Invasive species impact ecosystems - a statement that does not lead to great debates, controversies or arguments. The amount or the type of impact on the other hand can raise the dander level and inspire emotional responses. How much impact does one Alaskan pike in a fishing hole near a salmon run have? If one has no impact, how about two? At what point do you think there is a problem? If one is not a problem and a fishing pond, now devoid of any species except for the small pike-fry that can never grow up, is a problem, at which point (number) did the species count move from no problem to a problem? One answer is that one species is too many, and that the best defense is early detection and rapid response (eradication).
Implementing this strategy requires knowledge of native species, and the a priori assumption that exotic alien species are not allowed until otherwise proved or held harmless to the system. What do we do about “novel” ecosystems that are the present result of human disturbance of the environment at a local level? We can try to repopulate the novel system with known natives, but that presents some unintended consequences of its own. For we either bring back the top predators, mountain lions in Washington, DC, for example, along with the beautiful butterflies and song birds or we create our own new partially “native” but non indigenous system, a novelty in and of itself. And to confuse things further, native is defined by coordinates in space and time which assumes a level of carbon dioxide around 280ppm. What exactly is native at 380ppm of CO2 or even higher levels?
Measuring the impact of a non indigenous, non native, exotic, alien species assumes a negative quality or quantity. This assumption is based on human need for simplification and our tendencies to reduce all issues to a black or white, true or false set. A problem can be reduced to either 1 or 0, and invasive species are reduced to bad, negative or 0 in the general framing of invasion biology. Similarly climate change is framed as a negative physical phenomenon. And of course invasive species and climate change interact one with another adding another layer of complexity that our yes or no system tries to reduce.
The desire for simplification of complex non linear problems produces the wicked inconvenience of unexpected consequences and unintended outcomes. A classic case of this type of collision of desires is occurring as saltcedars invade riparian ecosystems of western North America. The enormity of the ecological change quickly lent itself to the all or nothing saltcedars are bad judgment with little or no argument. And yet, one species has found shelter in the saltcedar; under certain conditions, the southwestern subspecies of the willow flycatcher (SWWFC), Empidonax traillii extimus, whose natural range is being altered by changes in climate and by changes in vegetation, selects the invasive species for its nesting. The immediate problem of harm to an endangered species versus the long term harm of the invasive species to the native ecosystem is confused by the improbable use by one species of another. And efforts to control the invasion become entangled with desires to preserve another. The bad saltcedar now has some good within it, even while at the same time it should never have been allowed to establish in the first place. Saltcedars moreover can probably be controlled with the intentional introduction of yet more non native organisms in the form of insect species which will over time reduce the invasive species and allow the restoration of the native vegetation assuming that climate parameters do not change faster than the invasive species can be brought under control. In addition this introduction will create as a by-product more novelty in the natural system that we first set out to protect.
We are in fact gardening on a large scale. We are geo-engineering the landscape and the ecological systems in order to protect, enhance and preserve the resources and services that our native ecosystems even as they change before our eyes and beneath our feet. Each decision is not so much a good or bad choice but rather a combination of how much good and how much bad. We must come to terms with the concept of vagueness in nature, uncertainty in process, and the use of fuzzy logic when we need it to make informed choices.