II 



THE BIOLOGICAL CONQUEST OF THE WORLD 



Preview. A comparison of two forests • The why of distribution ; 

 barriers ; successions and their causes ; overpopulation and its results • 

 The shifting world of organisms • Ways of locomotion • Adaptability to 

 new conditions • Human interference • Life zones • Life Realms • Sug- 

 gested readings. 



PREVIEW 



The science of Ecology, or the distribution of animals and plants in 

 a given habitat, was considered in the preceding section. Chorology 

 attempts to determine the laws governing the distribution of animals 

 and plants over the surface of the earth. 



So long as man accepted the naive assum]3tion that the earth was 

 originally populated by means of isolated creative acts, there was 

 no point in attempting to explain the distribution of living things. 

 They had all been put arbitrarily in the places where they occurred, 

 and that was all there was to it. With the rise of the belief which 

 culminated in Darwin's famous theory, that dissimilar species have 

 arisen by modification from other species, and that all organisms are 

 related, more or less distantly, to one another, the interpretation of 

 plant and animal distribution became a very interesting and challeng- 

 ing field for study. 



How about the varied populations of living things in arctic, tem- 

 perate, and torrid climates ; the absence of animals and plants from 

 areas quite suited to their existence? Why is it that tapirs are 

 found only in South America and the East Indies, while certain 

 fishes, such as the pickerel, occur only in North America and north- 

 em Europe ? Equally difficult aspects of distribution cropped out, 

 notably in the Australian fauna and flora, which differ so greatly 

 from that of the rest of the world, while most perplexing of all, 

 probably, the habit of migration that makes certain animals, such 

 as birds, seals, salmon, and eels, change residence regularly from one 

 region to another. A gradual suspici(jn that two environments quite 

 similar in general appearance might nevertheless be populated by 

 species of plants and animals different from each other gave the clue 



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