Revisiting Terborgh et al. 2001

In 2001, John Terborgh, Lawrence Lopez, Percy Nuňez, Madhu Rao, Ghazala Shahabuddin, Gabriela Orihuela, Mailen Riveros, Rafael Ascanio, Greg Adler, Thomas Lambert and Luis Balbas published a paper in Science demonstrating a trophic cascade on predator-free islands, which were created as a result of the construction of a dam. Fifteen years after the paper was published, I spoke to John Terborgh about the making of this paper and what’s happened on these Venezuelan islands since.

Citation: Terborgh, J., Lopez, L., Nunez, P., Rao, M., Shahabuddin, G., Orihuela, G., Riveros, M., Ascanio, R., Adler, G.H., Lambert, T.D. and Balbas, L., 2001. Ecological meltdown in predator-free forest fragments. Science 294(5548): 1923-1926.

Questions sent by email on 12th August 2016; responses received by email on 28th August 2016.

 

Hari Sridhar: I would like to start by talking a little bit about your motivation for doing this study. In 1988, you published a short essay titled “The Big Things that Run The World-A Sequel to E. O. Wilson“, in which you lay out the possible consequences of the loss of top predators on lower trophic levels. In that it almost seems as if you anticipated your subsequent findings in Lago Guri. When and how did you first learn about Lago Guri, and why did you decide to work there?

John Terborgh: I learned about Guri from a colleague, Warren Kinsey, a primatologist, who told me about his new research site in a giant hydroelectric project in Venezuela.  I hadn’t known about Guri before that. It was 1990. Later that year, I went with two graduate students and Warren to visit his camp on one of the larger islands. It was exactly what I had been looking for, for many years – a giant replicated fragmentation experiment.

Yes, the “Big Things” commentary did anticipate some of the findings, but I had received a lot of criticism and disbelief from colleagues about the Big Things article and was anxious to find support for my interpretation in a replicated system that would not be subject to the N = 1 criticism.

 

HS:  This paper has 11 authors. How did this group come together and what did the different authors bring to this study? Did all members of the group ever come together in one place at any time?

JT: I first saw Guri in 1990 but we didn’t begin the research in earnest until 1993. The Science article was published, I believe, in 2001. By then, the project had attracted a number of PhD and Master’s students, each of whom undertook a sub-project. The Science article published a summary of results to which the 11 people had contributed. Were we ever all together in the same place? I couldn’t say, but most of us were in the field together for one or more years.

 

HS: How long did the writing of this paper take place? At the time of writing this paper, did you have a particular writing routine, with regard to where and when you wrote?

JT: Do you mean the physical act of writing? That didn’t take long. I write quickly. It might have taken me a day or two. What took much longer was compiling and analysing the data. I do most of my writing at Cocha Cashu in Peru (where I am now), but I don’t remember where I wrote the Science article.

 

HS: Did this paper have a smooth-ride through peer review? Was Science the first place you submitted this paper to?

JT: Yes, I was fortunate and it was quickly accepted.

 

HS: How was this paper received on publication? Did it attract a lot of attention in academia and the popular press?

JT: By now it has attracted nearly 1000 citations, so that suggests it did attract attention. As for the popular press, I can’t say.

 

HS: Did this paper, in any way, influence your future research trajectory?

JT: I would say that trajectory was already quite well established.

 

HS: Today, 15 years after its publication, would you say that its main conclusions still hold true, more-or-less?

JT: Definitely, as further detailed in the “Trophic Cascades” book I published with Jim Estes and others more recently.

 

HS: If you were to redo this study today, would you do anything differently, given the advances in technology, theory and analytical techniques?

JT: There was something I wanted to do, but didn’t do, that would have been a clincher. That was whole island experiments, in which we removed leaf-cutter ants from some, rodents from some, and both ants and rodents from others. And, of course, there would have been untreated controls. We were starting to implement these experiments at the end of the study, but then two things happened, both beyond our control. First, there was a 3-year drought that brought the water level in Lago Guri down 26 meters. Yes, that’s 26 meters. This exposed many km2 of lake bed and effectively connected all the experimental islands to each other and the mainland. The last year we were there – 2003 – we found 6 different predator species on islands where we had not previously seen any predators at all, over a 13-year time span. This was convincing evidence that, in fact, the islands were predator-free during the main period of our research. Second, Hugo Chavez came in as President of Venezuela in 1999 and was cracking down on foreigners, especially Americans. There was no way we could have continued the project under his government.

 

HS: In the paper you say “We expect that processes set in motion at the time of isolation will run their course on most small islands in another few decades. Hyperabundant folivores threaten to reduce species-rich forests to an odd collection of herbivore-resistant plants. Along the way, much plant and animal diversity will be lost. The end-point is likely to be a biologically impoverished system”.  Would you say these islands are on this trajectory you described 15 years ago?

JT: I think it is likely, and I wrote as much in a later publication in which I showed that the plant community on top of leaf-cutter ant colonies consisted of many plant species that were rare in the flora but apparently resistant to ant foraging.

 

slide33

A slide showing the impact of herbivores on the vegetation of a predator-free island ( © John Terborgh)

HS:  Do you continue to work in these islands? When was the last time you visited them?

JT: As I said above, in 2003. But by then, the ‘experiment’ had been broken by the drought. I don’t think scientists will be going back to Lago Guri until after the current Chavista government has fallen and been replaced with a more outward looking one.

 

HS: In the 15 years since this paper was published, have you ever read the paper again? When you read it now, what strikes you the most about it?

JT: Maybe I read it once. I tend not to dwell on the past.

 

HS: This paper has been cited over 1000 times. At the time of its publication did you anticipate that it would have such a big impact? What does it mainly get cited for?

JT: This is the way the world works. Nothing in that paper is unique to the paper itself. All our results have been published in much greater detail in other publications, of which I now count over 45. Yet, it is the Science article that gets all the citations. My hunch is that a lot of the attention that paper has attracted comes from one word, “meltdown.” Nobody can pass up that word. Had I submitted it with a different, more prosaic title, it might never have been published.

 

HS:  Among all the papers you have written, is this one of your favourites? If yes, why?

JT: I would say, no, because, as I mentioned above, it was merely a summary of a lot of work done by a lot of people. I was only the messenger who wrote it. The paper from Guri that I consider our crowning accomplishment was not published until later: Terborgh, J., P. Nuñez V., B. Balukjian and M. Silman. 2006. Vegetation dynamics of predator-free land-bridge islands. Journal of Ecology 94: 253-263. This contained the real meat of the project, the indirect effect of predator loss on the plant community. And the effects were drastic – nearly all plant species in decline under the onslaught of leaf-cutter ants and other generalist herbivores. Yet, we had great difficulty publishing the results. It was rejected by two journals before it was finally accepted. But that was more than 2 years after it had been first submitted.

 

HS:  What would you say to a student who is about to read this paper today? What should he or she take away from this study published 15 years ago?

JT: I would tell him/her to read a more recent Science paper I wrote with Jim Estes and others: Estes, J. A., et al. 2011. Trophic downgrading of planet earth. Science 333: 301-306. This is more up-to-date and carries a stronger message about the harm that humans are doing to nature, and the irrevocable changes that humans are causing in ecosystems all over the world

 

 

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