776 ANIMALS AND THEIR ENVIRONMENT 



been found more effective to modify the community than to attempt 

 direct control of the species itself. For example, the most effective way 

 to increase the quail population is not to raise and release birds (arti- 

 ficially "stocking" the area) or to kill off predators, but to develop and 

 maintain the particular biotic community in which quail are most suc- 

 cessful. 



Although each community may contain hundreds or thousands of 

 species of plants and animals, most of these are relatively unimportant 

 and only a few, by their size, numbers or activities, exert a major control 

 of the community. In land communities these major species are usually 

 plants, for they both produce food and provide shelter for many other 

 species, and many land communities are named for their dominant 

 plants— sagebrush, oak-hickory, pine, and so on. Aquatic communities, 

 with no conspicuous large plants, are usually named for some physical 

 characteristic— stream rapids community, mud flat community and sandy 

 beach community. 



In ecologic investigations it is unnecessary (in fact it is usually im- 

 possible) to consider all of the species present in a commvmity. Usually 

 a study of the major plants which control the community, the larger 

 populations of animals, and the fundamental energy relations— food 

 chains— of the ecosystem will define the ecologic relations within the 

 commimity. For example, in studying a lake one would first investigate 

 the kinds, distribution and abundance of the important producer 

 plants, and the physical and chemical factors which might be limiting. 

 Then the reproductive rate, mortality rate, age distribution and other 

 important population characteristics of the important game fish would 

 be determined. A study of the kinds, distribution and abundance of the 

 primary and perhaps secondary consumers of the lake which constitute 

 the food of the game fish, and the nature of other organisms which 

 compete for food with these fish, would elucidate the basic food chains 

 in the lake. Quantitative studies of these would reveal the basic energy 

 relationships of the whole ecosystem and show how efficiently the inci- 

 dent energy is being converted into the desired end product, the flesh 

 of game fish. On the basis of this knowledge, the lake could intelligently 

 be managed to increase the production of game fish. 



Most of the studies of biotic communities made to date have been 

 of regions in the arctic or desert, where there are fewer organisms, and 

 their relatively simpler interrelations are more easily analyzed and 

 understood. A thorough ecologic investigation of a particular region 

 requires that it be studied throughout the year for a period of several 

 years. The physical, chemical, climatic and other factors of the region 

 are carefully evaluated and an intensive study is made of a number of 

 carefully delimited areas which are large enough to be representative 

 of the region but small enough to be studied quantitatively. The num- 

 ber and kinds of plants and animals in these "study areas" are estimated 

 by suitable sampling techniques. Estimates are made periodically 

 throughout the year to learn not only the components of the com- 

 munity at any one time but also their seasonal and annual variations. 



