homes or habitats upon which these species depend. A habitat includes not only the other plants & animals in an area, but all of the things needed for the species" survival -- from sunlight and wind lớn food & shelter. The United States has many habitats, from ocean beaches to mountain tops. Every species requires a certain habitat in order to live. A cactus, for example, needs the sunny, dry desert in order khổng lồ grow. A polar bear, on the other hand, would not live in a desert, because it could not find enough food và water.
Pollution can also affect wildlife và contribute lớn extinction. The Nashville crayfish is endangered mainly because the creek where it lives has been polluted by people.
Pesticides & other chemicals can poison plants & animals if they are not used correctly. The bald eagle is one bird that was harmed by pesticides. In the past, a pesticide called DDT was used by many farmers. Rains washed the pesticide into the lakes & streams where it poisoned fish. After eating the poisoned fish, the eagles would lay eggs with very thin shells. These eggs were usually crushed before they could hatch. Today, people are not allowed lớn use DDT, và this has contributed lớn the bald eagle being removed from the endangered and threatened species lists needed for the species" survival -- from sunlight & wind to food & shelter.
The United States has many habitats, from ocean beaches khổng lồ mountain tops. Every species requires a certain habitat in order to live. A cactus, for example, needs the sunny, dry desert in order to grow. A polar bear, on the other hand, would not live in a desert, because it could not find enough food & water.
People can also endanger plants & animals by moving, or introducing, new species into areas where they vì chưng not naturally live. Some of these species bởi so well in their new habitat that they endanger those species already living there, called the native species. These introduced species are called invasive species. For example, when some fish are introduced into a lake or stream, they may prey upon, or eat the food of the native fish. The native species may then have lớn find a new source of food or a new home, or face becoming endangered or extinct.
Another way that people harm animals & plants is by taking them from the wild. Some people might catch an insect like the Mission blue butterfly for a butterfly collection. Others might capture a wild animal for a pet, or pick a flower because it"s pretty. In addition, some people illegally hunt animals for food, skins, or fur. In the past, lots of American crocodiles were killed so that their skins could be made into shoes và other clothing. This crocodile is now an endangered species.
Why Protect Endangered và Threatened Species?
Can you imagine walking in the woods without hearing birds singing, or picture what a field would be like without wildflowers blooming? Our plants và wildlife
make the world a more interesting và beautiful place. More importantly, all living species, including people, depend on other species for survival. For example, if a fish such as the shortnose sturgeon becomes extinct, all of the species that rely on it will also suffer and may become threatened or endangered.
We all depend upon plants and wildlife. From studying them, we have learned new ways of growing food, making clothing, and building houses. Scientists have discovered how to use certain plants & animals as medicine. If we fail lớn protect threatened or endangered species, we will never know how they might have improved our lives.
Endangered và threatened species need our help. Government agencies, such as the U.S. Environmental Protection Agency, the U.S. Ddulichsenviet.comrtment of
Agriculture, the U.S. Fish & Wildlife Service, NOAA"s National Marine Fisheries Service, và the National Park Service, along with state fish và wildlife agencies and private groups are making information available so people can better protect endangered and threatened species and their habitats. You can liên hệ these agencies for information & join the challenge in helping to protect endangered and threatened species, and all wildlife, from extinction.