new species that are introduced into an ecosystem can upset the balance of the ecosystem; for example, the invasive species can prey on many populations without its population being regulated by any natural predators.
Invasive species in the Amazon Rainforest
The wild boar, which is native to Europe and Asia, was introduced into the Amazon rainforest; it has greatly increased in population due to its small number of natural predators; it has also brought diseases from Europe that harm Amazonian species; finally, it consumes large amounts of flora and fauna and destroys crops (Biodiversity)