In 1983, Peter Morin published a paper in Ecological Monographs on the impact of salamander predation on larval anuran assemblages in experimental ponds. This paper formed one of the three chapters in Peter Morin’s PhD dissertation. Thirty-three years after its publication, I spoke to Peter Morin about the making of this paper and what we have learnt about this topic since then.
Questions sent by email no 26th July 2016; responses received by email on 1st August 2016
Hari Sridhar: This paper formed a part of your PhD dissertation under H.M. Wilbur. Please tell us what the motivation was for this specific piece of work, in relation to the rest of your PhD dissertation. Also, which came first: an interest in amphibians or an interest in understanding community structure?
Peter Morin: I had a long-standing interest in herpetology, going back to when I was a young boy of about 5 or 6 years of age. Early on, the fascination was with snakes and lizards, but amphibians were also interesting. My interest in natural history was encouraged by my father, and in college I learned that it would be possible to study herps. for a living, especially if I pursued a career as a college professor. At the time, the interesting work on herps. was being done in the areas of population and community ecology, so that steered me toward doing graduate work in community ecology. I applied to several graduate programs, got into all but one of them, and decided to study at Duke with Henry Wilbur, who was a rising star in the field. Henry mostly worked with amphibians then, so that led me to work on amphibians too. Along the way, I came to appreciate some of the major issues and questions in community ecology.
The work in the Ecological Monographs paper was one of the three chapters in my dissertation. All three chapters were based mostly on results from a single community-level experiment conducted in 1980. The chapters focused on the responses of different taxonomic groups, frogs, salamanders, and zooplankton, to the same experimental manipulations of top predators – two species of salamanders.
HS: You say your experiments “were inspired by the natural history of temporary ponds in the Sandhills Game Management Area”. Can you tell us a little more about your connection to this area and how it influenced you?
PM: Henry Wilbur’s research at the time was focused on amphibians in the Sandhills, so much of my early field experience in graduate school involved visiting ponds with Henry and his other students, sampling the ponds to see what lived there, and learning about what was common and rare. One thing was obvious: newts were abundant and nearly ubiquitous. They were the top predator, or one of the top predators, in most ponds. That made them a logical thing to study. There was also a high diversity of frogs breeding in the ponds, which made the question of what allowed so many ecologically similar species able to coexist an interesting one.
HS: Who came up with the idea of using cattle-watering tanks for the experimental setup?
PM: Henry Wilbur had already had a grant funded to use cattle-watering tanks as replicated ponds in the Sandhills. The idea was to place tanks in natural areas, controlling for size, historical effects, and the surrounding habitat, to create comparable communities that could be sampled in comparable ways. Even then, most of the tank communities tended to be rather unique, probably depending on the history of colonization, so it seemed like exerting more experimental control over starting conditions would be useful. I asked Henry to buy me some tanks that I could use for controlled experiments on the impacts of predators on frog tadpole assemblages. The rest is history.
We weren’t the first people to use analogous containers as experimental units. Stuart Hurlbert had done this with small pools in the early 1970’s, and Hall, Cooper and Werner had done things on a larger scale in artificial ponds, first at Cornell and then later at Michigan State.
HS: Would you know what has happened to this experimental setup after your time at Duke? Are these tanks still being used?
PM: The ‘tank farm’ grew in size while I was at Duke, and afterwards, until Henry Wilbur moved to the University of Virginia. I don’t know what became of the original tanks. They were a bother to maintain, with most requiring a new coat of epoxy paint every year with much attendant scraping off of old paint. Most people using similar things for their experiments, including me, have switched over to plastic tanks which are easier to maintain.
HS: If you don’t mind my asking: how come your PhD supervisor H.M. Wilbur was not an author on this paper?
PM: Henry had an enlightened and generous philosophy about authorship. This probably came from his own experience at the University of Michigan. Basically, if he wasn’t involved in the set-up, data collection, analysis, and writing, he didn’t see the point in being a coauthor. I have applied the same rationale to my own students, though you don’t see that happening very much anymore. It wasn’t unusual in 1983 to see mostly single-authored papers in Ecological Monographs or Ecology. Now it’s rare.
HS: Can you give us a sense of what a typical day was like for you when you were doing these experiments?
PM: Once the tanks were set up, animals collected and introduced, and things were running, the daily routine was to visit the tanks, collect all metamorphosing amphibians from each tank, return those to the lab, where they were identified to species, weighed, and measured. That happened from sometime in April through the end of summer. There were weekly zooplankton samples taken from each tank. Once a week I went out at night to try and capture the salamanders so that I could monitor their growth and survival. Each was uniquely identifiable by its color pattern. Depending on what was metamorphosing and when, this could keep you rather busy. And then, the metamorphs were released periodically back in the Sandhills.
HS: You acknowledge a number of people for help in “collecting frogs or maintaining the experiments”. Were all of these people also students in Duke University?
PM: Mostly, but my wife, Marsha Morin, who is not a biologist by training, was also a big help in collecting the frogs that went into that experiment. She probably caught more frogs than anyone else!
HS: How long did the writing of this paper take? Did you have a particular writing routine – where you wrote, when you wrote – at that time?
PM: It’s hard to recall the exact time frame, because this was just one chapter in my dissertation, and I was basically working on all three at the same time, along with a couple of other projects. Most of the writing happened in my office at Duke. I was one of the first students in my department to write my dissertation using a personal computer/word processor, a Commodore 64. Computers and word processing have changed since then, mostly for the better
HS: How were the figures for this paper made? Were they drawn by hand?
PM: Some of the graphics were roughed out on a graphics terminal, but a lot of the artwork was done by hand, by me, either using press type or other ancient technologies, like a pen and India ink. That is probably why one of the species names is spelled incorrectly. Things have gotten much better since then, except for my spelling.
HS: Did this paper have a smooth ride through peer-review? Was Ecological Monographs the first place you submitted this paper? How different was the final published version from the first submitted draft?
PM: Relatively. Ecological Monographs was the first place that it was submitted to. A preceding paper, based only on the first three species to complete metamorphosis, had appeared in Science. The major difference between the submission and the final paper was inclusion of an appendix spelling out the details and rationale behind the multivariate analysis of the results.
HS: You thank Douglas E. Gill for “many helpful editorial suggestions”. Was Dr. Gill the handling editor of your paper at Ecological Monographs?
PM: Doug was the handling editor. He is an excellent ecologist, and he was an authority on newts. His comments and those of the reviewers made it a much better paper.
HS: You say “Computing funds were provided by the Department of Zoology, Duke University”. Can you tell us a little more about what “Computing funds” were?
PM: Where to begin? When I began graduate school, personal computers did not yet exist, or if they did, they were mostly used by hobbyists. Real computing power, which is now dwarfed by the laptop computer on which I am writing this, resided in massive room-filling machines that were time-shared by universities like Duke, UNC Chapel Hill, and NC State. The costs of running and maintaining those facilities were shared, and subvented to some extent, by charging users for the computer time used. I think this was mostly ‘funny money’, but major users were expected to pay for their computer use with grant funds. I was a minor user. One communicated with the computers using decks of IBM punch cards, read through a card reader, and results were returned some time later by a device called a line printer. It is now all delightfully archaic. About the time I finished my degree, it became possible to communicate directly with the time-shared machines using new things called video terminals. I thought I’d died and gone to heaven…
The changes in computing power that I’ve seen since 1976 when I started graduate school, and the ease of use of computing technology for statistical analysis, graphics, modeling, and things we never dreamed we’d be using computers for are unfathomable for today’s typical undergraduate student.
HS: What impact did this paper have on your career? In what way did it influence the future course of your research?
PM: I guess that receiving the Mercer Award from the ESA for this paper probably didn’t hurt my career. The impact of any single paper is hard for me to judge. These days, more students recognize me for my Community Ecology book than for any of my papers. I continued to work on amphibians for quite a few years afterwards, as did some of my students, but then turned to other systems to address different questions. However, right now, one of my students is working on amphibians again, with a focus on the microbial ecology of amphibian disease resistance.
HS: What was the reaction to this paper at the time it was published?
PM: I remember getting a large number of reprint request cards in the mail. You don’t see those any more, either. Oh yes, in the days before pdfs, we sent out things called reprints to people who requested them.
HS: It’s now 33 years since this paper was published. Would you say that the main conclusions of this paper still hold true?
PM: Pretty much. One take home point was that predators have a big effect of community structure, favoring species that may not be the best competitors, but that are able to coexist with predators via various strategies and adaptations. Predators remain common, and the spring peeper remains one of the most common frogs in eastern North America, I think because it deals well with predators despite being a pretty poor competitor.
When I was planning my dissertation work, ideas promoted by Bob Paine and Joe Connell were still taking hold, such that the role of predators in driving community patterns were still somewhat controversial. That is all much clearer now.
We didn’t know much about other natural enemies back then, specifically the ones that are now having huge impacts on some amphibian populations – pathogens like Bd. That could change everything.
HS: If you were to redo this experiment today, would you do anything differently, given the advances in technology, ecological theory and analytical tools?
PM: It would have been nice to have a predictive mathematical model of the community dynamics to compare with the empirical results. People have also become hypercritical about the use of artificial communities, so it would be nice to able to do the experiment, or part of it, in natural ponds. That, however, isn’t so easy.
HS: You say “early-breeding species may have a lingering impact on resource availability, subsequently influencing the growth of species exploiting a pond later in the same year (Seale 1980). Such priority effects are an interesting topic for future research”. Did you research “priority effects” further, after this paper? In general, did “priority effects” become an important area of research in the period after this paper was published?
PM: We have studied priority effects in a variety of systems including amphibians, odonates, and microbes. I followed up on that, as did many, many others.
HS: You say “the potential importance of newts as keystone predators is unambiguous”. Was this statement borne out by subsequent research?
PM: It appears to work in other artificial pond experiments, and it also shows up in surveys of natural ponds done by Bill Resetarits and his colleagues. Some people don’t see much evidence for it, especially in systems where amphibian densities are low and rarely get to the level where competition is important. The question there is whether low densities are set by predators, in which case there is no inconsistency, or whether low densities are set by supply-side dynamics, which raises other issues about what controls inputs in metacommunities.
HS: Were your experimentally-derived patterns subsequently shown to be consistent with patterns in natural pond communities?
PM: Somewhat, but I would like to see a much larger data set address the patterns in nature. Unfortunately, it’s not the kind of confirmatory study that any funding agency is likely to support. And it would be nice to see what happens before an amphibian plague wipes out the natural populations.
HS: At the time this was published, did you anticipate that it would be cited so much? Do you know what this paper has been mostly cited for?
PM: I hoped that it would be cited, and it’s nice to see that it has had some staying power over the years. According to Google Scholar, it is not my most highly cited publication, but it’s in the top 10.
HS: What would you say to a student about to read this paper today? What should he or she take away from it? Would you add any caveats?
PM: I guess I would say ‘Sorry that it is so long.’ I hope they would get a good idea of what a publishable chapter in a dissertation might look like.”
HS: Have you ever read the paper after it was published? When you read it now, what strikes you the most about it?
PM: Oh yes, I have read it. It’s still very long!
HS: Is this your favourite paper among all the papers you have published? If yes, why? If no, and if you do have another favourite, which is it and why?
PM: Although this is one of my early papers, I still like it. However, I’m basically against the idea of picking favorites. It’s a bit like having kids (which I don’t have), or graduate students (which I do). They are all special, in different ways.