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In this article we will discuss about the extinction of animals that takes place in a number of ways due to variety of causes.
Speciation (evolution of new species) and species extinction (complete elimination of species) are the natural processes which follow the evolution of animals. It is believed that about 200 species of mammals and birds have become extinct for the last 2000 years. Though there are several natural causes of species extinction but the modern man has accelerated the pace of animal extinction.
The number of a few species of animals has come down to such a small size that if they are not provided immediate protection, they will soon become extinct. For example, the total population of 150 species of birds is believed to be only 2000 at present time, short-tailed albatrosses are only 100 in number and about 100 mammals are facing immediate extinction.
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Extinction of animals may take place in a number of ways due to variety of causes as given below:
(i) It is an established ecological principle that the environmental conditions of any region may change. The change may be gradual and long-term or it may be sudden and short-term. If the environmental conditions of any region change gradually, the animals of that region also try to adjust and adapt to new environmental conditions and sometimes they become successful to survive.
But if the environmental conditions change so rapidly that the animals are unable to adapt to new changed environmental conditions, several species become extinct. In other words, if the rate of environmental change exceeds the rate of adaptation by animals to change environmental conditions, many species become extinct.
The mass extinction of dinosaurs is believed to have been effected because of sudden drop in temperature during the early period of Tertiary Epoch. The dinosaurs having a large body and un-proportionately long tail could not move to other places to escape from the excessive cold and therefore they perished and became extinct.
(ii) The sudden outbreak of disease and pest infections caused by changed environmental conditions of the regions concerned causes species extinctions.
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(iii) Some sudden events like forest fires, volcanic eruption etc. cause species extinction. Violent explosion of Kratatao in 1883 led to mass extinction of species of that island.
(iv) Direct hunting and persecution of species lead to selective mass extinction.
P.S. Martin (1967) has suggested three alternative hypotheses of ‘selective mass extinction’:
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(a) Ecological substitution by other species of large carnivorous animals which compete for the same food resources.
(b) Climatic change accelerates the competition between large mammals for shelter and food.
(c) Over-killing of certain species by man.
(v) Some weaker species become extinct as these perish during the course of competition with most powerful and strongest species.
(vi) Man-induced environmental changes also cause species extinctions. Man changes the environmental conditions both intentionally and unintentionally through a variety of his activities e.g. habitat removal, land use changes, weather modifications, chemical and atomic wars etc. Human activities also alter the equilibrium state of ecosystem which causes extinction of some species at local scale or regional scale.
Man’s continued interference with natural environment at local and regional levels has led to destabilization of environmental and ecological equilibrium and several species of animals are facing threatened extinctions.
According to R. Silverberg (1973) only two kinds of mammals became extinct at world level during 1801-1850; the period 1851-1900 registered upward trend in the species extinction as 31 kinds of mammals became extinct; there were extinctions of 41 kinds of animals in the next period from 1901 to 1944.
It may be pointed out that extinction is an inherent natural ecological process and there is natural balance or dynamic equilibrium between speciation, dispersal and extinction but man-induced extinction may upset this balance which may cause hazardous and disastrous ecological problems to human society.