Are invasive species bad? Also “Long live the weeds”, by Theodore Roethke

I’ve attended a lot of conferences this autumn (3 down, 2 to go!). When I registered for all these conferences, I didn’t have a job lined up for next year, so I was feeling a little desperate. Now that I have a job lined up, I just get to enjoy everyone’s amazing research. Seriously…if you think about how much work goes into every talk and poster, and then multiply it by the number of talks and posters, it’s actually mind-boggling how much work these conferences represent.

Anyway, I spent a week at an invasion biology conference and one of the ongoing debates I find especially interesting is the dichotomy between the ecologists focused on eradication of invasives and quantifying their negative impacts (with the perspective or underlying assumption that they are purely bad) vs the ecologists who are starting to explore the potential beneficial aspects of species invasion and the implications. There almost seemed to be a gulf between these two groups, at least at this conference. Someone would give a talk about potential benefits of an invasive species, and would get some snarky questions on whether it’s even possible for invasive species to have benefits, or whether they are by definition negative.

Obviously, you can quibble about definitions, but that is just boring (to me). Invasive, non-native, alien, resident, naturalised, weed…all of these words can be bandied about, but what I’m really interested in is the *inherent* underlying assumption of the scientist.

Is it possible that this underlying assumption inherently biases the outcomes of our studies? After all, all species probably have mutualistic interactions (it’s probably hard to survive without *some* mutualists), which could be labeled as a “positive” interaction. Then again, it’s also impossible to exist without negative interactions! Even the most innocuous plant competes with others for limited resources, right? I’ve discussed species with two faces on here before…

Naturally, if you’re looking for the negative impacts of an invader, you look for a negative interaction: competition, predation, pathogens…and if you’re looking for the benefits of an invader, you look for positive interactions: pollination, ecosystem services, biodiversity…

I first became interested in invasive species in college, when I decided I would read all of the “classics” of ecology, and the first book I read was Charles Elton’s 1958 “The Ecology of Invasions by Animals and Plants”, basically a handbook of all the negative impacts invasive species have. I started volunteering for invasive plant removal days.

I remember one day in particular where I, with 8 other people, spent 8 hours clearing a patch of forest of Garlic Mustard, stuffing it into black bags so that the seeds wouldn’t survive to disperse. At the end of the day, I looked up beyond the boundary of the area we cleared, and saw a sea of green Garlic Mustard waving gently in a breeze. In that moment, I thought maybe our approach, which I nicknamed “Brute Force and Ignorance”, would not be that effective.

When I started grad school, I set out to study the impacts of invasive species, Charles Elton’s book fresh in my mind. But for the first literature review I performed on invasive species impacts, I stumbled on this paper by Sax and Gaines (2003). Invasive species don’t necessarily decrease species richness, it argued, sometimes they increase species richness!

Indeed, the harder I tried to build an argument about how invasive species are universally bad, the more exceptions to the rule I found. Our lab was focused on an invasive thistle, and I went to the field to study its impacts on the insect community. I was totally naive and had no previous experience with insects, but even I could see that this invasive species was absolutely crawling with insects. In fact, they absolutely loved it!

Over the course of the next few years, my research only reinforced the idea that this invasive weed was actually a huge benefit for pollinators in agricultural systems, where very few native species could withstand the agricultural intensity (plus, bees love thistles).

So it’s interesting to see other ecologists on this journey of exploration from the perspective of invasives being all negative, to becoming curious about their positive impacts as well. I have a friend who tells me that the whole field of “invasion biology” is bogus, but I think that’s extreme. We’ve learned a lot from studying invasive species after all!

But I think we need a more nuanced perspective before deciding whether a species is “good” or “bad”, and before using its original range as a label that automatically makes it look like a problem. I’ve seen some strange behaviours, almost to the level of obsession, regarding the eradication of species that probably can never truly be eradicated (eg our garlic mustard). There’s a story I’ve heard a number of times of an Australian bay (Cullen Bay) where an invasive mussel was detected in 1999. The government activated an emergency response and dumped “187 tonnes of liquid sodium hypochlorite and 7.5 tonnes of copper sulphate…to the three marinas over two weeks.” sauce

The first time I heard this story (which is usually told as a way to show how effective rapid response can be in preventing invasion), I thought it was an impresive and effective display. But the more I hear about it, the more I wonder if it is a harsh reaction to what may ultimately be an inevitable invasion anyway…after all those chemicals didn’t *just* kill the invasive species. They killed everything in the bay. And yes, the native species can recolonize, but what if they were already holding on by a thread, hit hard by nutrient runoff, pathogens, and climate change? Black striped mussels are one of those species considered to have pretty much exclusively negative impacts, both from economic and ecological perspectives. But…our world is changing and sometimes I wonder if our illusion of control over it leads to more problems than it solves.

Maybe the differing perspectives voiced at this conference are the best thing that could happen…the absence of consensus drives science to be more rigorous, more complete. I certainly don’t know the answer to all this, but I think it’s worthwhile for us all to try and see the other perspective.

Long Live the Weeds

Long live the weeds that overwhelm

My narrow vegetable realm! –

The bitter rock, the barren soil

That force the son of man to toil;

All things unholy, marked by curse,

The ugly of the universe.

The rough, the wicked and the wild

That keep the spirit undefiled.

With these I match my little wit

And earn the right to stand or sit,

Hope, look, create, or drink and die:

These shape the creature that is I.

– Theodore Roethke

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16 thoughts on “Are invasive species bad? Also “Long live the weeds”, by Theodore Roethke

  1. Garlic mustard, Japanese stiltgrass, mile-a-minute vine, mugwort, climbing euonymus, Asian stinkbugs, Japanese beetles, spotted lanternflies…these are a few of my least favorite things. But I recognize how much of the flora and fauna around me are not “native” (though some have been here in the USA for over 500 years, like broadleaf plantain). Your point about mutualism is well-observed! At this point, there’s probably no stopping globalism. Maybe the discussion should be changed…

  2. A fascinating post. It is a tough one.
    Take Japanese knotweed for example. It is probably impossible to eradicate, and we can probably only control it’s spread. And when you do control, the most effective chemical appears to be glyphosate. So what do you do?? If left uncontrolled you could end up with places like the Rhonda Valley in Wales where it covers acres of land. And then there is the cost. It’s really a difficult issue.

  3. It’s interesting. After all us humans are an invasive species ourselves in a way. We probably cause far more harm to the environment than any invasive mussel!

    With the Asian hornet, I know a few people see it as a beautiful creature which they want to see come to the UK and think beekeepers are doing more harm than good by putting up monitoring traps and trying to keep it out.

  4. “Brute Force & Ignorance”? My personal motto… ps I get your point but aggressive invasive animal / bird / fish species undoubtedly do adversely affect native species eg parasitic nesting birds, lionfish in the wrong ocean, & co

    • Yes, they do, but do they do so more than native species affect more than one another and do the management options do more harm than good and is management sustainable and will the eradication efforts be effective/permanent? More questions than answers

      • Good Qs! Main trouble is, by the time people have (a) noticed the problem (b) formed a committee and working parties (c) reached a consensus how to tackle it (d) initiated an action plan and (e) started implementing it… it’s too late. The novelty shiny cowbird influx has already decimated the local yellow warbler population. But maybe invasives are more of a threat on islands? (And don’t get me stared on eg grey v red squirrels / evil-yet-fluffy animal activism etc) 🐿

      • Yes, invasives definitely have been shown to actually cause extinctions on islands, while not so much on main lands (humans excepted), but again the solution is not obvious. I feel like we’re going to be permanently stuck trying to eradicate every new species that shows up, and yet, it’s impossible to prevent new arrivals.

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