“Bringing an invasive species and introducing it into a new foreign range is one of the worst things that can happen to an ecosystem and its biodiversity”. I’m sure you’ve heard some sort of variation of this statement before, especially if you live in Florida, Australia or some other Invasive Species hotspot. You don’t need to be a biologist, it has even been called to attention in several The Simpsons episodes. What if I tell you that although Invasion Ecology has become a field in itself, there is a group of respected scientists who have challenged this opinion which many easily take for granted.
On an essay submitted to Nature, one of the most prestigious science journals in the world, Biologist Mark A. Davis put this up for discussion: Species shouldn’t be judged on where they’re from, but instead from their environmental impacts, both negative and positive. It turns out that yes! Some invasive species are actually considered beneficial to their environment. Take for example tamarisk shrubs (Tamarix sp.), which were introduced from Eurasia and Africa into North America, where they were later blamed for “stealing water” and on which millions of dollars have been spent to eradicate and control with no major results. It turns out new research has cleared out the tamarisk shrub since it apparently retains the same amount of water as native vegetation. Besides, tamarisk shrubs are a preferred nesting habitat of an endangered flycatcher bird (Empidonax traillii extimus).
Without denying the pervasive effects of such invasion cases like avian malaria in Hawaii or Zebra mussels (Dreissena polymorpha) clogging pipelines in North America, Davis makes a case for a reevaluation of the idea of “invasive species = bad”. The world, Davis says, is experiencing rapid change, and it’s a naive idea to believe that ecosystems can be conserved back to a pristine original state. I agree with Davis in the sense that I have always perceived all species as invasive, perhaps except for those which supposedly originated life in the ocean smoke vents. From that point forward, all live individuals needed to slowly invade and adapt, invade and adapt. Davis points out that the view on invasive species is dated, and there’s no actual empiric evidence pointing to the equaling of invasive as bad, putting in doubt the commonly tossed around the phrase that “after habitat destruction, invasive species are the main drivers of extinction”. Native species are just as threatening to their own environments as invasives are, Davis says, citing the example of pine weevils. Davis main concern is how this prejudiced idea has lead decision makers to spend money unwisely, leading to few or none results. Sometimes, doing nothing is the best management decision.
I appreciate Davis essay for reminding us that nothing in science is completely established as truth and that what we consider to be certain at this moment, might change with further research and development of technology. However, fellow academics response was quick, and let’s just say it wasn’t positive. Davis essay was signed by 19 other scientists, Simberloff’s response was signed by 141 signatories, and it basically responds on behalf of invasion scientists, reassuring Davis and his colleagues that they do not oppose invasive species per se, but only those labeled as threatening by the Convention on Biological Diversity, and that they don’t ignore the benefits some invasive species may bring, but that they should still be weary of them and actively manage them. Simberloff finally points out that although eradication is hard, it has proven successful in some examples, particularly at the Galapagos Islands, but that’s a story for another post.
References
Davis MA (and 18 co-authors). 2011. Don’t judge species on their origins. Nature 474: 153-154
Simberloff D (and 141 co-authors). 2011. Non-natives: 141 scientists object. Nature 475: 36-37
Invaded Planet 