To date, at least 40,000 plant species, 427 mammals (e.g. jaguar, anteater and giant otter), 1,300 birds (e.g. harpy eagle, toucan and hoatzin), 378 reptiles (e.g. boa), more than 400 amphibians (e.g. dart poison frog) and around 3,000 freshwater fishes¹ including the piranha have been found in the Amazon.

These numbers are dwarfed by estimates for the smaller life forms: just in Brazil, between 96,660 and more than 100,000 invertebrate species have been described by scientists.²
 

Why are there so many species?

Well, consider life in the Arctic. You are subject to intense climatic conditions (very cold, often windy), food is scarce, and places to hide from predators are hard to find - clearly not the best environment for wildlife to thrive.

Now contrast that to the tropics, where the climate is warm (but liveable), prey is plentiful and there are many ecosystems where wildlife can live.

Over time, these factors have made it possible for species to adapt to different conditions and develop habitat specializations, resulting in the vast species richness of places such as the Amazon Basin.
 

Amazon wildlife: what happens in the wet season?

For plants and animals, the seasonal rains that cover parts of the Amazon are a catalytic event; some animals switch diets, while others are suddenly on the move. Here, a turtle will leave the main river and seek the refuge of a pool further inland; further, wading birds migrate north to the upper waters of tributaries.

The wet season also affects the timing of animal reproduction. For example, the arthropods, a family of insects, are more abundant at the end of the dry season and the beginning of the rainy season³.
 

…when it gets dry again

With the wet season behind them, Amazon wildlife such as monkeys, cats, iguanas and various lizards abandon deciduous trees (shed their leaves seasonally), which no longer have leaves, and relocate to riverine gallery forests, where there are still leaves⁴.

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¹Da Silva et al. 2005. The Fate of the Amazonian Areas of Endemism. Conservation Biology, 19 (3), 689-694
²Lewinsohn T. M.and Prado P.I. 2005. How Many Species Are There in Brazil? Conservation Biology. 19 (3), 619
³Lieberman and Dock, 1982 in Kricher, 1997
⁴Kricher, 1997