294 Nutrients 



Many animals, among which birds are prominent, show a predilection 

 for the seeds or fruits of plants, whereas other types eat the flowers, 

 or more frequently, only certain parts or secretions of the flowers, 

 such as the pollen or the nectar. Hummingbirds, butterflies, and 

 bees are well known in the latter category. Finally, the roots of plants 

 form the chief or the exclusive food of some burrowing animals. As 

 a further development of specialization, certain herbivores are re- 

 stricted to a food from plants belonging to a particular taxonomic 

 group, that is, to one family, one genus, or even one species. An ex- 

 ample of selective feeding is shown in Fig. 6.15. 



Carnivores also may sometimes display an epicurean fastidiousness 

 in their diets, but specialization on single animal foods is not as elab- 

 orately developed as it is among herbivores. Certain species of bats, 

 leeches, insects, mites, and ticks, to be sure, are specifically adapted 

 for bloodsucking, and other instances of preference for certain animal 

 tissues exist. Animals specially adapted for subsisting on dead or- 

 ganic matter include the dung beetles and the carrion feeders such as 

 vultures, flesh flies, and sylphid beetles. Various species of scaveng- 

 ers are restricted to the lipoids, proteins, keratinoids, or tendinous tis- 

 sues of the dead animal. For the most part, however, carnivores eat 

 all parts of their prey and are guided largely by availability in their 

 selection of food species. 



The distribution of free-living animals, parasites, and other hetero- 

 trophic forms is obviously closely related to the occurrence of the or- 

 ganisms upon which they depend for food. The nutrient factor limits 

 geographical range in a general way or in a narrowly specific manner, 

 according to the degree to which each species is omnivorous or re- 

 stricted in its food habits. Grazing animals like the antelope are 

 found in grasslands; browsing animals like the deer live in forested 

 regions. Similar broad control of distribution occurs in the aquatic 

 environment. Off the New England coast cod are caught chiefly 

 on the banks, such as Georges Bank, where mollusks, crabs, and other 

 organisms upon which the cod feeds grow abundantly on the firm 

 bottom. In contrast, the redfish is found chiefly in the deeper water 

 off the banks where the soft muddy bottom supports populations of 

 shrimp which form the principal food of this fish (Fig. 8.4). 



Control of distribution on a smaller scale is seen in those hetero- 

 trophic organisms that are limited to one type of food. Monophagous 

 animals are those that eat only one species of food organism. Para- 

 sites generally attack only a limited group of species— sometimes no 

 more than one species. Saprophytes are often capable of deriving 

 nourishment from only one type of organic material, and, if this "sub- 



