The Andean region is characterized by a diversity of environmental zones at different altitudes, offering a range of economic opportunities. The region's population has always benefited by exploiting the resources of different zones and by exchange.
The high altitude grasslands supported abundant game and later also herds of domestic camelids (llamas, alpacas and their relatives).
At lower altitudes there are fertile highland plateaux and hillsides, now extensively cultivated using irrigation and terracing. To the east lies the tropical forests of the Amazon basin.
The coast on the west is a desert, fertile only along the numerous river valleys that dissect it and with patches of vegetation on the adjacent foothills.
The coastal waters of Peru are cool, rich in nutrients and low in salt, supporting a diversity of marine life that provides one of the richest fisheries in the world. An annual warm-water current called El NiÒo flows around Christmas-time into the northernmost Peruvian waters; this normally has little impact on coastal resources.
However, occasionally the warm water moves much further south and lasts much longer, with devastating effects. Killing the plankton, the base of the food-chain, a major El NiÒo thus kills or drives away all the other marine life dependent on them.
It can also cause highly destructive torrential rain and consequent flooding in coastal areas. It has been suggested that the sudden collapse of certain coastal cultures, such as that preceding the Chavin, could have been due to a major El NiÒo and its side-effects.
