The Last Golden Toad

Prior to the series of amphibian lectures by our visiting professor, Dr. Mark Wainwright, I did not know the full extent of the amphibian crash of recent years, and I did not know anything about the subsequent partial recovery. At a research talk last summer, I had heard about the golden toad—possibly one of the most famous tropical amphibians—and the story of its decline: field biologists found fewer and fewer toads each year until the last one disappeared; none have been seen or heard since. The professor giving the talk said that the loneliest thing he could imagine was being that last remaining golden toad.

This week at Monteverde, I learned that the golden toad was one of many amphibian species around the world that seemed to disappear within a period of a few years. But many years later, about half of these species started increasing in abundance again. During our lecture, Mark led us through various possible causes of the crash, discussing the validity of each hypothesis. There were many hypotheses to choose from, but it was difficult to explain how the amphibian crash could have occurred in such a narrow time period (meaning that continuous or recurring processes such as global warming or El Niño were unsatisfying explanations) and in such a wide spatial distribution (meaning that specific land use policies were unlikely to be responsible). We agreed that the strongest explanation was an epidemic: capable of appearing and devastating populations very quickly, and spreading between populations on a large spatial scale. Mark told us about a chytrid fungus that had been found on many frogs around the time of the population crash, which is generally thought to be the most likely explanation.

Discussing each of the hypotheses for the frogs’ disappearance was interesting, but for me, the more intriguing part of the talk was about recovery. One tourist took a picture of a frog next to the trail and asked her guide to identify it; it turned out to be a species that no one had seen in 30 years. Many of the “missing” species became very common as they repopulated, and we found some of them on our night walk. Most likely, the remaining populations of frogs subsequently recovered and expanded because the extinctions of other species had opened up niches. I found it striking that these species were present, though presumably in low numbers, without being seen or heard by anyone for years. How had all of the sampling efforts of worried field biologists missed all of these frogs? Were they in hiding?

What this means to me is that when I am in the field, I likely only observe a small percentage of the species or interactions that occur. That’s one of the things I find most fascinating about the biological sciences: there is so much about biology that we do not yet know, as with any other field, but there is likely quite a bit that we don’t know that we don’t know. It is thought that around 80% of species currently in existence have not been discovered, and the proportion of undiscovered fossil species is certainly even larger. It’s a little dizzying to imagine entering the field of biological research with little idea of what the search space of unanswered questions looks like.

But developments in technology are certain to help, bit by bit. This week, I’ve been reading “Frankenstein’s Cat”, a book about recent advances in biotechnology. One of the chapters discusses animal tracking chips for monitoring endangered populations. I’m not sure whether this is also being done, but fitting tiny non-invasive cameras on animals would be a cool way to learn about areas that are difficult to reach or animals that are shy around humans. And of course, increasing our ability to understand natural environments in this way would be helpful for tackling conservation issues such as the recent amphibian crash and recovery.

Reena Debray

Duke University