Extinction is a term used to refer to the loss of species which are found on the earth’s surface. When extinction occurs it is normally irrevocable and the particular species disappear for ever meaning that some biological aspect of the Earth is lost. The Earth is the only place where living species are found. Extinction can be caused by a number of factors, for instance it can occur due natural calamities which are not predictable such as floods, or drought or it can occur due to man’s activities.
It can also be caused by increased predation due to competition for food, environmental stress, and disease outbreaks. Of late, the rate of extinction has increased because of human beings who have dominated the earth and are a major cause of environmental stress and degradation; this includes increased rates of population, overexploitation of marine mammals, deforestation, among others.
Biodiversity can be defined as to the numerous number of species found on the planet. These species are found on different ecosystems in which they are adapted to. Scientists have managed to identify a large number of these species but surprisingly enough the number of unknown species is estimated to be higher than the number of known species.
Geologists estimate that there are more than 30 million species living on earth although scientist have been able to identify about 1.4 species. Most of the biological diversity is concentrated near the equator and few are found as one move towards the latitudes. Tropical rain forests are believed to provide a habitat of millions of species. This paper looks at extinction are being the greatest threat to biodiversity, looks at the major causes of extinction and concludes with a controversial issue that have risen concerning the rates of extinction.
Loss of biodiversity and extinction
According to Wilson (1992), the worst thing has happened in the 1900s was not depletion of energy sources, nor was it an increase in nuclear war but loss in the biodiversity. The other catastrophes can be repaired within a very short period but loss in biodiversity would take millions of years to correct.
The biggest threat to biodiversity is extinction; this can either occur due to natural processes or can be influenced by human beings. It is estimated that the number of species that have become extinct is greater than the number of species that are currently found on earth. Over the pat two centuries, the rate of extinction is estimated to be one species in every two per year (Anon. “Biodiversity- Biodiversity and extinctions” 2010).
However, in the recent times, this rate has almost doubled and there have been instances of mass extinction. This has been caused by the increase in human actions. From research, it has been known that, most species appear and disappear over a given period of time.
So it is possible that most of the species and families we find today were not present some 500 hundred years ago. For example many families of invertebrates that flourished during the Cambrian era more than five hundred and seventy million years ago are now extinct. Just like animal species, many divisions of plants have been known to appear and disappear over time, this includes the seed ferns, woody plants, pteridospermales, just to name but a few
Causes of extinction
The highest rate of extinction is caused by natural forces. Many species that were originally found on earth have become extinct not because of human activities but because of natural forces such as climate change, disease outbreak, unpredictable catastrophes, and increased rates of predation.
Geological records show that for the past many years, there has been a uniform rate of extinction with some mass extinctions characterized by catastrophic episodes. The Permian epoch recorded the highest extinction rate. Another similar extinction occurred towards the end of the Cretaceous period many million years ago.
To a greater extent, man can be held responsible for the recent mass extinction that is almost surpassing the ones documented in geological records.
This increased rate of extinction has been as a result of over harvesting, distance of their natural habitat, although some arte just victims of circumstances for instance the Vaquita which are normally trapped in nets used for harvesting fish. The increasing rate of extinction is causing an even greater loss of the Earth’s biodiversity (Anon. “Biodiversity- Biodiversity and extinctions” 2010).
The earth is known to be a home of millions of species making it a biodiversity place, however, with the extinctions that are currently occurring, it is losing its biodiversity. This loss is to a greater extent being caused by man’s interference with the ecosystems whereby most rainforest are converted into agricultural land through deforestation.
These lands are not able to maintain a big number of species and most of them become extinct. Tropical ecosystems for instance, the rain forest are habitats for thousands of species and if they are destroyed, the earth losses its biodiversity. Most of these species that become extinct will never occur again meaning that, a part of the earth’s richness is permanently destroyed (Raup, 1991).
Some of the human influences that are believed to cause mass extinctions are over exploitation, introduction of predators, competitors and disease causing organisms, and disturbance of the natural habitat. Most of the species that have been affected by these influences over the past few centuries are the vertebrates.
For instance, nearly 700 species has gone extinct (over the last 500 years) as a result of human activities. That not outstanding, a bigger number of species is at the blink of extinction because they are endangered; about one thousand bird species are endangered and might become extinct after some time (Quammen, 1997).
Human influences that cause extinction
Increase in population
Over the past few centuries, the human population has been growing at a very high rate thereby increasing the rate at which the ecosystems are converted to agricultural land for sustaining this big population. The increase in human population has led to the destruction of almost half of the rain forests found in the world while others have been degraded. This population use most of the fresh water and harvest almost everything that is found in the ocean.
One of the major causes of extinction is overharvesting. Hundreds of specious have become extinct through overharvesting while others are endangered especially the whales. Most of these species are harvested for food, or for commercial purposes. Commercial harvesting is the principal threat in this case.
This includes harvesting fish, rhinos because of their hones, over fishing leads to depletion of resources, reduced biological growth rates and low biomass levels. Sharks are the common type of fish that are over harvested. Over fishing of sharks results in disturbance of the marine ecosystem
Disturbance of the ecosystem
The ecosystem is interfered with due to various human influences for instance deforestation of the rain forests renders most species homeless because their habitat is found in these forested. As they homes are destroyed, they are exposed to their predators who harvest them for food while others die to the harsh environment they are exposed to.
Increased human activities in the ocean such pollution and thermal stratification interferes with the ocean’s ability to act as a carbon sink. For a long time, oceans have been known to store a lot of carbon dioxide. They act as a carbon sink and can hold back more than 50 times of the carbon dioxide in the atmosphere.
However, thermal stratification of the oceans has resulted in a reduction of the ocean’s ability to hold carbon dioxide. Ocean’s can now hold very little levels of carbon dioxide leaving the rest in the atmosphere which consequently results in global warming. On the other hand, the increase in carbon dioxide in the atmosphere causes oceans to acidify leading to the death of the plants found in the ocean with some becoming extinct.
Natural habitats are also being interfered with by global warming. Global warming is the increase in the temperatures of the earth’s air surface and the subsequent increase in the water levels that is, oceans and sea levels increase. It results from numerous human activities that emit gasses they prevent the radiation of sunlight back to the atmosphere.
Generally when sunlight reaches the earth’s surface, there is an amount of it that is reflected back to the atmosphere at a higher wave length; when this happens, the earth’s temperatures are regulated. In cases where the air is polluted by green house emissions then these green house gasses break the reflected sunlight radiations from reflecting back to the atmosphere, leaving them just at the earth’s surface.
Thing increases the earth’s surface temperature. This is not only harmful to human beings, but to all living organisms including plants and animals. When these harmful rays get to the earth’s surface, they absorb most of the moist that helps in the growth of vegetation.
As the growth of vegetation for instance, forest is interfered with, the water cycle changes resulting into shorter periods of rainfall. Growth of plants and vegetation declines consequently resulting in lack of food for both animals and human beings. This increases the mortality rate and some plant species may even become extinct.
A controversial issue about the rate of extinction
There is a controversial issue that has caused scientists to involve themselves in many augments, many scientist disagree with the fact that, the rate of extinction that is recorded in geological books is too high and does not represent a real life situation.
It is assumed that, in every year, more than seven thousand species become extinct; this is rather too high for many people. On the other hand, other scientist hold that, the rate that is recorded is actually too low keeping in mind the increase in human influences. This increased population has to be fed, sheltered and even clothed. There is no other source of resource to cater for this increased population rather than the ones found on earth.
The biggest number of species lives in the rainforest and these forests are being cleared at a very high rate (Anon.” Estimates of the extinction rates” 2010). This means that, the rate of extinction might be actually higher than what is recorded. Statistics taken in 2008 showed that, many species are endangered by human influences and might soon become extinct. The following table shows the percentage of endangered species to the number of evaluated species.
Scientists who disagree with the alarming figures that have been recorded about species extinction argue that, it is not even possible to stop in every part of the world to carry out a research of the number of species that are becoming extinct. Yet there records that estimate the number of species that go extinct on a daily basis, weekly, monthly or even annually.
It is surprising to note that, the estimated rate of extinction exceeds the number of species that have actually being declared extinct through research (Raup, 1991). The high rate of extinction seems to be exaggerated given that, the number of species that have been identified is less than the number that still remains unknown.
The question is how then can it be possible to estimate the number of species that go extinct every day given that most of them are unknown? The majority species are known to have vanished. Where then did the species we find today come from? It is true that, human influences have led to the accelerating rate of extinction of species but at the same time, many urge saving species for their aesthetic value.
Many people have changed their perspective about the environment and have are now using measures of conserving it. Trees are being planted and the government is constantly issuing bans to prevent the exploitation of marine animals. With all these measures being put in place, we expect the rate of extinction to be declining but it seems to be increasing on a daily basis.
Human beings have become more conscious on the role played by living organisms. For instance forests and vegetations are believed to regulate the amount of carbon dioxide in the atmosphere thereby controlling the rate of global warming. Measures have been put in place to ensure that certain areas are left as reserves and most governments have gone to the extent of planting forests. This has created an increase in the habitat of most species and the rate of extinction is expected to go down.
Research has found that, most of the specious that lived many millions years are now extinct. Others keep on appearing and disappearing over time. According to scientist, the rate of extinction that has been recorded over the past two centuries is higher than that which was recorded about 2000 years ago.
Human influences are assumed to have caused the accelerating rate of extinction although some scientists hold that, this rate does not reflect the rear number of species that go extinct every year. They argue that, the rate is too high given that many species have not yet being recognized and the government has been putting measures to conserve some of the ecosystems.
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Quammen, D. (1997). The Song of the Dodo: Island Biogeography in an Age of Extinctions. New York: Simon & Schuster
Raup, D. M. (1991). Extinction: Bad Genes or Bad Luck? New York: W.W. Norton and Company.
Wilson, E.O. (1992). The Diversity of Life. New York: W.W. Norton & Co.