Forecasting Worldwide Alien Invasions

Image Credit: Bernard Dupont, CC BY-SA 2.0, Image Cropped

Projecting the continental accumulation of alien species through to 2050 (2020) Seebens at al., Global Change Biology, DOI: 10.1111/gcb.15333

The Crux

A by-product of globalisation is that over the coming decades, no matter how many episodes of Border Patrol get recorded, new species are going to find their way into new habitats and potentially become invasive alien species, exerting negative effects on the locals. We’ve seen this in the past, and I’ve beaten many a dead horse writing about these species on this site.

What this paper set out to find is whether or not we can predict at what scale this trend will increase.

What They Did?

The authors used the Alien Species First Records database, which is a database containing the first known records of an alien species in a new area. It’s in the title really. They created ‘candidate pools’, basically a number of candidate species which could invade a region, based on invasions that happened up until the year 2005. They used this to estimate the rate of new invasive species arrivals up until 2050.

The records were broken into seven major species groups, and then further into eight continents, with Temperate and Tropical Asia divided into separate continents, and the Pacific Islands also forming a separate continent (Antarctica was excluded).

The models were also backcasted. This means that their predictions were tested based on 1950 data, to see how their model’s predictions for 2005 stack up against how many invasions had actually taken place by 2005.

What They Found

When you’ve got seven different species groups over eight continents, it’s a fair bit that your model isn’t going to work perfectly for all of them. The models here for invasive mammals and birds weren’t exactly convincing, but across other species the model performed reasonably well.

According the the paper’s projections, arthropods and vascular plants have been and will continue to be the most frequent invasive species in most continents, though it seems they may soon reach saturation (ie. all those that can invade will have invaded) in a few continents. Europe and South America look like they will be particularly hard hit by invasive species over the coming decades. You can check out a visual summary of more trends below.

Past and predicted invasion trends across seven species groups and eight continents. Shaded polygons represent uncertainty in trends. (Image Credit: Seebens et al., 2020)


I get that with a model like this, you have to allow a lot of flexibility, as you’re working with pretty basic data data. All you have to predict future invasions are species names and dates. However a lot of the modelling here feels like a “let’s just see what sticks” approach. Again, I understand why it’s the approach that’s been used. But it makes me question how informative this model really is. Then again, this model is not so much an applied tool as a reminder of the biodiversity upheaval we’re likely to see in the coming decades.

So What?

We know that biological invasions are going to continue, and this paper suggests that most types aren’t slowing down any time soon. Tough decisions have to be made here. Do we see the change in our ecosystems as a necessary by-product of our expansion, or do we step in and preserve what ‘natural’ ecosystems we can? Personally, I think we have a responsibility to at least ensure some regions remain as stable as possible, but as species invasions increase, the resources required to do that may become exhausted.

Speaking of exhausted, Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology . You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

One comment

  • Sam,

    Not a ay goes by I don’t see a new invasive down here in Nuevo Macondo. This past year it’s been a new snail pest, the Indian horntail snail (Macrochlamys indica) with its precious freight of rat lungworm, just as we were getting the African giant snail invasion under control. This probably means another prodigious waste of beer, even if styrofoam bowls sunk in the garden soil aren’t that expensive.
    On the brighter side, there seem to have been a couple of new, reasonably colorful anoles (Anolis ssp) out in the yard, about the usual size but a tad more aggressive and territorial. With 425 species, some of which you can only distinguish by counting the number of plates on their heads or checking the patterns on their dewlaps, it might take me a while to key them out. And this is south Florida, which is notoriously anole retentive.
    I’ve also seen at least two species of spiny iguana out here, the Mexican black and the Yucatan spiny tailed iguana. Kiss my hibiscus goodbye. They match up nicely with the local tegu population – golden tegus, black and white tegus, silver tegus, red tegus, green tegus – which seem to be hybridizing merrily out there, to boot. And of course we’re seeing various curlytail as well as ameiva species. Pythons, did you ask? Oh. On top of all this American alligators seem to be following global warming – not many Republicans among them, I guess – and showing up in the suburbs of Richmond, Virginia (they’re already old news in Newport News).
    So if you want to start plotting alien expansion, this is a good place to start. My yard is available for camping out by graduate students who are a bit less histrionic than that poor American doctoral student studying marsupial mice in that nonpareil film “Cane Toads.”
    So if you want to start plotting


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