BIOGEOGRAPHY 



atic enquiry, I happened to read for amusement 'Malthus on Population,' 

 and being well prepared to appreciate the struggle for existence which 

 everywhere goes on from long-continued observation of the habits of ani- 

 mals and plants, it at once struck me that under these circumstances 

 favourable variations would tend to be preserved, and unfavourable ones 

 to be destroyed. The result of this would be the formation of new species. 

 Here then I at last got a theory by which to work; but I was so anxious 

 to avoid prejudice, that I determined not for some time to write even the 

 briefest sketch of it." 



DISCONTINUOUS DISTRIBUTION 



The actual distribution of many organisms presents problems which are 

 very difficult to understand if it be assumed that, in the words of Linnaeus, 

 "There are just so many species as in the beginning the Infinite Being 

 created," and if their present distributions correspond to their places of 

 origin. Thus, the same or closely similar species sometimes exist in widely 

 separated places, with no representatives in the intermediate territory. 

 Alpine species are frequently identical with, or closely similar to, species 

 much farther north. Organisms separated by great physical barriers are 

 usually quite different, even though their physical surroundings may be 

 much the same. Yet the fossil organisms of a particular area are usually 

 similar to those now living in the same area. Finally, the inhabitants of 



SNOW I rcc 



. SNOW LINE 



MOSSES & LICHENS 



LOW HERBACEOUS VECETATIOM 

 -TREE LINE 



Ty^ 



Figure 2. Comparison of Latitudinal and Altitudinal Life Zones in North 

 America. (After Wolcott, from Allee, et al, "Principles of Animal Ecology," W. B. 

 Saunders Co., Philadelphia, Pa., 1949.) 



15 



