THE ADAPTATION Of ANIMALS TO THE ENVIRONMENT 



793 



10 to 30 inches per year, insufficient to support a forest, yet greater 

 than that ot a true desert. Grasslands are usually found in the interiors 

 of continents— the prairies ot western United States and those of Argen- 

 tina, Australia, southern Russia and Siberia. It appears that early human 

 civilizations developed in this grasslands region, where early man raised 

 grazing animals and cultivated and selected the grasses to produce his 

 prime food plants, the cereals such as wheat and rye. The animals of 

 the grasslands are either grazing or burrowing mammals— bison, ante- 

 lope, zebras, rabbits, ground squirrels, prairie dogs and gophers— and 

 birds such as prairie chickens, meadow larks and rodent hawks. There 

 is a broad band of tropical grassland or savanna in Africa lying be- 

 tween the Sahara desert and the tropical rain forest of the Congo basin. 

 Although the annual rainfall is high, as much as 50 inches, there is a 

 distinct dry season from June to August which prevents the develop- 

 ment of forests. There are great numbers and many different kinds of 

 grazing animals in this region, together with predators such as lions, 

 rhis is the storied "big game country" of Africa. Kangaroos and walla- 

 bies are the grazing animals of the Australian grasslands that are eco- 

 logically comparable to the antelope and zebras of the African savanna. 

 Deserts. In regions with less than 10 inches of rainfall per year 

 vegetation is sparse and consists of greasewood, sagebrush or cactus inter- 

 spersed with sparse grasses (Fig. 38.9). In the brief rainy season the 



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Fiaure 38 10 The rain forest biome: border of a u.auny ... the Ituri Forest of 

 Nala^BelgLn Congo. (Photograph by Herbert Lang; courtesy of The Arr^encan 

 Museum of Natural History.) 



