If its non-indigenous, then its invasive unless invited. U probably dun agree that humans are invasive as well but u just have to look at what humans did to the oceans.
If you ask me, i'm on the fence on such issues cos on 1 hand, these are invasive species but on the other hand, according to Darwin's theory of evolution, then its fair game, survival of the fittest. If the otters are native to SG, then I'm on the otter's side cos they are rarer and they dun have much land to call home. Dogs on the other hand are domesticated and are known as man's best friend, and so they should be helped and find a proper home for them.
Lets say a common animal like dogs are threatening China's native Panda, what do u think they will do?
Humans as an invasive species are different cos we can out smart most of the large creatures. So humans have to control ourselves, or else, many animals will be wiped out.