14 Viewpoint of Modern Ecology 



in general, have been slow to point out that many of the principles of 

 ecology are the same for both plants and animals. 



The modern ecologist strives to understand the fundamental in- 

 fluence of the factors of the environment and to delineate such gen- 

 eral concepts as limiting ai^tion, competition, population growth, and 

 the like. These principles may be applied to the plants or to the 

 animals of the region under investigation, but for many concepts, 

 such as those of the food chain and the dynamics of energy exchange, 

 both the plants and the animals must be considered. The term ecol- 

 ogy thus necessarily includes the interrelations of all kinds of organisms 

 with the environment. 



The Ecology of Habitats and of Individuals 



In the early development of the subject, one group of ecologists 

 concentrated on the relations of the habitat. They strove toward a 

 better description of the habitat and of the influences of the habitat 

 on the plants and animals that lived there. First the physical fea- 

 tures and then the biological influences were investigated. The study 

 of the habitat and its eftects is often spoken of as habitat ecology. 



The work of other early ecologists, instead of beginning with a 

 description of environments, took its departure from an investigation 

 of the individual plant or animal. Attention was focused on the needs 

 and the reactions of the organism and the influence of environmental 

 factors upon it. Thus was developed a study of the ecology of the 

 individual, or to use a specially coined term, autccology. 



The Ecology of Populations and of Communities 



While the habitat ecologists were hard at work, other biologists with 

 ecological leanings were turning their attention to the fact that new 

 interrelations appear when groups arise. No animal or plant lives as 

 a completely isolated individual. When groups of the same species 

 are formed new eftects appear. A simple example will illustrate this 

 point. Suppose that 100 trees are growing as individuals widely 

 spaced in a pasture. The shade from each of these trees will move 

 around during the course of the day so that the ground beneath the 

 trees will receive direct sunlight at least for a time each day. On the 

 other hand, if these same 100 trees were growing close together in a 

 grove, the shadow of one would overlap that of the next, with the 

 result that continuous shade would exist underneath. The effect of 

 the trees in the grove on temperature of the soil, evaporation, and 



