ECOtOGY 755 



by decomposer organisms, bacteria and fungi, which break down the 

 organic compounds of dead protoplasm from producer and consumer 

 organisms into inorganic substances that can be used as raw materials by 

 green plants. 



No matter how large and complex an ecosystem may be, it can be 

 shown to consist of these same major parts— producer, consumer and 

 decomposer organisms, and nonliving components. 



327. Habitat and Ecologic Niche 



Two important concepts which are basic to the description of the 

 ecologic relations of organisms are the habitat and the ecologic niche. 

 The habitat of an organism is the place where it lives— a physical area, 

 some specific part of the earth's surface, air, soil or water. It may be as 

 large as the ocean or a prairie, or as small as the underside of a rotten 

 log or the intestine of a termite, but it is always a tangible, physically 

 demarcated region. More than one animal or plant may live in a single 

 habitat. 



The ecologic niche is the status of an organism within the com- 

 munity or ecosystem and depends upon the organism's structural adap- 

 tations, physiologic responses and behavior. E. P. Odum has made the 

 analogy that the habitat is an organism's "address" and the ecologic 

 niche is its "profession," biologically speaking. The ecologic niche is an 

 abstraction that includes all the physical, chemical, physiologic and 

 biotic factors that an organism requires to live. To describe an organ- 

 ism's ecologic niche, one must know what it eats, what eats it, its range 

 of movement, and its effects on other organisms and on the nonliving 

 parts of the surroundings. 



The difference between these two concepts may be made clearer by 

 an example. In the shallow waters at the edge of a lake one could find 

 many different kinds of water bugs, all of which have the same habitat. 

 Some of these, such as the backswimmer, Notonecta, are predators, catch- 

 ing and eating other animals of about its size, while others, such as 

 Corixa, feed on dead and decaying organisms. Each has quite a different 

 role in the biologic economy of the lake and thus each occupies an en- 

 tirely different ecologic niche. 



328. The Cyclic Use of Matter 



The total mass of the organisms that have lived in the past billion 

 or so years is much greater than the mass of the entire planet. The Law 

 of the Conservation of Matter, which is firmly established, assures us 

 that matter is neither created nor destroyed; obviously, then, matter 

 must have been used over and over again in the formation of new gen- 

 erations of animals and plants. The earth neither receives any great 

 amount of matter from other parts of the universe nor does it lose 

 significant amounts of matter to outer space. Each element-carbon, 

 hydrogen, oxygen, nitrogen, phosphorus, sulfur, and the rest-is taken 

 from the environment, made a part of living material and finally, per- 

 haps by a quite circuitous route involving a number of other organisms, 

 is returned to the environment to be used again. An appreciation of the 



