The message to policymakers is that you need to monitor more carefully and manage invasions earlier. You should look for exponential growth within a population or the establishment of a second population elsewhere. Rapid deployment of resources is key to the ability to control an invasion. There is a difference between natural and human disturbances, as well as differences in degrees of disturbance. There are also synergisms among different kinds of disturbances that allow invasions to take hold.
Human activities modifying ecosystems cause most of the problems.
There are also public perception problems - if people like a particular plant, they don't want to get rid of it. In order to prioritize limited resources, we can characterize areas as high or low value, and as high or low disturbance, yielding four boxes. Shocking, how easily we have lost a world that seemed so stable and safe. The current emphasis is on control measures implemented once a species has become a major problem. An integrated program of prevention, detection, early control and ecosystem management carried out at all stages of the invasion process is required.