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Why Species Become Endangered

Level: Pre-Intermediate

Extinction

Humans are one of about 1.75 million identified species. Many scientists believe that millions more species inhabit our world yet remain unidentified. Some species have become extinct after less than half a million years, while other species have existed almost unchanged for many millions of years. Contrary to popular belief, extinction is a natural process. For hundreds of millions of years, extinction has been occurring naturally, as part of the evolutionary process. Some cases of extinction have been caused by natural disasters, such as volcanic eruptions. Others have been the result of environmental changes, such as shifts in climate. Sometimes extinction occurs on a very large scale, with hundreds or thousands of species becoming extinct over a relatively short period of time. An example of this is the dinosaurs and their contemporaries, victims of a mass extinction that took place at least 65 million years ago. Based on fossil record, the average rate of extinction has been one species out of every million per century. However, today experts predict that at least one of every four species may become extinct by 2050.

Endangered species

Most people have a general idea of what an endangered, threatened, or extinct species is, but biologists have rather precise definitions for each term. An endangered species is a population of organisms, which is either so few in number or threatened by changing environmental or predation parameters that it is at risk of becoming extinct. The species usually has a small population and needs protection in order to survive. The mountain gorilla, the Indian python, the lady slipper orchid, and thousands of other plant and animal species throughout the world are endangered.

Biologists use the word threatened to describe species that face serious problems, but whose populations are not in immediate danger of becoming extinct. Some examples of threatened species are the African elephant, the northern spotted owl, and the eastern indigo snake.

Extinct species no longer exist or live anywhere in the world. The dodo, the passenger pigeon, and the dinosaurs are examples of extinct species.

Many countries have laws offering special protection to these species or their habitats: for example, forbidding hunting, restricting land development or creating preserves. Only a few of the many endangered species actually make it to the lists and obtain legal protection. Many more species become extinct, or potentially will become extinct, without gaining public notice.

The greatest factor of concern is the rate at which species are becoming extinct within the last 150 years. While species have evolved and become extinct on a regular basis for the last several hundred million years, the number of species becoming extinct since the Industrial Revolution has no precedent in biological history. If this rate of extinction continues, or accelerates as now seems to be the case, the number of species becoming extinct in the next decade could number in the millions. While most people readily relate to endangerment of large mammals or birdlife, some of the greatest ecological issues are the threats to stability of whole ecosystems if key species vanish at any level of the food chain.



Though extinction can be a natural effect of the process of Natural Selection, the current extinction crisis is not related to that process. At the present, the Earth is at a peak of biodiversity and scientists contend that the Earth is undergoing the sixth extinction period. These periods have occurred before without human intervention; however the current extinction period is unique. Previous periods were triggered by physical causes, such as meteorite collision and volcanic eruption, all leading to climate change. The current extinction period is being caused by humans and began approximately 100,000 years ago with the diaspora of humans to different parts the world. By entering new ecosystems which had never before experienced the human presence, humans disrupted the ecological balance by hunting and also possibly bringing disease. From this time up to approximately 10,000 years ago is known as "phase one" of the sixth extinction period.

Conflict exists wherever people and animals live in close proximity and in competition for resources such as water, food or land. It is not a new phenomenon, however it has only recently been examined in any depth.

Partially, this is due to an intensification of the problem as human populations rise and more pressure is placed on natural resources. However, it is also due to a shift in ways of thinking about conservation and the realisation that if biodiversity is to be maintained, the needs of local communities must be taken into account.

This worldwide endangerment of animals and plants is a phenomenon of the 20th century. It is a product of the continuing use of more and more natural resources for a constantly growing human population. Thus, many wildlife species become endangered because there is less wild space for them to inhabit.

Unfortunately, we are witnessing a great wave of extinctions. The current rate may be as high as several species per day. Among the species of most concern are those confined or endemic to a single island or group of islands. These "island" territories can also be cave systems, parks, and reserves that people have created.

When species are isolated, they are vulnerable to environmental changes and natural catastrophes. These are not the only causes of endangerment to species. Hunting and air, water, and land pollution are also responsible for reducing species numbers. So, directly or indirectly, species are becoming threatened because of increasing human population.

Why Species Become Endangered

Species become endangered for a wide variety of reasons. However, when individual cases are grouped and studied, the same broad causes appear again and again:

Rapid habitat destruction is the main reason that species become endangered. Habitat destruction threatens the greatest number of species. Because people need food and shelter, the environments of many species are being eliminated or reduced. In many places, people are turning forests into farmland. Since the early 1990’s, some 12 million hectares of tropical forests have been cleared every year. At this rate within 40 years all remaining tropical forests will disappear. In a worse case scenario, it is estimated that by 2010, the area of tropical forests in Asia, West and East Africa, and Central and South America will be almost depleted.

Natural changes usually occur at a slow rate, so the effects on individual species are usually slight, at least over the short term. When the rate of change is greatly speeded up, there may be no time for individual species to adapt to new conditions. The results can be disastrous. This increase in the rate of habitat destruction is directly linked to the rise in human population. As more people use more space--for homes, farms, shopping centers, and so on--there is less living space for species that cannot adapt to changing conditions. People also affect plant and animal habitats when they take wood, oil, and other products from the land.

Another people-related problem that harms wildlife is the introduction of exotic species - foreign species that are deliberately or accidentally introduced into new habitats by human activities. Sometimes an introduced species causes no obvious harm, but in other cases the introduced species causes serious problems. The worst of these problems is when introduced species begin to prey on native species and cause them harm.

Overexploitation is another reason species become endangered. One example of this is the case of the great whales, many of which were reduced to extremely low population sizes in the mid-20th century because of unrestricted whaling. In 1982 a number of countries agree to put a ban on commercial whaling. As a result, some whale species that used to be endangered have made great comebacks. Many other species, however, are still at risk. Some other animal species experience high rates of exploitation because of the trade in animal parts. Currently, this trade is centered in several parts of Asia where there is a strong market for traditional medicines made from items like tiger bone and rhino horn. Other people-related problems that put plant and animal species at risk include poaching, pollution, and overcollecting.

From the earliest times, hunters have caused the extinction of species. From the Stone Age up to the 18th century, mainly large animals were hunted to extinction. But with the invention of guns, hunters targeted smaller animals and birds. This accelerated the rate of extinction, especially of birds.

Today, in theory, hunting is regulated in most countries, however, it remains a major threat to the survival of many birds and animals. Commercial hunting for ivory, skins, and other products continues to cause the extinction of species. In the 21st century, scientists predict that plant species, such as rare orchids and cacti, will become endangered from hunting and collecting.

Over many years, hundreds of pesticides and other chemicals have run into rivers and accumulated in the soil. This threatens the animal species that feed on plants and other animals. Equally dangerous are the "ghost" nets—discarded or lost fishing nets—that drift in the oceans, trapping and killing fish, seabirds, seals, dolphins, and turtles. Furthermore, industrial gases trapped in the atmosphere pollute the air and cause global warming, changing the environments of species.


Date: 2015-12-17; view: 270


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