Species extinction and Processes responsible for species extinction

Species extinction and Processes responsible for species extinction

Extinction is irreversible natural process and about 99.9% of the species that ever lived on Earth are now extinct. Extinctions are caused by long- term alterations of the environment, such as climate change, or by catastrophic events, such as asteroid impacts or by human activity such as overhunting, habitat destruction, introduction of invasive species, etc.

Like the evolution of new species, extinction is also important in the history of life.  Typically, a species becomes extinct about 10 million years after it evolves and some well adapted species such as sharks and cockroaches remain unchanged for hundreds of millions of years.

Species become extinct for two reasons. Some species die off when their numbers reduce so that they become unable to maintain a successful breeding population. Some species become extinct when they successfully evolve into new species.

Many extinctions in Earth have occurred as mass extinctions, during which 25% or more of all species are wiped out and there have been at least five major mass extinction events in earth’s history. The sixth extinction is currently under way.

Some natural causes of mass extinctions are

Plate tectonics: Continents join together and break apart and land masses also drift which affect environmental conditions including climate, the availability of coastal habitat, and the circulation of ocean currents, etc.

Climate change: Due to sudden climate changes organisms that are adapted to one climate may not be able to evolve fast enough to adapt to the new conditions and may be driven to extinction.

Volcanic eruptions: Volcanic eruptions blow ash, gases and particles into the atmosphere that cause global warming (CO2 and sulfur dioxide), global cooling (sulfuric acid aerosols and dust particles), and acid rain (sulfur and nitrogen oxides) which could bring about extinctions.  Flood basalts, voluminous eruptions of fluid lava cover thousands of square miles. The eruptions also result in changes in ocean chemistry and ocean circulation.

Asteroid impact: An asteroid is supposed to be the reason for the extinctions of the dinosaurs and

many other species on land and in the oceans 65 million years ago.

Humans and Extinction: Now Earth is entering into the sixth mass extinction event and this is due to the destructive effects of one single species, humans.

During the Pleistocene period, wooly mammoths and saber toothed cats were among the large mammals that dominated terrestrial ecosystems. The rising temperatures after the Pleistocene period resulted in the decline of these populations and many went extinct. Humans are at least partially responsible for these and other relatively recently extinctions and this hypothesis is known as human overkill hypothesis. The extinctions were caused because of over hunting, animal habitat destroyed, and alien species and disease introduction. There is a great deal of evidence for the human overkill hypothesis:

·         The post-Pleistocene extinctions did not occur simultaneously around the world. The extinctions closely follow the first appearance of humans on a continent or island.

·         Only large mammals, which are easily hunted, became extinct.

·         Climate change is another factor.

An example of human overkill. Before the arrival of the paleo-Indians, the prairies east of the Rocky Mountains were home to the greatest diversity of large mammals such as mammoths, mastodons, giant ground sloths, buffalo, lions, tigers, and enormous birds of prey. Around 13,400 years ago with the arrival of humans in North America, all of these grand creatures were extinct within 1,000 years.  In Europe and Asia, half the species of large animals, wooly mammoths, elephants, rhinos, giant deer, hyenas, lions, panthers, bison, hippos, and bears were eliminated between 30,000 and 15,000 years ago.

Human caused large numbers of extinctions on oceanic islands where due to the lack of predators, many bird species evolved to be flightless and naive. When humans arrived there the birds became easy prey for people and their cats and rats. Within 500 years of the arrival of the Maori people in New Zealand during AD 1000, the island’s 12 species of giant flightless birds called moas and many species of frogs, lizards, and other birds disappeared. Hawaii lost more than 50 species of birds after the arrival of the Polynesians.

In Africa large animals and flightless birds did not die out in a rapid rate and this is assumed to be due to the fact that, humans did not invade Africa but evolved there.  Because they evolved with humans, the animals are favored by natural selection and many were supremely adapted to running.

The millennium ecosystem assessment by the United Nations Environment Programme (UNEP) found that the current global extinction rate is between 100 and 1,000 times higher than the average over geologic time. Entire ecosystems are being lost or altered beyond recognition. Worldwide, 30,000 species are lost per year, or about 3 per hour.

An endangered species is any plant or animal species whose ability to survive and reproduce has been jeopardized by human activities.

A threatened species is one that is likely to become endangered.

The root of the problem is human population growth, which increased from 6 million when agriculture began 10,000 years ago, to around 900 million at the beginning of the nineteenth century and by the end of the twentieth century the population increased to around 6 billion. All of these people need food, access to clean water and secure shelter and a place for their wastes.

The World Conservation Union (ICUN) projected in 2004 that about 1 million land organisms will disappear in half a century. Harvard University biologist E.O. Wilson predict that one-half of all species on Earth will be extinct by 2100.

 

 

References

 

Emerging Consequences of Biotechnology - Biodiversity Loss and IPR Issues, Krishna Dronamraju, World Scientific Publishing Co. Pte. Ltd.

Biosphere - Ecosystems and Biodiversity Loss, Dana Desonie, Chelsea House