Amazon basin
The Amazon drainage basin covers an area of about 7,000,000 km2 (2,700,000 sq mi),[1] or about 35.5 percent of the South American continent.
It is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, and Venezuela, as well as the territory of French Guiana.
[6] Politically the basin is divided into Peruvian Amazonia, Amazônia Legal of Brazil, the Amazon natural region of Colombia, Amazonas (Venezuelan state), and parts of Bolivia and Ecuador.
In the western Amazon hundreds of macaws and other parrots descend to exposed river banks to consume clay on an almost daily basis,[12] the exception being rainy days.
[15] In addition to major differences in behavior and ecology, Amazonian fish vary extensively in form and size.
[21][22] The bull shark and common sawfish, which have been recorded far up the Amazon, may reach even greater sizes, but they are euryhaline and often seen in marine waters.
[25] The Amazon supports very large fisheries, including well-known species of large catfish (such as Brachyplatystoma, which perform long breeding migrations up the Amazon), arapaima and tambaqui, and is also home to many species that are important in the aquarium trade, such as the oscar, discus, angelfish, Corydoras catfish and neon tetra.
[15] Although the true danger they represent often is greatly exaggerated, the Amazon basin is home to several feared fish species such as piranhas (including the famous red-bellied), electric eel, river stingrays and candiru.
[26] Several cavefish species in the genus Phreatobius are found in the Amazon, as is the cave-dwelling Astroblepus pholeter in the far western part of the basin (Andean region).
[27] The deeper part of the major Amazonian rivers are always dark and a few species have adaptions similar to cavefish (reduced pigment and eyes).
The splash tetra is famous for laying its eggs on plants above water, keeping them moist by continuously splashing on them,[32] the South American lungfish can survive underground in a mucous cocoon during the dry season,[33] some small rivulid killifish can jump over land between water sources (sometimes moving relatively long distances, even uphill) and may deliberately jump onto land to escape aquatic predators,[34][35] and an undescribed species of worm-like Phreatobius catfish lives in waterlogged leaf litter near (not in) streams.
In some areas, however, the summer months (June–September) can bring cold snaps, fueled by Antarctic winds traveling along the adjacent mountain range.
There are scattered settlements inland, but most of the population lives in a few larger cities on the banks of the Amazon and other major rivers, such as in Iquitos – Loreto in Peru, Manaus-Amazonas State, and Belém, Pará.
In many regions, the forest has been cleared for soya bean plantations and ranching (the most extensive non-forest use of the land); some of the inhabitants harvest wild rubber latex, and Brazilian nuts.
It is estimated 400 or more tribal groups have lived in the Amazon Basin for hundreds of years with their own culture, language, and lifestyle.
Seasonal floods excavate and redistribute nutrient-rich silt onto beaches and islands, enabling dry-season riverside agriculture of rice, beans, and corn on the river's shoreline without the addition of fertilizer, with additional slash and burn agriculture on higher floodplains.
Extensive deforestation, particularly in Brazil, is leading to the extinction of known and unknown species, reducing biological diversity and adversely impacting soil, water, and air quality.
