If the issue is change in natural distribution and the species is expanding its range, say from the United States into Canada, such as we're seeing now, they aren't considered alien. That's a part of the very natural change you alluded to that's happening in ecosystems. That's not to say that some of the species that are expanding their range naturally into Canada because of changing ecosystems aren't going to be harmful. We may still need to deal with those species as a country. Mountain pine beetle is a really good example of that. It's not an alien species to Canada; it was always found in British Columbia.
On October 4th, 2011. See this statement in context.