Unintended consequences of the amphibian trade
Why small actions can have worldwide consequences
Every so often something you read just gets under your skin, injecting a meme that you can’t just ignore. That’s what happened when I read “Lessons of the Lost” by Joseph R. Mendelson, in American Scientist (v 99, p 438-441, 2011).
When I picked it up as weekend reading, I thought I was just going to read a bit about how amphibians are mysteriously disappearing worldwide. Indeed, that’s what the article is about. But as a piece of science writing, it’s masterful, and chilling. “I chose to become a herpetologist, not a paleontologist, because I enjoy working afield with live animals. Recent reflection has forced me to reconsider my academic title. I am a forensic taxonomist.”
The article is about, as I expected, world-wide frog death.
Mountain yellow-legged frogs (Rana muscosa) killed by chytridiomycosis in August 2008.
(Sixty Lake Basin in the Sierras)
But he has some data; he can name names and point fingers. The culprit seems to be amphibian chytridiomycosis, a disease caused by the fungus Batrachochytrium dendrobatidis. (The name is from the Greek words batracho (frog) and chytr (earthen pot), while the specific epithet is derived from the genus of frogs from which the original confirmation of pathogenicity was made (Dendrobates).) The disease and fungus have no common names, they’re not familiar or even especially visible in the way that a similar disease among mammals, “white nose syndrome” (caused by the fungus Geomyces destructans) is currently devastating populations of bats in the US.
Why did this article get so much under my skin? Mostly because, as I said, Mendelson is a great writer, but also because his message is summarized in a few nuggets that persist in memory and rattle around alarmingly in my brain. As he says: “The concept of ‘endangered species’ does not apply here. We are witnessing the nearly complete elimination of clades of species.”
That phrase scares the bejesus out of me: “... the nearly complete elimination of clades of species.”
A clade, you have to understand, is a species and all of its relatives, both currently living and extinct—think of all crocodiles, or all dolphins--those are clades. “Clade extinctions” are massive, major, damaging events—the kind of thing that happens when asteroids strike the earth. As Mendelson says, “…we were all trained that such things are only to be observed in the fossil record. This precedent from the amphibians forces us to address the serious implications for possible disease-driven losses among other major clades. Consider for a moment the potential consequences among [the clades of] monocot plants (corn, wheat, rice), pollinating insects, salmonids, or scombrid fishes (mackerel, tuna), mammals or birds.”
How does a relatively obscure fungal disease get shared globally? Sadly, as a side-effect of global trade. The timing and spread of the disease makes it seem that the vectors of transmission were likely amphibians exported for food, hiding in trade goods, researchers, or by careless and unknowing collectors. This is an unintended accident of the worldwide frog trade. Damn.
I’m not by nature a pessimist. But this worries me because this is a major biological event that we don’t understand. When a single kind of animal dies in a worldwide pandemic that affects every continent where amphibians live, and we don’t have a model for why… that’s scary. It’s not hard to imagine something similar for the charismatic species we do care about: Humans, for instance.
Still, in science, not knowing is the normal state of affairs. In technology we worry about “unexpected side effects” otherwise known as the “unintended consequences” of technology.
In one famous case, the UN sent teams to dig wells in Bangladesh to improve the quality of water in small villages, thereby reducing infant mortality. This is a part of the world where 250,000 children would die each year from poor water quality. So they sank around 10 million wells and reduced rates of bacterial infection by 50%—a success! Except that the wells were relatively shallow and introduced large amounts of naturally occurring arsenic into the water supply, causing 20% of the population to suffer from heavy metal poisoning. Ultimately, around 10% of everyone who drank from those wells would die of lung, bladder, or skin cancers caused by the arsenic they were drinking.
In his book “Why Things Bite Back: Technology and the Revenge of Unintended Consequences” (1996) Tenner tells the story of why many of IBM’s tape drive systems suddenly started crashing in the mid 1970s. It turned out that after a large outbreak of Legionnaire’s disease (a bacteria that grows especially well in the warm, moist places in heating systems) many office buildings began injecting a bactericide into their HVAC systems. That was fine until the tiny tin particles from the active agent in the bactericide escaped from the ductwork and made their way onto tape drive heads in the computer rooms, causing a buildup that would cause misreads and failure. It was an unexpected interaction of a biological control affecting the universe of computing. The tape drives suffered from a cure for Legionnaires Disease.
In the book “1491: New Revelations of the America Before Columbus,” Charles Mann makes the argument that passenger pigeons, those birds we think of as prodigious in numbers, but then driven to extinction by American mechanized hunting methods, actually were relatively rare in pre-Columbian America.
How would you know this? By looking at the middens of native Americans that can be reliably dated to pre-1492. If you look for passenger pigeon bones, they’re pretty infrequent. Given that passenger pigeons numbered in the millions (and would strip a landscape of all edible nuts and grains as they passed, leaving behind a 2 inch deep swath of excrement), how could a culture that harvested every possible source of protein ignore these massive flocks? Answer: Because they weren’t there. What changed?
Mann argues that it was due a massive die-off in a keystone species that allowed the pigeons to grow to such numbers—the removal of a huge number of humans from the eastern seaboard caused a reduction in competition for their food supply. Pigeons and humans competed for the same nuts and seeds; removing a competitor over a broad range can cause “outbreak populations” that flood an ecosystem with hyper-growth of those species well-suited to take advantage. This was another unintended consequence of late 15th century European contact—diseases spread rapidly, killing much of the population. Some estimates are that as much as 95% of all American natives were felled by diseases introduced by early European visitors. The Americas of the 1500’s wasn’t virginal, it was a deeply, unwittingly disturbed ecology.
This view is supported by more recent work by Koch, Alexander, Chris Brierley, Mark M. Maslin, and Simon L. Lewis. "Earth system impacts of the European arrival and Great Dying in the Americas after 1492." Quaternary Science Reviews 207 (2019): 13-36. The key idea of this paper is that the European arrivals caused huge pandemics post-1492, which caused all of the previously forested and agricultural land to convert to an intensely forested state, causing a decline in global atmospheric CO2 concentration by 7–10 ppm in the late 1500s and early 1600s which globally lowered surface air temperatures by 0.15 C, leading to the “mini ice age,” which indirectly led to all of the wintery landscape paintings of the 16th century Dutch artists like Pieter Bruegel the Elder and Hendrick Avercamp.
Winter landscape with skaters near a castle (1608). Hendrick Avercamp.
(Part 1/2)