Alien Invasions: Do They Deserve Their Bad Rep?

Recently, in a post titled "Ecologists: Time to End Invasive-Species Persecution", Brandon Keim discussed a comment published in Nature which argued that the ecological community unfairly vilifies the various plants and animals we've transported around the globe. In some sense, the authors are right, at least as far as saying that not all alien species should be considered bad or needing removal.

Straight from the beginning, though, the authors attack a dichotomy that doesn't exist. They write that a "native-versus-alien species dichotomy" is counterproductive, and that new, pragmatic approaches are needed. This makes it sound like scientists and managers label every plant or animal as A or B, and those in A are allowed to stay and those in B are eradicated. To an ecologist, though, there is no "dichotomy" - there are a range of labels that apply to a variety of situations. Specifically, there is already a strong distinction between invasive species and introduced, non-native or alien species - not to mention game species, fisheries species, etc.

I don't know of a single removal program that seeks to eradicate every species in an area that wasn't there 100 years ago. Removal programs don't target all "non-natives" - they target invasives.

Invasive species get their own category, as well they should. They are specifically defined by the US government as "alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health." Almost half of the threatened and endangered species are at risk due to the impacts of invasive species. In the US alone, invasive species cause an estimated $140 billion dollars in environmental damages and losses every year1.

Take the species I study: lionfish (Pterois volitans and P. miles). Lionfish were first sighted in the Atlantic in the late 1990s. In the past decade, they have become ubiquitous from Brazil to New York. They're a classic invasive species: they grow quickly, breed year round, have no natural predators or diseases in their invasive range, and they are causing serious ecological damage. Studies have found they reduce the recruitment of larval fishes by 79% on average2, and they are causing a shift from coral dominated to algal dominated ecosystems3. The lionfish hardly stand alone. Hundreds of species from rats and mice to cane toads cause serious damage to ecosystems on a daily basis.

So do we over-vilify invasive species? No, we don't.

The debate about invasive species really hits home in Hawaii, where 25% (maybe more) of the local flora and fauna aren't just native, they're endemic, which means they are found nowhere else in the world. It's estimated that somewhere around 25 new species are introduced to Hawaii every year, but thankfully, most of these do not become invasive. Indeed, of the 13,000 or so species of plants that have been introduced to Hawaii, only about 1% are considered invasive. Those that are deserve the title and the removal efforts that tend to go with it. When invasive species take over natural habitats in Hawaii, they very directly and quickly drive species towards extinction. Not surprisingly, Hawaii has a number of invasive species removal programs targeting species that are or might be a problem.

i-223203fd49f2659c642391255fd3bbd6-davis_nature_paper_miconia-thumb-250x248-66158.pngI couldn't believe the authors chose to picture Miconia (Miconia calvescens) removal in Hawaii as their lead image, especially since they then didn't even bother to talk about it. Yes, a lot of effort is spent preventing the spread of Miconia in Hawaii, but it's for damn good reason - all Hawaiian biologists and managers need to do is take a look at Tahiti, where it's referred to as "green cancer". A single Miconia was introduced to Tahiti in 1937. Within a half a century, the plant took over. By the 1990s, the plant had spread to 70% of the island's forested areas, over a third of which were near monotypic, meaning the Miconia had out-competed and overrun all the other native species of trees4.

On Oahu, Miconia has not had that kind of impact because we have actively prevented it. If we were to stop these removal efforts, there is little doubt that Miconia would spread. One study estimated that it would take less than a century for Micona to take over Oahu like is has Tahiti5. That study also estimated what would happen if we stopped control efforts for the next 40 years; the cost of doing nothing, based on loss of native habitat and species, changes in watershed properties, and other ecosystem damages would be $627 million.

This is the species that Davis and his colleagues chose as the front image for saying we unnecessarily persecute non-native species?

But, of course, the authors don't talk about Miconia, or any of the removal programs in Hawaii. They instead cherry-pick their examples, cite their own work, and ignore the vast majority of the science from the past ten years which supports invasive species management.

I wouldn't be so bothered by this short essay, except that more than ever, management programs need to be supported. If only the authors' claim that there is "a pervasive bias against alien species that has been embraced by the public, conservationists, land managers and policy-makers" were true. But sadly, many politicians and people just don't care. Just earlier today, my grandfather was watching a Fox News segment called "The Money Hole", in which John Stossel started ranting and raving about all the ways in which the US wastes tax payer money. One of his examples? The $500,000 spent on removing brown tree snakes from Guam - one of the nastiest invasive species around, responsible for the extinction of ten out of the twelve native bird species that once lived there as well as a slew of other damages.

I'm actually shocked this paper was published by Nature. I'm even more shocked such an essay wasn't peer-reviewed and the authors were paid for it. Of course, I generally would find it hard to trust an essay where the vast majority of the cited papers are written by the coauthors, and those that aren't are outdated by a decade. How can they deride the management plans currently in use when they don't actually evaluate the current efforts?

By dishing out blanket criticisms towards all invasive management programs, the authors provide fuel to the fire of those who attack environmental work on a daily basis. Conservation programs and scientific agencies which study the practicality, necessity, and effectiveness of them are already first on the chopping block when budgets are cut. They're struggling for funding in these harsh economic times, and articles like this one only seek to unfairly undermine their credibility when they need it most.

Comment in Question: Davis, M., Chew, M., Hobbs, R., Lugo, A., Ewel, J., Vermeij, G., Brown, J., Rosenzweig, M., Gardener, M., Carroll, S., Thompson, K., Pickett, S., Stromberg, J., Tredici, P., Suding, K., Ehrenfeld, J., Philip Grime, J., Mascaro, J., & Briggs, J. (2011). Don't judge species on their origins Nature, 474 (7350), 153-154 DOI: 10.1038/474153a

PIMENTEL, D., ZUNIGA, R., & MORRISON, D. (2004). Update on the environmental and economic costs associated with alien-invasive species in the United States Ecological Economics DOI: 10.1016/j.ecolecon.2004.10.002
2.Albins, M., & Hixon, M. (2008). Invasive Indo-Pacific lionfish Pterois volitans reduce recruitment of Atlantic coral-reef fishes Marine Ecology Progress Series, 367, 233-238 DOI: 10.3354/meps07620
3. Lesser, M., & Slattery, M. (2011). Phase shift to algal dominated communities at mesophotic depths associated with lionfish (Pterois volitans) invasion on a Bahamian coral reef Biological Invasions DOI: 10.1007/s10530-011-0005-z
4. Meyer, J., & Florence, J. (1996). Tahiti's native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae) Journal of Biogeography, 23 (6), 775-781 DOI: 10.1111/j.1365-2699.1996.tb00038.x
5. Kimberly M. Burnett, Brooks A Kaiser, & James Roumasset (2007). Invasive Species Control over Space and Time: Miconia calvescens on Oahu, Hawaii Journal of Agricultural and Applied Economics,, 39

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Straight from the beginning, though, the authors attack a dichotomy that doesn't exist.

Yes, indeed, it's a classic strawman approach. Great post, I have nothing to add other than to agree.

"I'm actually shocked this paper was published by Nature."

Me too. Thanks for writing this post about it.

Alas, Hawaii is about as likely to limit the spread of the coqui as Texas is to limit the spread of giant cane. They had better get used to its call.

I used to favorable opinions of non-natives coming mostly from folks in Europe, where the problem is not costing as many billions, and the woods are not ghastly with invasives, so I was surprised that many of the authors were from North America.
I volunteer for the state (MI) fighting invasives, so it's personal. I invite the authors to come see honeysuckle invasions and we can compare rare native plant densities. Traveling through it will be a battle though. Did some species benefit - I'm sure we could find an example or two (and write a paper), but that doesn't make it good overall.

In addition to being an ecological blight, the brown tree snakes of Guam have picked up the nasty habit of attacking babies in cribs. I guess Stossel forgot his usual script of how environmentalists want people to die.

I appreciate this response to the paper in Nature--and do agree that the impact of these species is devastating, especially in places like Hawaii. I think we need a significant funding of strong habitat rehab programs. However, I have a beef with the use of the term invasive for ethical and semantic reasons. When we label other species invasive part of what happens is that we effectively remove ourselves as players in the ecosystem and eliminate our ethical responsibility for the poor state of the invaded habitat. We, of course, are the ultimate invasive species, but it's easier to blame the other species that we transported to the new habitat. If a rehab project is done with clear recognition of the proportional impact of anthropogenic forces like habitat destruction and fragmentation versus introduced species it can be very effective but so often developers are allowed to destroy huge swaths of land in exchange for remediation that involves eliminating an invasive species with an impact much less damaging than the habitat destruction itself.

When we label other species invasive part of what happens is that we effectively remove ourselves as players in the ecosystem

I have a hard time understanding this since it's well-understood that we're the species importing the invasive in the first place ...

"so often developers are allowed to destroy huge swaths of land in exchange for remediation that involves eliminating an invasive species with an impact much less damaging than the habitat destruction itself."

If that's true, it's an outrage for sure. Is it true? Citation plz.

By CS Shelton (not verified) on 14 Jun 2011 #permalink

You state the authors of the essay âdish out blanket criticismsâ towards all invasive management programs. This simply is not correct. The very first sentence of the piece published in Nature states that âConservationists should assess organisms on environmental impact rather than on whether they are natives.â There is no blanket criticism of invasive management programs â there is a call to base such decisions on good data. The authors of the article are not alone in expressing a desire to see policy decisions based on good science. Add Keller, Lodge, Lewis, Shogren, editors of âBioeconomics of Invasive Species: Integrating Ecology, Economics, Policy, and Management,â (Oxford University Press, 2009), and Hoagland and Jin (resource economists at the Marine Policy Center, Woods Hole Oceanographic Institution) (2006) to the list.

In fact, your first citation is a good example of the problem with poor science. The Pimentel et al. 2004 [sic] report is rife with errors. Hoagland and Jin (2006: âScience and Economics in the Management of an Invasive Species,â BioScience 56(11): 931-935) point out that Pimentelâs estimates of the economic impact of the green crab were used to help justify public policy â yet the data published was âtaken from the wrong geographic location,â thus âprediction of ecological effects appear to rest on loose footing,â and âeconomic methods [were] misapplied in constructing the estimate.â

The article by Davis et al. published in Nature clearly does not, as you say, âseek to unfairly undermineâ the credibility of âconservation programs and scientific agencies which study the practicality, necessity, and effectiveness of [invasive management programs.â It merely calls for such programs to base policy on sound science and economics, not value judgments.


I respectfully disagree. The very statement you quote implies that currently, managers don't assess organisms in this manner, which is simply untrue. There are no campaigns to eradicate the wallabies on Oahu, for example, because they aren't an ecological problem. Furthermore, the authors state very clearly that "we urge conservationists and land managers to organize priorities around whether species are producing benefits or harm to biodiversity, human health, ecological services and economies" - implying, again, that this is not what is currently being done. Is it really the author's belief that managers knowingly base their efforts on unsound, non-empirical evidence? Do we, as scientists, not provide such information? Of course we do, and the managers take this information and use it to inform their decisions. After all, the very definition of an invasive species is one which has these negative effects.

Managers and scientists make the best policy decisions based on the information available. It sounds like the authors would rather have us wait 20 years after every introduction to get 'sound empirical evidence' as to whether the species will really be a problem. For fragile ecosystems like those in the Hawaiian islands, this kind of wait and see attitude will certainly lead to devastation. If we wait to let a species that has the potential to be highly invasive get its footing, we'll never be able to get rid of it. If we want to preserve the endemic species here, we have to be proactive, targeting any species that has been a problem elsewhere or has the characteristics of an invasive species.

Whether the comment seeks to undermine these programs or not, it does, in the same way that New Scientist publishing a magazine with the cover "Darwin Was Wrong" bolsters creationist platforms. Politicians aren't going to take the time to read all of the science for the species in their area and determine if the invasive species they're paying to remove are the really bad ones - they're going to take an article like this and use it to justify cutting or redistributing funds away from these management programs, saying "see, even scientists say that most invasives aren't really that bad".

Yes, we can always improve our science. We can do better studies which more accurately portray the interactions and effects of different species in different environments before we remove a single one. And, while we carefully examine all the details, species like Miconia will drive species to extinction. But hey, at least we'll have documented it very, very well.

Christie, yes, managers and policy makers make decisions based on the information available, and scientists provide that information. Obviously, I canât speak for the authors, but it seems to me that after 20-30 years of numerous eradication efforts, the point is that itâs time to take a step back and review what weâve learned from those projects. We now have a very large and growing body of âsound empirical evidenceâ that points to a different conclusion in many instances than was first believed at the time those decisions were made. Letâs be honest: the approach to invasives has been "what do we kill next," and as it's turning out, data now available indicates that many of these efforts have proven either unnecessary, futile, or had unanticipated consequences that ended up further endangering the species the eradication efforts attempted to protect. Unfortunately, science sometimes IS driven by bias, whether intentional or not. But that is what I take away from the position of the Nature article: our definition of âinvasiveâ needs revision and how we approach species management needs review.


Are you an ecologist? Are you aware that the "conservationists and ecologists are xenophobes in disguise (or at least driven ignorantly and subconsciously by xenophobia)' meme makes the rounds pretty regularly? Or that ecologists and other scientists have been discussing the issues you and the authors of the condescending Nature article bring up quite extensively for years? Unfortunately, in the field of conservation we don't have the luxury of waiting decades for every result. Things are happening fast in real time.

You are correct though, that neither invasive species nor climate change can compare to the threat of habitat loss. In fact, the habit loss is what makes so many species unable to cope with the other two threats. In effect, they have no escape. But it doesn't mean all three issues are not of vital importance.

"But that is what I take away from the position of the Nature article: our definition of âinvasiveâ needs revision"

You seemed to have missed Christie's point, which is that the Nature article did not accurately define the term and the relevant issues. As is often the case they erected a straw man. No one thinks that way (all non-natives must be destroyed). So what exactly needs revising? The only think accomplished by that piece is it makes conservation more difficult.

Obviously this is a vast topic and the issue is also extremely complex, so it cannot be covered in a comment section. Books have been written about it. What I want to point out is that so many eradication projects have either gone wrong or it has taken a very long time to eradicate the species. And these examples are mainly on islands. Imagine if we undertake these eradication projects on continents, which is often suggested by environmental groups.
A few examples: On Marion Island (located in the sub-Antarctic Indian Ocean), it took 19 years to eradicate around 2,500 catsâscientists aerial-sprayed the feline distemper virus over the island---35% of the cats survived the virus and started breeding back to the same numbers as before. For the next dozen years they tried poisoning, intensive hunting, trapping, and dogs. This on an island that's only 115 square miles in total area, barren, and uninhabited. The cost, I'm sure, was astronomical.

In 2007 the New York Times reported on the Northern pike issues in California: âThe poison did not work and neither did the hook and bobber. The electrical probes were somewhat effective, but do not even ask about the explosives. For the last decade, the state of California has waged a Sisyphean battle against the northern pike, a fish and a voracious eating machine. In the mid-1990s, when pike were first found in Lake Davis, a Sierra Nevada reservoir about four miles, or six kilometers, north of here, the discovery set off a panic over the potential effect on the local trout-fishing and tourist industries as well as the possibility of the fish migrating to fragile ecosystems downstream. Since then, millions of dollars and thousands of man-hours have been spent trying to spike the pike.â But while the methods, including poison, electro-fishing, explosives and decidedly low-tech nets, have varied, the results have remained the same.
"We've taken 65,000 pike out of the lake," said Steve Martarano, a spokesman for the California Department of Fish and Game. "And we haven't made a dent."
"This is a top-of-the-line predator," said Ed Pert, the project manager. "If we don't get it this time, we may need to rethink things."
Then we have the plan to eliminate the felines from Macquarie island which allowed the rabbit population to explode and, they in turn, destroyed much of the fragile vegetation that birds depended on for cover.
Removing the cats from Macquarie "caused environmental devastation" that will cost authorities 24 million Australian dollars ($16.2 million) to remedy, Dana Bergstrom of the Australian Antarctic Division and her colleagues wrote in the British Ecological Society's Journal of Applied Ecology.
Other failed eradication programs:
*On Amsterdam Island in the Indian Ocean, biologists eradicated the feral cats to protect the ground-nesting seabirds. The black rat and house mice population immediately increased, as their main predator was removed, and they began to prey upon the ground-nesting birds.
*In New Zealand biologists poisoned the rat population; the stoats, which mainly preyed upon the rats, shifted their diet from rats to the endangered birds.
I do think, at the very least, scientists have to re-think their plans for eradicating feral/alien/introduced/exotic mammals. Nonlethal control does exist. This allows the ecosystems to adjust. Catch-and-kill seems like a quick-fix. But this is exactly what is it, without any long-term benefits.
There are more examples but I wish to end with a quote from Roger Tory Petersen: âMost thought-provoking of all is to discover the balance of nature; the balance of a bird and itâs environmentâ¦that predation harvests only a surplus that otherwise would be leveled off in some different way; hence putting up fences and shooting all the hawks and cats will not raise the number of Red-eyes Vireos to any significant degree.â

I must take issue with the claim that âIn the US alone, invasive species cause an estimated $140 billion dollars in environmental damages and losses every year.â Indeed, youâre actually undermining your own credibility by citing the work of David Pimentel on this point.

In their 2006 BioScience article, Porter Hoagland and Di Jin, resource economists at the Marine Policy Center, Woods Hole Oceanographic Institution, take Pimentel and his colleagues to task for their sloppy work. Focusing on the economic impact of the green crab, as estimated by Pimentel et al. ($44 million per year), to make their point, Hoagland and Jin warn: âThere are many reasons to be concerned about the use of these estimates for policymaking.â (Hoagland & Jin, 2006)

Among their concerns, are the use of potential rather than actual impacts, and the validity of the underlying scienceâas well as the overall lack of rigor involved in developing such estimates: âHeretofore, estimates of the economic losses arising from invasive species have been far too casual. Unfounded calculations of economic damages lacking a solid demonstration of ecological effects are misleading and wasteful.â (Hoagland & Jin, 2006)

In fact, such estimates can do damage of their own. As was the case last year when authors of âFeral Cats and Their Management,â published by the University of Nebraska-Lincoln, claimed that âpredation by cats on birds has an economic impact of more than $17 billion per year in the U.S.,â citing as their source the very same Pimentel paper youâve cited.

According to Pimentelâs bizarre form of accounting, hunters value an individual bird more than 500 times as much as a birdwatcher doesâsuggesting, it seems, that dead birds are far more valuable than live birds. (Readers interested in learning more about just how flawed this "estimate" is ought to read Laurie Goldstein's critique, â17 Reasons the Economic Impact of the Domestic Cat as a Non-Native Species in the U.S. Does Not Cost $17 Billion.â)

Nevertheless, that $17B figure made headlines around the world for months (as recently as last week ). The National Audubon Society and American Bird Conservancy, among others, were more than willing to overlook the UNL paperâs inexcusable lack of rigor (and equally inexcusable excess of bias) in exchange for its sensational âestimateââanything to perpetuate the shameless witch hunt against what is perhaps the most persecuted of âinvasive speciesâ: the domestic cat.

While I appreciate the discussion of non-native/alien/invasive species, you do your readers a disservice by referring to Pimentelâs work as if itâs credible.

Peter J. Wolf
Vox Felina

*In New Zealand biologists poisoned the rat population; the stoats, which mainly preyed upon the rats, shifted their diet from rats to the endangered birds.

Could we have a citation for this please? I've followed eradication programs in NZ for a while and I've never heard of a program that does not aim for eradication of all mammalian predators that are dangerous to local wildlife. The work of DOC against stoats, cats, rats, etc forms part of an integrated management strategy. I would be very surprised if this comes from any recent work in NZ.

Around 70% of crop production in South America and also Africa is from introduced crops and not from native crops. It seems that crops do better far away from their co-evolved pests and diseases. There is a great deal that can be learnt by evolutionary biologists by studying introduced species and, when they become invasive, the ways in which they are superior to endemic species.
If the ecosystem service of food provision is better supplied by introduced rather than native crops, then so too may be other important ecosystem services (carbon capture, flood prevention, water treatment and lots more). As invasive species are obviously superior to native species in some way the rarity or endemicity of native species should not be a factor in an economic assessment of supposed `damage' caused by alien species. Wait and see might be the best option, rather than knee-jerk elimination.

By Dave Wood (not verified) on 05 Jul 2011 #permalink

"where 25% (maybe more) of the local flora and fauna aren't just native, they're endemic, which means they are found nowhere else in the world." Wow I had no idea it was so high. That's a huge amount for such a small area.

"Around 70% of crop production in South America and also Africa is from introduced crops and not from native crops." Good point.

if they are good then what edvidence do you have of that