Demonstrating extinction: the amphibian update

Those of you who follow Zoo Atlanta know that, for the last 15 years or so, we’ve been heavily involved in both the basic research and the conservation aspects of the tragedy of global amphibian declines and extinctions. As much as we like to celebrate major research advances, discoveries and publications, a big paper this week is a tough one to celebrate.

My colleagues and I have been studying and tracking the scourge of the pathogenic amphibian chytrid fungus, Batrachcohytrium dendrobatidis (Bd, for short) for decades. Being able only to study it, and not stop or mitigate its devastating consequences, has been a central conundrum in careers of my entire academic cohort. One of the absolutely most frustrating problems for all of us has been the nagging question of “Just how many amphibians have we lost?” Extinction, as it turns out, is a very difficult phenomenon to demonstrate conclusively. The concept of “zero animals of a species remaining” is simple, but the evidence is never stronger than “well … don’t know … we can’t find them,” and occasionally a missing species reappears in small numbers. So, this numbers game is difficult, and it has been especially difficult with amphibians globally because the research community simply did not have the baseline data on the abundance of virtually any of these species before they started to disappear. The fact is, our ability to really estimate the severity of amphibian declines has been severely hampered by lack of data, or by poor data. This has bothered all of us herpetologists in the trenches for a long time.

Enter Ben Scheele, from the Australian National University, in Canberra, Australia! Ben was fearless enough to wrangle 40 co-authors from all over the world to work through a very careful system of data-capture that he developed. The goal was to simply accept that we will never have the data necessary to properly assess amphibian losses, so we proceeded to do the best we could with admittedly spotty data. To be honest, when Scheele contacted me (to provide summaries of my many years in the field in Mexico and Guatemala), I was hesitant. I deferred for a while, and finally I started to see the brilliance in his system. Aside from missing data, I could only see that his system would produce very conservative results – underestimates of declines and extinctions. But I had a change of heart. Ben’s approach was so methodical that I realized it would allow us to produce solid, evidence-based estimates of losses and, given such a solid mathematical foundation, it would allow me to legitimately declare these numbers to be conservative underestimates.

When the final numbers started to emerge from Ben’s mental factory, they were shocking enough that even I stopped worrying about conservative underestimates. The goal was to assess the numbers of species directly affected by the pandemic of Bd that had its height in the 1980s. The results, published this week in the journal Science, are shocking: 501 amphibian species severely affected by Bd, 90 of which appear to be extinct. These results allowed our team to make the terrifying concluding statement that Bd is the most destructive pathogen that biodiversity has ever known.

So, the big summary paper is out, and I am left with one of the oddest feelings of my research career. We finally have some defensible numbers to highlight what many of us have done with the bulk of our careers, but the feel-good wrap that usually comes with mega-retrospective analyses like this is simply not there. I never, ever thought that as a scientist, I would roll out my best work and wish it was all wrong.
Joe Mendelson, PhD
Director of Research

Full paper citation:
Scheele, B. C., F. Pasmans, L. Berger, L. F. Skerratt, A. Martel, W. Beukema, A. A. Acevedo, P. A. Burrowes, T. Carvalho, A.                    Catenazzi, I. De La Riva, M. C. Fisher, S. V. Flechas, C. N. Foster, P. Frías-Álvarez, T. W. J. Garner, B. Gratwicke, J. M.                Guayasamin, M. Hirschfeld, J. E. Kolby, T. A. Kosch, E. La Marca, D. B. Lindenmeyer, K. R. Lips, R. Maneyro, C. A.                    McDonald, J. R. Mendelson III, P. Palacios-Rodriguez, G. Parra-Olea, C. L. Richards-Zawacki, M. O. Rödel, S. M.                        Rovito, C. Soto-Azat, L. F. Toledo, J. Voyles, C. Weldon, S. M. Whitfield, M. Wilkinson, K. R. Zamudio, and S. Canessa.              2019. The aftermath of amphibian fungal panzootic reveals unprecedented loss of biodiversity. Science 363: 1459–1463              + Suppl. Mat.
                             (Perspectives: Greenberg, D.A., and W.J. Plan 2019. A deadly amphibian disease goes global. Science 363:                                     1886–1388. DOI: 10.1126/science.aax0002)

Organizations like Zoo Atlanta work to preserve future options for wildlife. One such example is the Panamanian golden frog, which is now considered extinct in the wild as a result of habitat loss and the spread of the chytrid fungus. Institutions in Panama and AZA zoos, including Zoo Atlanta, maintain assurance colonies of this species in hopes of one day repopulating the frogs in the wild when current threats are eliminated. Learn more here.