It depends on what impact that species might have on our environment and our economy and on society. For hundreds of years there have been invasive species and things that have come into Canada and that haven't caused a problem, that haven't taken over ecosystems, that haven't disrupted the balance. But there are also species that do disrupt that balance, and there can be large consequences.
Maybe Tim would like to speak a little bit about the kinds of consequences that some of these things can have.