592 



Islands of coralline limestone may have 

 so little capacity for holding water that 

 even in humid areas a typical rock-desert 

 vegetation may develop, as on the small 

 island outUers of the Greater Antilles (e.g., 

 Mona Island, between Puerto Rico and 

 Hispaniola). 



HIGH PLATEAUS 



Related in essential characteristics to 

 both grassland and desert are the two great 

 high plateaus of the world— the Tibetan and 

 the BoUvian. These seem to require con- 

 sideration as distinct biomes because each 

 has a remarkable and characteristic fauna 

 of large herbivores dependent on the 

 grassy plains produced by melting snow. 

 Tibet, in addition to the yak, has a variety 

 of wild sheep and goat antelopes. BoHvia 

 has the remarkable cameUds, the wild 

 vicuiia, and the related domestic llama and 

 alpaca. The animals of these plateaus, in- 

 cluding man, are physiologically adjusted 

 to oxygen deficiency and are cold-hardy and 

 wind-hardy. Many are essentially inhabi- 

 tants of rock desert bordering the watered 

 areas, notably such rodents as the chin- 

 chilla and mountain vizcacha in Bohvia and 

 Peru. Each of these biomes is associated, of 

 course, with a great mountain chain, but 

 from the evidence of endemism, each has 

 been a center of evolution for much of the 

 Tertiary. 



THE TROPICAL FOREST BIOME-TYPE 



In most respects the richest of the 

 biomes are those composed of tropical for- 

 est. These occur on both sides of the 

 equator in a zone of greatly varying width 

 in three major areas, the central African, 

 mainly in the Belgian Congo and Kamerun; 

 southeastern Asia, from eastern India 

 through the East Indian islands to New 

 Guinea and northern Queensland; and the 

 Amazonian, Orinocan, and Guianan basins 

 east of the Andes, with a large extension 

 into Central America. 



The tropical forests are ahke in being 

 of great height, and in having a complex 

 stratification and relatively continuous 

 canopies (p. 482), with a striking develop- 

 ment of associated, often purely arboreal, 

 animals, some with extreme morphological 

 adjustments to their environment such as 

 prehensile tails (mammals, lizards, and 

 snakes). The extremely rich and varied 



THE COMMUNITY 



vegetation is evergreen as a whole, but 

 with some briefly deciduous trees. The 

 forest is characterized by a drapery of 

 Uanas that is unmatched even by the wild 

 grape "jungle" of the southeastern United 

 States. 



The African rain forest (Fig. 225) is es- 

 sentially a continuous single community 

 from the Gulf of Guinea to the great Afri- 

 can lakes and from the Sudanese grass- 

 lands to those of Angola. It has an essen- 

 tially identical outfier in the forest strip 

 along the coast west of the lower Niger, 

 and equally closely related small forest 

 islands extending to the forest strip along 

 the Indian Ocean to the east. A relatively 

 small area of rain forest is found in eastern 

 Madagascar, so distinct in its animal types 

 as to be only remotely related to the Afri- 

 can tropical forest. 



The American rain forest is scarcely less 

 homogeneous than is the African, but dif- 

 fers sharply from the African in its con- 

 tact with the high and continuous range of 

 the Andes and the escarpment of the BoUv- 

 ian plateau. It thus has a subtropical 

 zone of great Unear and areal extent, in 

 contrast with the isolated subtropical for- 

 ests of the widely separate African moun- 

 tains. 



The Oriental tropical forest biome is 

 fragmented in the East Indies, heteroge- 

 neous in that the faunal differences from is- 

 land to island and from archipelago to 

 archipelago are much greater than are the 

 floral, with a major historic faunal break 

 between Celebes and New Guinea. Exten- 

 sive subtropical forests are developed on 

 the slopes of the eastern Himalaya, in the 

 south Chinese mountains, and in New 

 Guinea. 



Details of the vertical stratification of 

 animal fife in tropical forests are beginning 

 to be known with the focus of attention on 

 jungle yellow fever and on the vertical 

 cyclic movements of malarial mosquitoes- 

 Early studies of the forest canopy by Allee 

 (p. 231) have been extended by the Ox- 

 ford University Expedition to British 

 Guiana (Kingston, 1932) and by the Rock- 

 efeller Field Laboratory at Villavicencio 

 (Bates, 1946). 



BIOTIC ZONATION IN MOUNTAINS 



All the major biotic formations exhibit 

 striking relations to the climatic zonation 



