4 o8 INFLUENCES OF CULTIVATION 



also have been induced in part by the increasing competition 

 for nesting sites caused by fresh influxes of rivals or by 

 the inordinate multiplication of the native birds. 



CHANGES IN FOOD HABIT 



In no way has the spread of cultivation and civilization 

 so clearly influenced the habits of animals as in turning 

 their tastes to new sorts of food. Two causes have fostered 

 this tendency. In the first place the cultivation in large 

 quantities of plants of native kinds and the introduction of 

 new plants have placed before the vegetarian animals of the 

 country a choice such as no native of uninhabited Scotland 

 could have had. The result has been the attraction of many 

 creatures to new foods. I n the second place, the overwhelming 

 increase of some species of animals under the conditions of 

 civilization has created a fresh competition for food between 

 races which depend on the same material, the result being 

 that individuals or races are compelled to seek new sources 

 of supply. 



The changes of habit show several degrees of complexity. 

 They may be simple alterations from one species of food plant 

 or animal to another closely related species; or, more com- 

 plex, from one kind of plant or animal to another entirely 

 different kind ; or, most fundamental change, from animal 

 food to vegetarian food or vice versa. Examples of these 

 different degrees of modification of habit will probably occur 

 to most readers, so that only a few typical illustrations need 

 be given. 



Many animals have shared in the most natural change 

 of all the turning to a different variety of the same kind of 

 food. The caterpillar of the Death's Head Hawk Moth feeds 

 naturally upon the Deadly and Woody Nightshades wild 

 members of the Solanum family (though it has been known 

 to occur on a few other plants). But with the introduction 

 to Europe of the Potato a species of Solanum native in 

 America the caterpillar, attracted by its abundance, has 

 turned to this food plant. It is well to remember, however, 

 that suitable food is but one item making for the success of an 

 animal, and that although every year brings to Scotland fresh 

 Death's Head immigrants from the Continent, so that they 



