Answer:
Due to lack of biological gent.
Step-by-step explanation:
Introducing a new species to a new ecosystem often leads to a disaster because of the absence of bioagent for that species. Bioagent are those organisms which has the ability to control other organisms by feeding on them. A new species does not make problem in its old or original ecosystem due to the presence of controlling agents but in the new ecosystem there is no bioagent that can stop its growth so that's why sometimes the introduction of new species leads to a disaster.