622 General and Applied Biology 



ecology of a pool or square foot of soil and the biogeography (geographic 

 distribution) of a continent or a certain country. 



In making an ecologic study of a particular plant or animal (or groups 

 of them), the specific heredity of the organisms involved, as well as all 

 the environmental factors, must be taken into consideration. A brief, 

 rather incomplete outline is given, which might be followed in such a 

 study. When this outline is somewhat elaborated, the general problems 

 of ecology, as well as the interdependence of hereditary and environ- 

 mental factors, can be rather easily observed. 



A. Heredity 



1. The Specific Genes of the Organism Being Studied Ecologically. — 



Since hereditary genes (determiners) in the cells of an animal or plant 

 determine to a great extent what the organism is going to be, its struc- 

 tures, its general abilities, its abilities to use certain foods, and its neces- 

 sity to develop in a certain type of environment, it can be seen why 

 heredity must be included in any study of the ecology of that particular 

 organism. The genes of heredity also determine to a great extent the 

 ability of a particular organism to develop variations by means of which 

 it can attempt to fit into its environment, especially if the environment 

 should vary from time to time. The inheritance of the ability to move 

 around or be stationary also influences the ecology of any organism. 

 These, as well as many other inherited factors, determine to a great 

 extent the limits of distribution of a particular organism and conse- 

 quently its ecologic relationships as well. When environments are 

 changed from their normal, the organism living in them may attempt to 

 vary itself sufficiently to continue living in the changed environment; it 

 may, if possible, move to a more favorable environment, or it may die 

 because it cannot accommodate itself to the changed conditions. Each 

 living organism probably has an optimum environment in which it lives 

 most successfully, although in many instances life can continue in changed 

 environments, provided the changes are not too excessive. Animals and 

 plants which do not possess the inherited abilities to vary sufficiently to 

 meet changed environmental conditions have less opportunity of survival 

 under such conditions. 



Certain organisms, such as the common dandelion, are so constituted 

 as to be able to live in a great variety of environments, in many types of 

 soils, in the lowlands and on high elevations. Cranberry plants grow 

 naturally in acid bogs and will not grow in neutral or alkaline soils. 



