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Invasive Species: Harmful Or Helpful February 18, 2011

Posted by Metabiological in Ecology, Ethics.
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Its a well worn trope in the environmentalist movement: invasive species are bad for local ecosystems and must be destroyed and removed at all cost.  In many cases this argument holds true but we may be coming to the realization that this is not always the case.

A recent study out of Penn State found that the presence of an invasive species, in this case honeysuckle, actually resulted in a positive benefit to the ecosystem.  Not only was honeysuckle positively correlated with the abundance of fruit eating birds that fed on it but it also had a positive affect on other plant species.  That may seem counter intuitive since the major danger of invasive species is that they will outcompete local ones.  What seems to be happening in this case is that since birds congregated in areas rich in honeysuckle plants that shared the same space such as nightshade saw an increase in herbivory as well, thus increasing their seed dispersal.  Now it should be stated that this is one case and there is still plenty of evidence of invasive species being harmful to local ecosystems but it does represent of what I hope will be a change in the way we handle invasions.

Too often our efforts to eliminate invaders is out of a misguided and somewhat naive desire to return environments to their original, “pristine” condition.  One doesn’t need to be a Vulcan to spot several huge logic flaws in this argument.  First of all is the notion that there ever was an original, pristine environment.  At one point or another every species on earth was an invader going all the way back to the first time life struggled out to the land.  More often than not though people don’t seek to return ecosystems to their mythical original state.  Rather restoration experiments usually seem to attempt to return the sites to their original state when humans arrived.  At times this can be for economic or culture reasons and at other times it can be completely arbitrary but it really doesn’t have much to do with the overall health of the ecosystem.  Please note that my objection is not to the idea that restoration cannot be beneficial, it can and often is, only that it is often driven by motivations other than those usually given.

Expanding on that is the rather obvious fact that if we truly cared about removing invasive species and returning them to there original state than there is one species in particular we should be turning our attention to: ourselves (this was actually the subject of a great paper I read and commented on a few months back.) Its no great secret that we are in the middle of the sixth mass extinction this planet has seen.  The difference is that this time it is being driven largely through the actions of a single species.  If we truly cared about this subject we would be advocating the widespread removal (read: destruction) of the vast majority of the human species.  Thankfully, outside of a few marginalized philosophers (Linkola comes to mind) this is not a very popular position.

Another reason often given is that the success of an invasive species is leading to the extinction of local ones.  This is another well worn trope in environmentalism, extinction is always bad, and is on far shakier ground.  Quite clearly the extinction of a species is not always a negative thing.  The eradication of smallpox and the ongoing genocide against polio have not been accompanied by the shedding of tears but rather shouts of joy.  The reason for this is simple: those organisms kill and maim millions of people all over the world and we are far better of without them.  On a similar and more controversial note some biologists have advocated the eradication of mosquitoes in order to contain the spread of malaria.  Leaving aside the massive practical difficulties and what effect this will have on the environments they inhabit (perhaps for another time) the idea should not be rejected out of hand simply for fear of causing an extinction.  After all, parasites are a serious problem.

Of course none of this means that invasive species are never harmful only that a more nuanced metric is need before deciding whether or not to remove them.  There are a variety of factors that need to be evaluated before such an action is taken; what environmental effects is the species having, is it a threat to local wildlife, will it damage the local economy, is there some cultural reason to have it removed?  From a strictly utilitarian perspective weighing the various costs and benefits is a simple (though by no means easy) task.  Of course that is remembering that it is not only the interests of humans that need to be taken into consideration.

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