|i. iitftl (iowiistreain. In l)alaiiCftl cumiiutiiitics, total 

 hioniass of plants must ordinarily be larger than the 

 hioniass of herbivorous animals that feed upon them ; 

 in turn, the biomass of each consumer level must 

 ordinarily be greater than the biomass of the suc- 

 ceeding level that feeds on it. 



Metabolism is even more accurate than biomass, 

 for it represents the rate at which energy is being 

 utilized and work performed. Figure 13-8c evaluates 

 a hypothetical soil population on this basis; we need 

 actual measurements of this factor in every commu- 

 nity. 



Finally, a pyramid may be drawn to show the 

 rate at which new organic matter is produced through 

 reproduction and growth at each trophic level (Fig. 

 13-8d). The basic principle in this pyramid, funda- 

 mental in all types of pyramids, is that the rate of 

 /production cannot he less and will almost certainly 

 be greater than the rate of f^rimary consumption, 

 zvhich in turn cannot he less and zcill almost certainly 

 be greater than the rate of secondary consumption. 

 etc. (Lindeman 1942: p. 408). 



SUMMARY 



In respect to feeding behavior, animals are 

 herbivores, carnivores (predators), omnivores, or 

 saprovores, and have special adaptations for securing 

 particular kinds of food. Various methods have been 

 developed for analyzing the kinds of food that ani- 

 mals consume. Animals discriminate in their choice 



of food depending on its nutritional values, palatahil- 

 ity, size, abundance and availability, and the ])ro- 

 tective devices that the food jMssesses. Relatively few 

 species, however, are restricted to feeding upon a 

 single species of plant or animal prey. 



Concealing coloration is of various types : pro- 

 tective, disruptive, obliterative, and aggressive re- 

 semblance. Bright coloration may be warning of some 

 disagreeable feature that the animal possesses, be 

 mimicry of another species that possesses such fea- 

 tures, or be deflective or directive. 



Food chains commonly contain three to five links : 

 a plant, an herbivore, and one or more carnivores. 

 In eacii community the large number of food chains 

 inter-connect in various ways to form a food web. 

 The relative number of organisms in the different 

 links tends to be constant to give a balance of nature. 



All organisms making up a link in the food web 

 may be considered together as constituting a trophic 

 level, of which there may be five : producer ; and pri- 

 mary, secondary, tertiary, and quaternary consumers. 

 Transformers work over the excreta and dead or- 

 ganisms from all levels. In lower trophic levels, there 

 is generally a greater variety of species, larger num- 

 ber of individuals, higher rates of reproduction, and 

 individual animals are usually but not always smaller 

 in size. A plot of the number of individuals in differ- 

 ent size classes or the number of individuals, biomass, 

 or productivity in different trophic levels takes the 

 form of a pyramid. The relationships shown in these 

 pyramids are fundamental to an understanding of 

 conimunitv structure and dynamics. 



Food and feeding relationships 199 



