29 

 The Distribution of Animals 



Now that we have completed a survey of the different kinds of ani- 

 mals that inhabit the earth we shall turn our attention to some of the 

 problems of distribution. Why do kangaroos live in Australia and not 

 in India ; why are there no elephants in South America ; why do some 

 animals imported into a strange environment die out rather quickly 

 while others multiply and become a part of the fauna of the new region? 

 These are some of the interesting questions which are answered in a 

 study of zoogeography, animal distribution. 



The distribution of animals today is explained partly by their history 

 in the geologic past. We know that individual species of animals are 

 not found in all parts of the earth where they can survive. This is due 

 in part to the fact that they have not had the opportunity to get into 

 other regions of the world. When man, either purposely or accidentally, 

 introduces them into a new, favorable environment, they often reproduce 

 phenomenally. There were no rabbits in Australia before 1788, but at 

 that time a number of rabbits were brought in by some Englishmen who 

 thought they might make nice game for hunting. Since then they have 

 multiplied until they have overrun the country and have become a seri- 

 ous pest. They are rounded up and killed by the thousands in efforts to 

 keep them under control. The European starlings were introduced into 

 New York City in 1890, and they multiplied so rapidly that they have 

 now spread over the entire United States and Southern Canada. They 

 roost in great flocks in our cities and make a general nuisance of them- 

 selves. The mongoose is a native of India where it is highly regarded 

 because it kills many deadly cobras ; but, when it was introduced into the 

 island of Jamaica, it not only killed many snakes, but began destroying 

 many of the other native animals. 



Any species of animal will be found in all habitable portions of the 

 earth if it can get there, if it can survive after it gets there, and if it 

 does not change into a new species after it gets there. In general, the 

 older a species, or a group of related species, is in geologic time, the 

 more widely it will be distributed, because it will have had a longer time 

 to reach the various parts of the earth. There are a number of im- 

 portant exceptions to this, however. There are some animals, for in- 



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