Ecologic Study of Living Organisms 623 



Cacti grow best in arid soils and will not grow in poorly aerated, wet 

 soils. Citrus fruits and palms of the tropics will not grow in habitats 

 with freezing temperatures. Because of the hereditary factors in the 

 grain of corn, a corn plant will be a corn plant, but the specific way in 

 which it develops will be determined by many environmental factors 

 which influence its growth. The common earthworm might be abun- 

 dant in a moist soil well supplied with humus and organic food, while 

 it might be very scarce, or entirely absent in a dry, sandy, abrasive soil 

 with little or no available food. 



2. The Inherited Abilities and Reactions of the Organism Being 

 Studied. — All animals start their life by inheriting certain capacities to 

 develop in a particular way. If the environment is not of the type to 

 permit that development, the animal may move elsewhere, it may at- 

 tempt to alter its environment, it may develop abnormally by remaining 

 in such adverse environment, or it may be killed by such adverse en- 

 vironment. In some animals development must take place in a rather 

 uniform environment in which conditions change very slightly. In other 

 animals development must take place in an environment in which con- 

 ditions are constantly changing in a very definite order. It is easily seen 

 that one type of animal described above cannot well develop in the other 

 environment and vice versa. 



An example of inherited abilities and reactions which have influenced 

 the ecologic relationships and distribution is that of the EngUsh sparrow. 

 If this common bird had not possessed in many successive generations a 

 tendency to be unafraid, its distribution today would be quite different 

 than it is. Because of its inherited lack of timidity, the sparrow has had 

 protection and a generous supply of foods most of the time. In fact, 

 the sparrow has followed man and has taken advantage of all of its 

 opportunities. Not being afraid, the sparrows are said to have entered 

 the empty grain cars in the East and, after the doors of the cars were 

 closed, have rather contentedly "hitch-hiked" their way to the West. 

 Their inherited lack of temerity aided them no doubt in their distribu- 

 tion. Would one have expected such birds as blue jays, with entirely 

 different inherited reactions, to have been transported easily and quickly 

 across the continent? What happened to the West after the rapid in- 

 flux of these birds from an ecologic standpoint? The inherited ability 

 of sparrows to build their nests anywhere and from all kinds of materials 

 also influences their ecology, while other birds require nesting sites and 

 nesting materials of more specific qualities. 



