20 Viewpoint of Modern Eeologij 



own species. At the moment man is suffering from lack of these 

 adjustments. 



APPROACH TO THE STUDY OF ECOLOGY 



The study of ecology is best begun through the analytical approach. 

 This involves the delineation of the individual influences of the en- 

 vironment and the recognition separately of the various activities of 

 the organisms present as steps toward building an understanding of 

 the entire dynamic interaction between the complete environment 

 and its inhabitants. 



The fundamental relationships are most readily grasped by analyz- 

 ing the simplest situations first. Contrast, if you will, the ecological 

 dependencies of an alga living near the surface in the open ocean 

 with those of a tree growing on land. The tissues of the alga receive 

 their energy supply directly from the sun and they carry on their inter- 

 change of materials directly with the surrounding water, which is 

 uniform and extremely constant in respect to the ecological factors 

 concerned. The tree, on the other hand, is partly in the light and 

 partly in the dark. Part of the tree is surrounded by the atmosphere 

 with its widely fluctuating temperature and humidity; part is in the 

 soil, where it is subject to a very difterent temperature and is alter- 

 nately flooded with air and with water. The part of the tree that is 

 above ground must deal with one set of organisms, and the part of the 

 tree below ground is concerned with an almost entirely different set. 



Another reason for adopting the analytical approach is that this 

 procedure is more likely to reveal limiting factors. All animals and 

 plants tend to grow, to reproduce, and to disperse until checked by 

 some influence of the environment. The factor that first stops the 

 growth or spread of the organism is called the limiting factor. It is 

 not always easy to single out the limiting factor, and sometimes two 

 or more factors combine to provide the limiting influence. Never- 

 theless, it is extremely desirable whenever possible to determine what 

 agent or agents control the natural tendency of the plants and animals 

 present to increase in size, numbers, and range. In the investigation 

 of any natural area correlations will be found between features of 

 the environment and the activities of organisms present. Analysis of 

 the action of individual influences at work in the habitat is necessary 

 in determining which of the correlated factors are actually causal 

 factors. Suppose, for example, that we discovered a correlation be- 

 tween the occurrence of the factor A and organism B. Should we 

 conclude that A causes B? 



