Through the lens of a glass house

By Razib Khan | June 8, 2011 1:15 pm

Nature has a very interesting piece up right now, Don’t judge species on their origins, which addresses the periodic bouts of hysteria which are triggered by ‘invasive species.’ I’ve addressed before the issue of biological terminology of convenience being transformed into fundamental and principled Truths. The separation between ‘artificial’ and ‘natural’ selection, or more archaically the division between ‘humankind’ and the ‘natural world.’ There are important reasons why these terms emerged the way they did, but we shouldn’t confuse the terminology for the truth. This seems definitely a problem when we humans talk about ‘invasive’ and ‘non-native’ species, as well as whether population X is worth being protected because it is a ‘species’ according to a genetic definition, or whether it is too ‘genetically polluted.’ We are after all an invasive species ourself!

Since the piece is behind a paywall I’ll extract the most relevant paragraphs:

Today’s management approaches must recognize that the natural systems of the past are changing forever thanks to drivers such as climate change, nitrogen eutrophication, increased urbanization and other land-use changes. It is time for scientists, land managers and policy-makers to ditch this preoccupation with the native–alien dichotomy and embrace more dynamic and pragmatic approaches to the conservation and management of species — approaches better suited to our fast-changing planet.

But many of the claims driving people’s perception that introduced species pose an apocalyptic threat to biodiversity are not backed by data. Take the conclusion made in a 1998 paper that invaders are the second-greatest threat to the survival of threatened or endangered species after habitat destruction. Little of the information used to support this claim involved data, as the original authors were careful to point out. Indeed, recent analyses suggest that invaders do not represent a major extinction threat to most species in most environments — predators and pathogens on islands and in lakes being the main exception. In fact, the introduction of non-native species has almost always increased the number of species in a region.

The effects of non-native species may vary with time, and species that are not causing harm now might do so in the future. But the same is true of natives, particularly in rapidly changing environments.

MORE ABOUT: Invasive Species
  • Charles Nydorf

    Defenders of biodiversity should be putting much more emphasis on habitat protection.

  • Darkseid

    no offense to Razib, as he is a cat lover, but i recently read a piece on how bad of an effect feral cats are for surrounding species. apparently, they don’t just kill birds, they also spread diseases to many other species. (don’t shoot the messenger;)

  • Razib Khan

    #2, do u own dawgs?

  • Darkseid

    no, why? I’m guessing you’ve got some dirt on them?;)

  • Vincent Vizachero

    The comment is Nature may very well be interesting, but it is also infuriatingly badly written.

    It clearly is written to malign the motives and/or intellect of ecologists with whom these authors disagree: the loaded language is too thick, and strawman arguments too numerous, to be unintentional.

    Unfortunately, as we’ve often seen in many population genetics pieces, the underlying research does not align with the characterization that Davis et al. provide. The ten sources that Davis et al. cite through endnotes are, as one might intuit, of widely variant quality.

    Generally, I’d say the data in the cited papers is of decent integrity but in almost every case the scope of the research is much, much more narrow than Davis et al. would lead us to believe.

    For example, Davis summarizes a recent paper by Gleditsch et al. this way: “In Pennsylvania, more non-native honeysuckles mean more native bird species. Also the seed dispersal of native berry-producing plants is higher in places where non-native honeysuckles are most abundant.”

    Neither of those two statements is true.

    Gleditsch found that it was the abundance of fruit-eating birds, not the number of native species which was correlated with the amount of available fruit in the landscape. Of course the study was limited to studying only frugivores, and only during a two month window designed to coincide with peak fruiting of the honeysuckles. In other words, the study was essentially rigged. It was no secret that fruit-eating birds will eat the fruit of honeysuckles (that’s one of the factors that makes the honeysuckle so invasive to begin with), and the study counted only birds most likely to benefit from honeysuckle abundance and counted them only during the time period in which honeysuckle had the greatest advantage.

    I suppose the data themselves are not wrong, per se, but they don’t begin to approach a level of comprehensiveness which would tell us whether a non-native honeysuckle monoculture is better or worse OVERALL than a native ecology. And when you ignore – as Gleditsch et al. and then Davis et al. do – the wealth of evidence that non-native plants produce FAR less insect biomass than natives do, and ignore the fact that most frugivorous adult birds were STRICTLY carnivorous baby birds once, then you end up with a most silly result.

    Consequently , when Davis et al. write things like “(c)learly, natural-resource agencies and organizations should base their management plans on sound empirical evidence and not on unfounded claims of harm caused by non-natives” it sounds more than a little bit like the pot calling the kettle black.

  • Brian Too

    Good piece.

    In recent years I have begun wondering about the characterization inherent in terms like “invasive species”.

    We all talk about evolution, adaptation, biological fitness and the like. There is a presumption that these processes are a good thing since they help perpetuate the species. However when a species enters a new territory and really makes a go of it there, we start talking about them as an “invasive species”.

    I understand that some of these “invaders” have some qualities that we could consider negative to ourselves or other species in that new territory. However is not biological success not at the root of our selfish genes? Is this not a characteristic shared by all life, only with differing degrees of achievement?

    Put it another way. Who really believes that the native species of a territory are acting on a moral basis? To voluntarily restrict their consumption of resources, so as to allow other species to flourish? Does anyone think that those native species, given a chance to evolve successful but nasty adaptive characteristics (say, poisoned throwing stars to be whimsical), would not do so?

    There was a time when stromatolites were the dominant species (maybe species isn’t the right word) on earth. There was a time when trilobites were predominant. Who is to say they weren’t the “invasive species” of their day?

  • Ian

    While they have a point, I really don’t think it’s a good article. Unfortunately, it’s difficult to explain that in a short blog comment.

    Ecology suffers from the fact that it’s an extremely difficult and complex subject that needs to be explained to the public in simple terms. And the public then needs to put pressure on politicians to act. To make matters worse, conservation is largely a grassroots endeavour – local people get together and decide that they want to save a certain species, or restore a bit of habitat.

    Then there’s the added wrinkle of environmental permitting and regulation. Undergrad (and sometimes students with an MS) are recruited by engineers (who believe that by virtue of being engineers, have mastered all other fields of knowledge) to assess the environmental impact of projects. Chances are these aren’t the people who have mastered complexity, and the people they need to explain their results to know even less about the process. So science, or what little they recall from their undergrad classes, gets dumbed down to the point where process engineers can understand it.

    Thus, we end up with “invasive species bad”.

    Davis et al. have chosen to address that level of understanding. And they have chose to get their point across through broad generalisations. These broad brush statements will, in turn, be used by the anti-enviro crowd to argue there there’s a “controversy” and we need to do away with the Endangered Species Act.

    Now they’re right that most non-native species are not a problem. It is well known to people interested in the field that the vast majority of introductions fall. Of those that succeed, few do more than persist. Of those, only a few naturalise. And of those, only a small proportion go on to be problematic. Now some (e.g., Daniel Simberloff, iirc) will argue that most problematic species go through a long latency period in which they presumably evolve the ability to become invasive. So it may be better to treat all non-natives as “guilty until proven innocent. Perhaps wise, but rather impractical. But when Davis et al. argue that non all non-native species are bad, they’re stating the obvious.

    I have plenty of other issues with the paper, but I think I’ve hit “tldr” range for a single blog comment. There’s a much better article by one of the co-authors on the paper, avialable here.

  • Randall Parker

    If humans disappear cats will do far better than dogs. Cats are better adapted to survival without us. (or so says Alan Weisman in his book about the world without us)

    But I prefer dogs.

  • Violet

    Argh! Dumping on engineers again :( .
    In most practical cases engineers have very little control over such things. It is project managers (who often have a MBA degree and not an engineering degree, to our great frustration) who does the hiring and environmental approval processing.

    I once spent two days on the design of a pipe way (of ~ 6ft) to meet environmental and fisheries department standards for the safe passage of Salmon. We understand that most things in nature don’t have an ‘yes’ or ‘no’ answer. But it’s ultimately the money that speaks if you want to do it well or rush it.

    Despite the general belief here, engineers are not the masters of the universe (sadly :) ).

  • Sandgroper

    But we should be.

  • Sandgroper

    Meanwhile, the debate still rages in Australia about whether the dingo has been there long enough to qualify as ‘native’. The environmentalist consensus is “no”. So basically, they want the world returned to the way it was several thousand years ago. I imagine they would prefer it the way it was pre-agriculture.

    I wish them luck.

    Incidentally, I think that responds to #8 – feral dogs do very well in the wild. They survive very well without humans. Of course, they do better on the margins of human settlements where they can scavenge, but they can survive just fine without that.

  • Ian

    @Violet – I have nothing against engineers, some of my best friends are engineers ;) And yes, the generalisations I am about to make are broad to the point of being wrong.

    In my experience, a project manager, at least a competent one, tends to accept that the specialists they’ve hired know their stuff. They might choose to ignore recommendations because they see them as impractical or overly expensive, but they don’t come at the conversation assuming that they know more than everyone else.

    Engineers, on the other hand, assume that they can deduce your field based on first principles. They tend to be reductionists – necessarily, I suppose, if you need to design things. Try to explain complexity to an engineer and they will, in my experience, reduce it to the two axes they learned about in an introductory biology class.

    If you write a report in clear English, a project manager is likely to be convinced. If you write clearly for an engineer, it will confirm their suspicion that you know nothing. If you write incomprehensibly dense crap, in the very best tradition of 19th century German science, then they’ll take you just a little bit seriously.

    Now, that said, engineers can be much better than grassroots environmentalists. There the problem tends to be the other way – a tendency to see things as overly interconnected, almost from a vitalist perspective. That end of the spectrum tends to attract the same people who fear GMOs. They’re the kind of fuzzy thinkers that then give ecologists and environmental scientists a bad name.

    The “environmental professionals” tend to fall somewhere between the two groups.

  • Vincent Vizachero

    Brian Too asked “(w)ho really believes that the native species of a territory are acting on a moral basis?”

    My reply is, “probably nobody”. The term “invasive species” has a widely accepted, and completely amoral, definition. The definition has two components, both of which must be met: a) the species must be introduced (i.e. be non-native) to a region in which it has naturalized; and b) the species must cause biological or economic harm in that region.

    Also, there is another point that I think that Davis et al. miss in their commentary. They recommend that we “ditch this preoccupation with the native–alien dichotomy” and focus on ecological function, yet they completely gloss over the fact that ecological function is NOT independent of origin.

    In other words, we know a lot more about the origins of most plants than we do about the complex roles they perform in ecosystems. While there are always going to be exceptions, it is entirely reasonable to presume that a species will function well within the ecosystem in which it evolved. The introduction of a species to a new ecosystem carries no presumption: it might function very well or it might function very badly. In the absence of a comprehensive analysis of the function of a particular species in particular environment, there is simply no way to know whether an introduced species will cause harm or not.

    So ecologists – and consequently policy makers and land managers – have created a very useful heuristic: use native species unless you have a compelling reason not too. This is not because ecologists stupidly assume that all non-natives are “bad”, but because ecologists wisely acknowledge that gambling with our ecosystems is unnecessarily risky.

  • Ian

    @Sandgroper – the dingo question is precisely the area where Davis et al. have their strongest point. Functionally dingoes are part of the ecosystem. The large native predators are gone, eliminated by humans, and the native fauna has evolved with dingoes (and humans) for several thousand years. So eliminating the dingo would do more harm than good. And the purists who feel they should go are the people who need to read that article. But they won’t, because the damn thing is in nature. And sadly, the journalists who read nature will spin it into something else, looking for a sensational story (INVASIVE SPECIES GOOD!)

    Instead, the people who will read it as the ecologists who (should) already understand that this is a nuanced question. But since Davis et al. have taken a rather hard line (and ignored the nuance) that will only provoke the “other side” to take a hard line and point out the obvious holes in the article.

    It would have been easy to write an article that would have done more to get ecologists on board. But too many of the people involved have made their names staking out hard line, iconoclastic positions. But at a certain point, iconoclasm turns into “you kids get off my lawn”.

  • Ian

    @Vincent #13: So ecologists – and consequently policy makers and land managers – have created a very useful heuristic: use native species unless you have a compelling reason not too.

    This is an ideal, but it rarely meshes well with reality. Reality is that the systems are overrun with non-natives. You can either do things “properly” or do them on a scale that’s large enough to make a difference. You could cut and herbicide acres of fire-savanna, or you could use non-native fire tolerant trees to reduce fuel loads over hundreds of acres. Which one is better? Well, that depends on your goal – limiting fire and reducing fuel loads, reducing erosion and siltation of rivers…or restoring natural ecosystems. The latter would be better, of course. But the larger net gain in the former makes the use of non-native species tempting. Current doctrine regarding non-native species makes it impolitic.

    There’s a discussion that needs to be had, there are costs and benefits that need to be determined on a case-by-case basis. It’s difficult when one side of the discussion has turned into a hard line position.

  • Sandgroper

    “If you write incomprehensibly dense crap, in the very best tradition of 19th century German science, then they’ll take you just a little bit seriously.”

    No I won’t.

  • Ian

    @Sandgroper – as I said, it was a generalisation that’s broad to the point of being wrong. Not all engineers are that way, not by any means. But that has been the nature of my experience.

  • Sandgroper

    You can assume that, despite being an engineer, I know a bit about dingoes too – it’s a very complex discussion, not least because of the issue of genetic purity of mainland dingoes, their role now in keeping down populations of introduced animals including feral cats, red foxes, rabbits and feral goats, and even the taxonomy of the dingo.

    Yes, they are now part of the ecosystem and it would be disastrous if they were removed from it.

    Plus I had a dingo (illegally, as they were classified as vermin, but the local cops knew her and perpetually turned a blind eye) as a companion from age 7 to 21, and I never had a better friend. After her, having a mere dog held no attraction for me, she was too brilliant an act for any domestic dog to follow.

    Having said that, Australia is an island (a bloody big one, but an island nevertheless) with unique fauna and flora, and some invasive species could be really bad news. But then they have a caveat about islands and lakes, which are just islands of water.

  • Brian Schmidt

    The article sounds like a straw man to me. If they have a better #2 threat to biodiversity than invasives, suggest it and back it up with evidence.

    And biodiversity isn’t only measured in terms of extinction. For example, non-native grasses now dominate California grasslands. Native bunchgrasses still exist but only marginally, so biodiversity suffers.

  • Pingback: Speaking of species and their origins | EcoTone

  • Isabel

    Xenophobic tendencies are at the root of the concern about “invasive” species.

    Right. And evolution is just a “theory”.

    I’m not going to read the Nature piece; it’s hardly the first time this silly trope has made the rounds.

    Which would you rather have: 1) a riparian area with a mix of native species, and perhaps some “naturalized” non-natives in the mix (as was made clear already in the comments, NOBODY cares about them- in 15 years I have run into exactly ZERO “purists” on this issue) OR 2)a riparian area where the understory is 100% English Ivy (yep, tends to take over).

    In this typical example, getting rid of the invasive ivy *increases diversity*. Does that help????

  • jay

    “If humans disappear cats will do far better than dogs. Cats are better adapted to survival without us. (or so says Alan Weisman in his book about the world without us)

    But I prefer dogs.”

    I’m not sure that’s true, though cats will do very well also. Wolves, through pack cooperation are considered second only to humans in success as predators. Wolves routinely kill prey that is faster and more powerful than they are. While domesticated, many dogs retain those instincts (indeed it is pack instincts that make them cooperative with humans) and would quite likely be successful.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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