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Newler argues that, "animals become extinct when they die and no longer exist; at that death of the only existing members of the species. Extinction simply means to be away forever". The process takes place over a period of time. A species may be regarded to as functionally extinct before it is fully extinct when only a few of them exist. The existing group is for one reason or another unable to reproduce and propagate the species, hence termed as functionally extinct. The process begins from the time when the death rate is higher than the birthrate. The number of animals then slowly decreases to extinction, (Newler, 102).
Newler also adds that in biology extinction is the end of a given species of animals in an ecosystem. Though not documented, scientist believe that 99.9% of the species that have existed before have so far been extinct. A certain species of animals may get extinct because it cannot survive in the changing environmental conditions; allowing only the species that are well adapted to the environment to survive. This shows that there are certain natural factors within the environment that causes extinction, (Newler, 102).
According to Manwel, a number of animals that existed several years ago have since been extinct. These include: "tyrannosaurus Rex (extinct 65 million years ago), Steller's sea cow: the defenseless beast (extinct since 1768), Thylacine: the Tasmanian tiger (extinct sine 1936), Quagga: half Zebra, half Horse (extinct since 1883), Irish Deer: the largest deer that ever lived (extinct about 7,700 years ago), Caspian Tiger: the third largest (extinct since 1970), Aurochs: a very large type of cattle (extinct since 1627), Great Auk: largest of all Auks (extinct since 1844), Cave Lion: one of the largest lions ever (extinct since 2,000 years ago) and Dodo: the archetype of extinct species (extinct since late 17th century)", (Manwel, 75)
Causes of animal extinction
Although some cases of animal extinction is attributed to natural factors within the environment, it is however evident that human activities play a very key role in the process. Scientists have studied the human activities that causes immense environmental changes which makes the environment unfit for the existence of a particular species of animals. Since humans have become the dominant species on earth, increase in human activities leads to exploitation of the resources within the environment and leads to emissions that may cause serious climatic changes which reduce the chances of survival of the animals. Some of the causes of extinction include the following.
According to Manwel, "there is a close association between global warming and extinction of animal species on earth. Scientist argue that 251 million years ago, life on earth nearly came to an end when there was mass extinction that saw the death of over 90% of all species on earth. This was caused by a volcanic eruption that caused an increase in atmospheric temperatures by 6 oC setting off a greenhouse effect that led to the mass extinction. The greenhouse effect was caused by the emission of carbon dioxide from the volcanic eruption". The accumulation of carbon dioxide in the atmosphere creates greenhouse effect, (Manwel, 77).
Ruckler adds that with the increase in human activity and industrial advancements lead to the emission of carbon dioxide in the atmosphere which causes greenhouse effect. As the levels of carbon dioxide increases, the evidence of its effects on the planet becomes more glaring. At present, a number of animal species are at the verge of extinction because of the serious environmental changes cause by global warming. Global warming leads to increase in atmospheric temperatures and reduces the amount of oxygen both in the atmosphere and the water bodies. This greatly affects the existence of animals. For example, when the amount of oxygen dissolved in water is reduced, anaerobic bacteria increases and the number of the other aquatic animals reduces drastically. Global warming also affects migration of animals, hatching of eggs and distribution of animal species in the planet. There is factual evidence that global warming is tied with animal extinction. In Australia for example, White Possum is believed to be extinct as a result of global warming. The animal died because it could not withstand the high temperatures, (Ruclker, 56).
Overhunting and overfishing
According to Raloff, "overhunting refers to the harvesting of wild animals beyond the growth rate of the population; such that the total population of the animals gradually reduces". Both overhunting and overfishing reduces that number of animal species. For example, a number of fish species are facing extinction because of overfishing. Overhunting in the high seas has reduced significantly the population of whales, sea turtles, sea cows and other fish species, (Raloff, 23).
Most humans hunt for wild animals for their hides and meat. Human encroachment into the forest and new habitat has seen the extinction of animal species. In North America, 11,000 years ago, when people first migrated from Serbia to Alaska, it is thought that some species of animals including the mastodon, mammoth and Saber-toothed tiger became extinct within a few centuries because of hunting and resource exploitation.
The effects of global warming are evident from the extinction of a member of the primate group in Ghana and Ivory Coast. The red colobus and the red-checked monkey became extinct from the African forest because overhunting and destruction of its habitat brought about by human inhabitance.
Raloff argues that "in the past, the extinction of animals such as elephant birds and lemurs in Madagascar, kangaroos in Australia, Moas in New Zealand, herbivores in America are overhunting. Hunting poses major threat to animals and has lead to the increase in the number of endangered species". The most endangered groups of animals in the world today are the mammals and birds. For mammals the main disadvantage they have is that they are big (require more food and water) and reproduce at a slower rate hence they can be easily wiped out through overhunting. Birds are susceptible for overhunting because of their conspicuous nature. This makes the two goops the most endangered groups in the modern world, (Raloff, 23).
Manwel and Mwenda pointed out that most animals live well in given set of condition provided in a given habitat. Habitat degradation means that the conditions are altered making it unsuitable for animal inhabitance; which may cause the extinction of a species of animals, which directly depend on the environment for food and shelter. The environment is changing from time to time in a slow pace. Human activities cause rapid changes in the environment to the disadvantage of animals which are slow to adapt to the fast changing environment. Increase in agriculture, mining, logging and fishing are just but a few human activities that expedite the extinction process through environmental degradation, (Mwenza, 96).
Habitat degradation may cause extinction of animal species either directly or indirectly. The industries and farms produce a lot of toxic products. The effects of these products include; reduced reproductive capacity, short life span and reduces that ability of the animals to survive the environmental conditions. The availability of food and shelter from the environment is reduced by habitat destruction.
Manwel and mwenda said that "overpopulation in animals stiffens the competition for food and shelter". When the population of animals is higher than the carrying capacity of a given ecosystem, there will be a shortage of resources which definitely leads to the death of some animals. Overpopulation leads to overexploitation of the existing resources. When there is overpopulation of predators, the population of the prey reduces to and becomes one of the endangered species. If the increasing population of the predators is not controlled, the prey soon becomes extinct, (Manwel and Mwenda, 29).
The number of endangered species in animals increases with time. This means that the total population of animals on earth reduces gradually. A number of animal species are now facing extinction. The main causes of extinction can be either natural causes or human activities that affect those animals directly or indirectly. The causes include: global warming, overhunting and overfishing, overpopulation and habitat degradation. The main effects of these factors is that they endanger some animals species.
Manwel, Paula. and Mwenda, J. Earth's Endangered Creatures. 5th ed. New Jersey: Prentice-Hall, Inc, 1998.
Newler, Martin. Disappearing Species. London: McGraw-Hill publishers, 2000.
Raloff, Geoffrey. Extinction and Environmental Changes. 2nd Ed. Boston: Allyn & Bacon publishers, 2004.
Ruckler, Benjamin. Species Disappearing at an Alarming Rate. (3rd Ed.). New York: John Wiley & Sons, Inc, 2006.