I originally started writing this post two years ago, back when Donald Trump had just been elected as President of the USA. I didn’t finished writing it then because I assumed that the topic was just a passing fad, something none of us actually took seriously. Fast-forward to today, the US government has been shut down for more than three weeks as Trump tries to hold the country hostage over his border wall with Mexico. I suppose now is a as good a time to finally publish this post, even though a paper was published on the topic in BioScience last year.

As one of the most absurd campaign promises in recent history, Donald Trump’s commitment to building a wall between the United State and Mexico has attracted many critics. Many scoffed at his claims that such a structure will keep out the make-believe mob of bad hombres chomping at the bit to sell drugs to innocent Americans. Others giggled at Trump’s conviction that those very same bad hombres would pay for his trademark erection.

But this post is not about the fragile justification for building a massive wall. It’s a thought experiment on how many species would be affected by this cross-continent barrier.

We know that fragmenting species’ ranges can have terrible ecological consequences. Migratory routes get cut-off and once-suitable habitats become inaccessible. Modern conservation technology means that is surprisingly easy to get a rough estimate of how many species might be affected by such a wall. Here’s how I did it:

I downloaded global spatial data of the geographic distributions of all amphibians, reptile and mammals from the IUCN Red List database (Although it is possible, I didn’t include data for birds because the spatial data is hosted by BirdLife International and is stored in an inconvenient format where each family is a separate dataset… also, most birds could just fly over the wall).

I then extracted the subset of all species ranges that intersected the US-Mexico border.

Finally, I used the letsR package in R to download all the information on the conservation status of species that might be affected by the border wall. (This step could also be done manually from the IUCN Red List website, but letsR provides a convenient shortcut).

Overall, 350 species of amphibians (49 species total: 1 Near Threatened, 2 Vulnerable, 2 Endangered), reptiles (145 species total: 5 Near Threatened, 1 Vulnerable) and mammals (156 species total: 6 Near Threatened, 1 Vulnerable, 2 Endangered) could potentially be affected by Trump’s wall. 94% of these species are in the lowest category of extinction risk, Least Concern, which means that 6%, or 21 species, have already been flagged as being of some for of risk to extinction. A wall would just exacerbate this risk.

You can access all the species data here if you’d like to do some of your own sleuthing.

Of course, not every one of these species will necessarily be harmed by the giant wall. However, there are certainly many other plant, bird and invertebrate species not included here that could be harmed instead. So, while this humble blog post is by no means authoritative on the conservation impacts of building a massive wall between two countries, it does show that the consequences are certainly not trivial.

Building a wall between the United States and Mexico carries considerable risk to species survival. To be more specific, building a wall carries at least 350 small risks, because this is the number of species that might be affected. 350 species is not a number to sniff at, but, hey, this won’t be a problem should the Trump administration succeed in deregulating species conservation.