GRAZING AND BROWSING 119 



ceeds to determine the items selected from the available food and the 

 quantity in which each is taken. The work of Petersen, Blegvad, 

 and others at the Danish Biological Station is the most thorough of 

 this type, and is discussed in connection with coactions in the sea. 

 Baker (1916) did some similar work in fresh water, but wuth refer- 

 ence to Mollusca. Bird (1930) made community observations rela- 

 tive to the food of a few birds, but the terrestrial studies in general, 

 even some of the more recent ones, lack the full force of the bio- 

 ecological viewpoint. For example, proportions of the different types 

 of plant or animal food may be given, but the relative amounts of 

 each on the range are not indicated. 



The presentation of coactions from the viewpoint of taxonomic 

 groups, illuminating as it may be to the general biologist trained in 

 this manner, also fails to stress the bio-ecological viewpoint. In addi- 

 tion, it may fail to take account of variations in habits among related 

 species. The American bison {Bison bison L.) is a grassland animal 

 grazing by preference; the closely related European species {Bos 

 bonasus) is a forest dweller, living by browsing. Again, some Carni- 

 vora, for example, the small meerkats in South Africa, have the food 

 habits of prairie dogs, and the small tree hyraces (ungulates) those of 

 raccoons, (cf. Lydekker; he calls the American Bison Bos americanus). 



GRAZING AND BROWSING 



As previously suggested, there is no definite line between the graz- 

 ing and browsing habits. Not only do nearly all grazing animals 

 browse in varying degrees, but there is also no clear-cut distinction 

 either in the original meaning or the current usage of the two words. 

 Moreover, forest undershrubs may be grazed practically like grasses 

 and forbs, while tall herbs are often browsed as though they w^re 

 shrubs. Even more significant is the fact that some ungulates may 

 graze in the summer and browse in the winter, that they may change 

 their food plants as a range becomes overgrazed, or their food habits 

 as they pass from one serai stage into another. In spite of all this, 

 however, nearly all ungulates manifest a distinct preference for one 

 type of behavior or the other (cf. Farrow, 1925). 



Grazing Life Habit 



Grazing animals fall into three classes, arranged in the order of 

 their importance: (a) large cursorial grazers; (6) small grazers resi- 

 dent underground; and (c) small grazers resident among the grasses. 



Large Tramping Grazers. The most representative grazing animals 



