Ecology and Evolution - 587 



Fig. 30-12. Pneumatophores of the bald cypress; adaptations to a swampy 

 habitat (see text). (Photo by C. F. Hottes.) 



ECOLOGICAL SYSTEMS (ECOSYSTEMS) 



The ecosystem concept, so named in 1935 

 by A. G. Tansley, has greatly aided the 

 thinking and researches of modern ecologists. 

 The term designates some particular and 

 characteristic section of the environment that 

 is more or less isolated from other sections; 

 but an ecosystem includes also the sum total 

 of interactions among the species inhabiting 

 the region and all interactions between the 

 species and their abiotic surroundings. A 

 balanced aquarium would be a somewhat 

 artificial and exceedingly miniature exam- 

 ple of an ecosystem. Aside from the fact that 

 the aquarium receives light from the outside 

 world, it is virtually a self-sufficient system, 

 which exchanges very little material, either 

 biotic or abiotic, with surrounding environ- 

 mental areas. 



In nature, of course, there are no perfect 

 ecosystems, completely self-sufficient and 

 totally isolated from surrounding systems. 

 However, there are a number of fairly good 

 approximations. Some good examples are to 



be found in ponds or lakes, and in the cen- 

 tral parts of forests, grasslands, salt marshes, 

 and deserts. On the fringes of any such area 

 there are transitional zones, where the par- 

 ticular ecosystem is overlapped by one or 

 more surrounding systems. But disregarding 

 the fringe areas, the ecologist can analyze 

 the main features of the economy of the sys- 

 tem and can reach an understanding of how 

 the plant and animal species of the commu- 

 nity are sustained. 



Analysis of any ecosystem reveals that there 

 is a rough sort of balance in the economy of 

 the community. This balance results from 

 interactions among four principal compo- 

 nents: (1) an abiotic base, which represents 

 the total fund of light and of nutritive sub- 

 stances, provides for the growth of the green 

 plants and other autotrophic organisms; (2) 

 a community of producers, mainly green 

 plants, provides for the primary synthesis of 

 organic foods; (3) a community of consumers, 

 mainly animals, lives upon the available fund 

 of organic food; (4) a community of decom- 

 posers, mainly bacteria and other fungi, de- 



