16 Viewpoint of Modern Ecologij 



munity. It cannot be emphasized too strongly that the community 

 exists because of the suitable reactions of the individuals which make 

 up the community. Therefore, no sharp line exists between the ecol- 

 ogy of the individual and community ecology. All the foregoing 

 concepts will be discussed more fully and illustrated in subsequent 

 chapters. 



The Ecological Complex 



We have traced the development of the concept of the biotic com- 

 munity as the complete assemblage of interdependent plants and ani- 

 mals inhabiting an area. As a further step it came to be realized that 

 the physical conditions of the area must be considered for the com- 

 munity just as for the individual. The organisms interact with each 

 other and also with the physical conditions that are present. Thus 

 organisms and the physical features of the habitat form an ecological 

 complex, or, more briefly, an ecosystem. 



In ecology, as in other subjects, the descriptive view appeared first. 

 Lists of the animals and plants present in characteristic situations 

 were prepared, and values were reported for the physical and chemical 

 conditions of the areas. In time all the important habitats became 

 subjects of special study, including the forests, the grasslands, the 

 deserts, the mountains, and the aquatic regions. Investigations of 

 certain definite habitats gave rise to such sciences as forestry, ocean- 

 ography, and limnology. In other instances studies of special types 

 of environment were not given specific names. 



As various characteristic environments and their biotas were in- 

 vestigated more intensively, the realization developed that the eco- 

 logical complex should not be viewed as a static group of animals and 

 plants with the accompanying climatic conditions. The ecosystem is 

 not a museum group remaining immovable and unchanged as genera- 

 tions of observers pass by the plate glass windows. The community 

 cannot continue to exist without exchanges and interdependencies 

 any more than the individual plant or animal can. The community, 

 as well as the individual organism, is "something happening." Thus 

 the functional viewpoint gained momentimi as modern ecology de- 

 veloped. Sears (1939) neatly emphasized this point by stating, 

 "When the ecologist enters a forest or a meadow, he sees not merely 

 what is there, but what is happening there." 



As the action of the environment was studied in further detail it was 

 found convenient to list its influences as ecological factors. The stu- 



