590 



THE COMMUNITY 



may be designated as the South African, 

 East African, Sudanese, Central Asian, 

 and Mongolian biomes, and in North 

 America as the Great Plains biome (Figs. 

 222, 223). 



The grasslands of South America, the 

 llanos of Venezuela, the campos of Brazil, 

 and the pampas of Argentina and Uruguay, 

 are isolated from those of the Northern 

 Hemisphere. In late Tertiary times, there 

 appears to have been more interchange of 

 animal types than of plants between South 

 and North America. 



In general, the animals of the open lands 

 are by no means incapable of entering and 

 adjusting themselves to forest conditions, 

 e.g., the European forest horse, the Euro- 

 pean bison (wisent), the African forest buf- 

 faloes, and the relatively few, and thereby 

 unduly conspicuous, species of forest ante- 

 lopes. The grassland biome in North 

 America has received such conspicuous 

 attention from Weaver and Clements 

 (1929), Clements and Shelford (1939), 

 and in some scores of papers in EcoloQij, 

 Ecological Monos,raphs, and the Journal of 

 Ecology, that the student is referred to 

 these sources, and to the treatment of the 

 Sirassland communities in the present work 

 for further documentation (p. 466). The 

 grassland border of the Australian desert 

 represents an extremely distinct grassland 

 region, the Australian grassland biome. 



As an example of the historic causes of 

 interdigitation and overlap of grassland and 

 deciduous forest, we may cite the remark- 

 able postglacial phenomena in both Europe 

 and eastern North America of a grassland 

 corridor parallel to the front of the retreat- 

 ing glaciers by means of which various 

 tvpes of plants and animals characteristic of 

 the Central Asiatic and American Great 

 Plains regions were able to spread, respec- 

 tivelv, westward into Europe and east- 

 ward in the United States. (Nehring, 1890; 

 Transeau, 1935; Schmidt 1938; Conant, 

 Thomas, and Rausch, 1945) . The European 

 steppe era is especially well documented 

 by fossils of conspicuous grassland or des- 

 ert types from western Europe (the lion 

 and hyena in Britain, for example) and by 

 living relicts preserved in suitable habitats 

 in the now forested regions. Schmidt has 

 compared the American "Prairie Peninsula" 

 with the European "Steppe Corridor." 



THE DESERT BIOME-TYPE 



Ecologically, the desert communities and 

 their association into biomes are of intense 

 interest for the extremes of adaptation to 

 the desert environment by both plants and 

 animals, and for the conspicuous fact that 

 much of such adjustment is physiological 

 or even behavioral rather than primarily 

 morphological. In their world distribution, 

 deserts range as parallel bordering areas, 

 or as chains of disconnected "islands" or 

 even "continents" of desert alternating with 

 grassland biomes (their area sometimes ex- 

 ceeds that of the associated grasslands). 

 Thus they extend from South Africa to 

 Egypt, from Senegal to the Red Sea, and 

 from Arabia via the Central Asiatic deserts 

 to Mongolia and to India. In South America 

 there is a vast and climatically peculiar cool 

 desert from northern Peru to central Chile 

 west of the Andes, and small and isolated 

 desert areas east of the Andes. In Australia, 

 the center of the continent is occupied by 

 the "Great Australian Desert." 



Desert vegetations are conspicuously 

 composed of thornbushes, perennial suc- 

 culents (especially Cactaceae and Euphor- 

 biaceae), sparse grasses and extremely 

 rapidly growing herbaceous plants (Fig. 

 224). The animal life associated with des- 

 erts is characterized bv fleetness of foot 

 in both mammals and birds; jumping or 

 ricocheting locomotion among mammals: 

 great powers of hearing among mammals; 

 burrowing in all vertebrate types and in 

 many of the deserticolous insects and arach- 

 nids; and extreme physiologic adaptations 

 to food scarcitv and to absence of free 

 water. Animal life in deserts has conse- 

 quently been a favorite source of examples 

 of adaptation. "Desert coloration" is re- 

 markable for the fidelity with which bare 

 soil and bare rock backgrounds are approxi- 

 mated (p. 667), though there are conspic- 

 uously notable exceptions among black 

 animals, some of which may be noc 

 tumal and others associated with black 

 rock (see especially Benson, 1933, for con- 

 cealing coloration in mammals; Parker, 

 1935," Klauber, 1939, Cole, 1943, and 

 Cowles and Bo^ert. 1944, for thermal rela- 

 tions of lizards). Thus lizards, birds, and 

 mammals, among quite tinrelated types, 

 exhibit desert colorations; and fringed toes 

 for traction in loose sand are similarly wide- 



