ABSTRACT
The two major watersheds of the South American continent are the Amazon watershed and the La Plata watershed. The Amazon watershed has a large number of tributaries and associated floodplains, wetlands, inundated savannas, and inundated tropical forests. Fisheries production is correlated positively with the inundation pulses and low water levels can produce large fish mortality, especially during the “friagem” period. The water from the inundation pulses accelerates the biogeochemical cycles, which is a fundamental forcing function for the different communities. When the water level decreases, organic detritus, aquatic macrophytes, and plank-tonic organisms are drained to the rivers increasing the concentration of carbon, nitrogen, and phosphorus in the rivers. The inundation periods and the transition regimes of water level disperse organisms and resistant eggs, promoting a large-scale strategic process of survival adaptations for several plants and animals. The studies of the evolution, speciation, and distribution of freshwater fishes were carried out on the Great African lakes and in other aquatic systems.
