They change their clime, not their frame of mind, who rush across the sea.
All animals are equal, but some animals are more equal than others.
But the above scenarios of one invader affecting one native, while easier to explain and study, are probably the exception rather than the rule. Invaders seem to beget further invasions, a result of established transportation corridors or pathways, increased vulnerability of recipient site habitats, or a combination of these and other factors. Ultimately, multiple invaders confer negative effects on native systems that are much greater than the sum of the individual exotic species making up the community. Yet, if we wield the sword of extermination as we advance,we have no reason to repine the havoc committed. We learn from history that we do not learn from history.