VII. 2 



THE INCREASE OF ANIMAL LIFE 



IN spite of the fact that cultivation has destroyed the 

 breeding-places of many native animals, and has otherwise 

 restricted their range and numbers, it cannot be denied that 

 on the whole it has caused a marked increase of animal life. 

 The effect is clearly seen in the Yellowstone Park in the 

 Western United States, where birds with other animals are 

 preserved, but where, nevertheless, they are not so abundant 

 as in the neighbouring cultivated areas of the States. The 

 same contrast holds good between the cultivated and wild 

 districts of Scotland. The increase of certain species under 

 the influence of cultivation is due mainly to the development 

 of food supplies, and in a few cases to the increase of 

 breeding-sites. In the present section, an endeavour will 

 be made to trace in greater detail the causes to which the 

 increase of animal life may be attributed. 



INCREASE OF VEGETABLE FOOD 



It is a truism that cultivation multiplies the plant-yield 

 of a country, and that the more intense the 

 cultivation the greater is the yield. It is 

 equally evident that herein lies a vastly in- 

 creased food-supply for vegetarian feeders. 

 The result has been undoubtedly to in- 

 crease their numbers, often to such an 

 extent as to make them pests of agri- 

 culture; indeed, through cultivation, man 

 may even be said to create the pests he 

 denounces. Take for example the excep- 

 tionally clear case of the Colorado Beetle 

 in America. When this Beetle, Doryphora 

 (Leptinotarsa] decem-lineata (Fig. 66), was 

 discovered amongst the Rocky Mountains 

 in the region of the Upper Missouri in Fig. 66. Colorado Potato 

 1824, it was restricted in numbers and 

 harmless, for it fed upon the Sand Bur of 

 the wastes (Solanum rostratum\ a wild species of the potato 



Beetles. Slightly larger 

 than nat. size. 



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