One risk of introducing a predator or parasite from a different ecosystem is the non-availability of its controlling agent.
When a new and aggressive species is introduced into an ecosystem, one risk is that it may not have any natural predators or controls in that new ecosystem. So it can breed and spread very quickly and the native organisms may not be able to compete with a species that has no predators.
In conclusion, One risk of introducing a predator or parasite from a different ecosystem is the non-availability of its controlling agent.
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