The plateaus and valleys of Bolivia, Peru, Ecuador, and Colombia have been peopled since remote times and saw the rise of not only the Inca and the Chibcha but some of the earliest native civilizations in the Western Hemisphere. Today the Quechua and Aymara tribes are the main indigenous inhabitants of the Andes. Agriculture was the basis of these cultures (the native llama and alpaca were domesticated later), and the lands there are still tilled mainly for subsistence crops. Because of a scarcity of water, however, agriculture is difficult. Tobacco, cotton, and coffee are grown and exported. Copper, silver, tin, iron, and gold are mined, and petroleum has been found. Pack trails are the most efficient means of communication in the Andes. Although there is some rail passage through the mountains, the inhabitants of the Andes do not depend on trains for the maintenance of their economy. Certain Andean areas have developed a tourist trade.