Not long ago, I had the opportunity of attending a University lecture, and the talk was given by one of the top research scientists in invasive species. He noted something that was very interesting; often invasive species might be noticed in an area for quite a while before they became a real problem. That is to say they were in an unfamiliar place, and were growing in numbers, but weren't really hurting anything, or unbalancing the local ecosystem much. They were there, sure, but no real problems at first.
However, much like bacteria colonies operate; once the colony reaches quorum they begin to get quite aggressive - the same occurs with invasive species; pushing out the existing local native species in the ecosystem. Perhaps the biggest question is why? Well, I do have some educated guesses and theories on this I'd like to submit them to you if I might.
It seems when the colonists came to the New World, they were not much problem for the local native Indians except maybe eating the corn seeds to survive that the Indians had saved to plant the next season. Other than that, it turns out both groups became friends, working together, helping one another survive. Perhaps you recall the feasts they had at Plymouth Rock area, later this tradition turned into what we know is Thanksgiving.
However, as the colonists grew in numbers, and more people came over, eventually the new settlers took over. Now then, consider bad bacteria in the body, it often just hangs out, growing its numbers, but not bothering to attack the system, or the good bacteria. However, all of a sudden it seems as if they activate and go after the host. One might ask; why they do this if they are living fairly comfortably inside of that nice new ecosystem?
Now then, also consider Locust, they don't seem to swarm until there are too many of them eating up the vegetation, and then one day they all get really aggressive and go on a rampage. In that case eat up everything in sight, for miles in fact on their journey.
It seems that from small to large, from bacteria to insects to mammals invasive species have similar characteristics when they find themselves in a new domain, new area, or thrust into a new ecosystem. It seems to me that we could study charts and immigration patterns of humans around the planet, or bacteria in the body, and come up with nice mathematical modeling which would help us study the spread of invasive species; for us to get a better understanding. Indeed I hope you will please consider all this and think on it.