FOREST COMMUNITIES 435 



the different forests of the world have been discussed in the preceding 

 chapter. 



Ground-dwelling jungle mammals exist that are able to climb trees 

 without being predominantly arboreal. Gorillas belong to this type. 

 Their great weight and size limit their climbing. The jaguars, leopards, 

 small cats, scaly anteaters, various rodents, and many insectivores 

 ascend trees on occasion. 



The ground-dwelling mammals tend to be small stealthy forms 

 that wind their way through the forest; such forms include the small- 

 est of all ungulates, the tiny, primitive musk deer (Tragulus) and 

 the forest antelope, Xemorhoedus, of the Malayan region, and 

 Hyaemoschus and the dwarf forest antelope, Cephalolophus, of Africa. 

 In South America these are replaced by the ecologically equivalent 

 agoutis and many other rodents, and by the pig-like peccaries. Certain 

 large African animals such as the okapi, the swamp antelopes, Tragela- 

 phus, and striped antelope Booceros, and the dwarfed hippopotamus, 

 have similar habits. The elephant stands out in contrast as a forest 

 wrecker, moving through the forest by sheer strength. Hippopotami, 

 rhinoceroses, buffaloes, lions, leopards, and even hyenas use the ele- 

 phant-made trails, leaving them yet more passable for other animals. 

 The tapir represents this type of trail-maker in the American jungle. 

 All these animals are active principally at night. 



The tropical rain-forest changes gradually into the gallery forests 

 which are limited to river courses and project far into grassland and 

 steppe regions, producing the savanna type of country. Typical forest 

 forms disappear and are replaced by the teeming life of the forest 

 margins. The tropical forest over-hanging rivers also deviates from 

 type in many particulars, especially in the scarcity of tall forest trees 

 whose giant size cannot be supported in the yielding alluvial soil, and 

 in the increased density of the forest canopy. Unlike the gallery forests 

 such river banks have a decrease in terrestrial and an increase in ar- 

 boreal types, although in tropical America, tapirs and peccaries are 

 characteristic inhabitants. Ground birds are absent, though finches, 

 icterids, and flycatchers, characteristic of the grasslands, invade the 

 river bottoms. Water and shore birds, ibises, kingfishers, herons, and 

 storks enter this habitat via the river highway 48 (see Chap. XXIII). 



The characteristics of the animal population of forest lands arc 

 shown to best advantage in the tropical rain-forest. The further the 

 forest deviates from these conditions — i.e., the less dense the tree 

 trunks, the lighter the forest crown, the more sparing the underbrush, 

 and the richer the growth of grass, the more light penetrating to the 

 ground, the greater the air movement, and the more limited number 



