Amazon biodiversity also plays a critical role as part of global systems, influencing the global carbon cycle and thus climate change, as well as hemispheric hydrological systems, serving as an important anchor for South American climate and rainfall
Piranhas play an important role in their natural environment. As both predators and scavengers, their presence in an ecosystem can affect the distribution of other species of fish.
the biodiversity would be limited and we wouldn't have as many fish types and therefore would limit a lot of the environment. also piranhas bite off broken fins so they help "heal" fish sometimes.