All over the world, local natural ecosystems are vulnerable to invasion by plants, animals or microbes that originated somewhere else, having evolved in a different ecosystem, with checks and balances imposed there by the other components of that system.
It is difficult to predict which species, having been imported to Norfolk Island on purpose or accidentally by human carriers, are likely to become obnoxious in their new home. Cats run wild have become a serious threat to native fauna, but dogs do not seem to have run wild in the same manner, as they have done in Australia.
