Ecologic Study of Living Organisms 633 



(d) Quantity and Quality of Usable Foods: All animals require 

 foods of animal or plant origin. Some types require specific foods of 

 definite qualities. If such foods are lacking, the animal may die, or the 

 lack may cause it to move, if possible, to a locality in which desirable 

 foods are present. Other types of animals are not so specific in their 

 food requirements and can exist on a great variety. The latter types 

 of organisms are not so easily affected by the scarcity of any particular 

 kind of food. Animals may be classified according to the types of foods 

 utilized. Organisms depending upon animals for food are known as 

 carnivorous (flesh-eating) ; those depending upon plants, as herbivorous 

 (plant-eating) ; those which utilize both animal and plant foods, as 

 omnivorous (all-eating). Animals of one of the above types may be 

 compelled to change their habitat because of the quality and quantity 

 of the particular foods they require in that community. 



All living plants require foods of one type or another. In some in- 

 stances their requirements are very specific and in others they are more 

 general. If an area has a limited amount of food of a specific quality 

 and plants require this kind of food in large quantities, it is quite evi- 

 dent that plant distribution will be affected accordingly. In some 

 instances the foods present are in a form which is not usable. This fact 

 also will be of importance in the determination of dispersal of plants. 



(e) Ease and Efficiency of Waste Elimination: The ease with which 

 detrimental wastes can be successfully removed from the environment 

 of an animal no doubt affects its ecology. Since wastes, if allowed to 

 accumulate, are detrimental to living protoplasm, it is necessary that 

 the animal live in a habitat in which they can be quickly removed as 

 they are formed. If a certain environment cannot accomplish this suc- 

 cessfully for an animal, the animal will attempt to find a more favor- 

 able habitat. Thus, wastes may be a factor in animal ecology. The 

 removal of wastes from a plant may be a minor factor in its ecology, 

 but together with other minor factors may be quite influential. Under 

 normal conditions, wastes are rather effectively removed from plants, 

 but in case they are not they could be partially responsible for some of 

 their peculiar behaviors. 



3. Biologic Factors. — 



(a) Competition for Food, Light, Moisture, Space: If too many ani- 

 mals with the same food requirements are present in an area with 

 limited quantities of usable foods, there will be a stiiiggle between them 



