There are many more stories of invasive mammals to tell, and more details untold about feral pigs, foxes, rabbits, cats, squirrels, rats, mice, horses, burros, and other invasive mammals than can easily fit on the printed page. But this overview of mammalian invasions contains many of the basic principles needed to better comprehend the plethora of media stories on invasive mammals.
Many of the invasive mammal examples have been from islands, as scientists prefer to study the simplest possible finite systems before venturing forth to tackle larger continental problems. In other words, the island serves as a laboratory for studying invasions at their simplest. Even in Australia, many rabbit control solutions were first tested on small islands to perfect them before introducing them to the mainland continent.
The invasive mammal problems in some areas are likely to grow worse before they get better. But knowing that many of these invasive species are so successful in their new homes because they left behind the predators, parasites, diseases, and other natural control factors that kept populations under control in their native lands suggests one avenue of control. Namely searching the native lands of the pestiferous mammals for natural control factors that can be safely introduced elsewhere, like the myxomatosis virus introduced successfully into Australia for rabbit control.
However, if nothing else is learned, it is that great care must be taken so that the cures introduced are not worse than the original invasive mammal problems, as was the case with the introduction of the mongoose for rat control. Since humans created most of the invasive mammal problems, it might be reasonable to expect that humans can collectively atone by researching new solutions that minimize the possibility of ecological harm.
In the future, look for clever ecological manipulations of populations, like on the Channel Islands, as well as more mol-
ecular, biotechnology solutions like immunocontraception for rabbits. But rather than expecting the newest technological solution to be the ultimate answer, remember that organisms can and often do adapt, just as the rabbits in Australia built up immunity to the myxomatosis virus and the virus attenuated over time.
If nothing else, the half century of experience with rabbits in Australia points to the need for a control strategy integrating multiple techniques (like the myxomatosis virus plus ripping rabbit warrens) to achieve the best and longest-lasting results. Hopefully, the magic bullet approach of the pesticide era will be replaced with this more comprehensive integrated pest management approach.
However, the human side of the equation must never be forgotten when dealing with invasive mammals, as many of these animals in other non-pest contexts are highly valued. Hence, pestiferous feral cats, rabbits, wild horses, burros, pigs, and other mammals causing problems cannot be treated as the object of extermination like cockroaches or termites. Every mammal seems to be loved by some group, be it hunters and indigenous people who favor wild pigs or animal rights groups who champion freedom for minks. Right or wrong, good or bad, these varied human sensibilities need to be taken into account in designing any integrated pest management program to control invasive mammals. For example, in the western United States, capturing wild horses and letting people adopt them has replaced the old practice of herding the horses into canyons and shooting them. This type of solution may have more to do with politics or social science and consensus building than with biological or ecological principles, but ignoring the human species behind the invasive mammal problems is to invite failure.
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