In a paper published in Ecology in 1969, Daniel Simberloff and E.O. Wilson reported the findings of a “defaunation experiment” they conducted on mangrove islands in the Florida Keys, to test the Theory of Island Biogeography proposed by Robert MacArthur and E.O. Wilson. In addition to this paper, Simberloff and Wilson published two other papers on this experiment, one describing the methods and the other presenting a model based on the data. These three papers together formed the bulk of Simberloff’s PhD dissertation under Wilson. Forty-seven years after the paper was published, and nearly 50 years after the experiment was conducted, I spoke to Dan Simberloff about his motivation to do this experiment, memories of field work, and the status of these mangrove islands today.
Citation: Simberloff, D. S., & Wilson, E. O. (1969). Experimental zoogeography of islands: the colonization of empty islands. Ecology, 50(2), 278-296.
Date of interview: 23rd August 2016 (on Skype)
Hari Sridhar: I want to start by asking you about your motivation to do the work presented in this paper. This work came during your PhD with E.O. Wilson. Did you join E.O. Wilson’s group already knowing that this is what you wanted to do, or did the idea for this study come after you joined?
Dan Simberloff: Well, when I joined Ed’s lab, I had already read a number of papers on biogeography, and I had begun to read a number of other papers in ecology, especially about community-level ecology. But remember, I had been a math major as an undergraduate, and so when I joined Ed’s lab, we made a deal. He said he would teach me all the biology that I needed to catch up on, and, in turn, I would help him develop his mathematical understanding, which he had very little of in college and graduate school. I didn’t have that particular project in mind when I joined. I had read the 1963 paper by MacArthur and Wilson, and soon after I joined his lab Ed handed me a rough draft of what ultimately became the 1967 book ‘The Theory of Island Biogeography’ and asked me to comment on it. I read it, made a number of comments and also said: “You know, the theory seems sound, but it has not really been tested in any direct way.” And Ed said: “Well, why don’t you test it?”
I thought about that, and I had already visited small islands in the Gulf of Maine, north of Boston, where I had looked at beetles, ground beetles. I had recognised that each island had a different number of species and a somewhat different set of species, and I thought it might be possible to remove them to test the theory. But I quickly realised, that winter, that I wouldn’t be able census them for half the year. The seas were too rough and the weather was unbelievable. The islands were often covered with snow. Ed, who had visited the Florida Keys said: “What about these little mangrove islands in the Florida Keys?” I went down there and looked, then he came down and looked with me, and we decided that they were about the right size. That’s how that whole project came about, and that became my doctoral dissertation.
HS: This paper is full of really detailed natural history descriptions. Was this something you picked up after you joined Ed Wilson’s lab?
DS: No, I will tell you how that came about. I had certainly collected insects before, even since childhood, but I didn’t have formal training. I was taking entomology courses with Frank Carpenter at the time. But what we did was, for most of the major groups – Ed, of course, knew all about the ants – but for other groups, like spiders and orthopterans etc, it turns out Ed knew specialists in each of these areas, because he had earlier helped them in their projects, by identifying ants for them. They were all part of this community of experts in different invertebrate groups, and a large part of that was expertise in natural history. Ed arranged for me to contact them, and some of them even came down to the Florida Keys to give me a crash course in learning the natural history of these species, and, in particular, how that would help me to find them, and to understand why they were present or absent on these islands. I learnt it on the run, as you might say.
HS: Yes, I notice, in the Acknowledgments, a long list of people who helped you in identifying the animals.
DS: Yes, and they did much more than that. Some of them simply identified things, but many of them provided information on the natural history, and some of them provided very extensive information that helped us to understand what was going on.
HS: I also wanted to ask you specifically about some of the people you mention in the Acknowledgements. You thank a person by the name of Robert E. Silbergleid.
DS: Yes, Bob Silbergleid was a huge help. Early on, it became apparent that I could use an assistant. It was important, both for safety (so as not to be working alone in isolated waters), and the sheer amount of work I was trying to do. Also, I wanted to assemble a ‘species pool’, by looking at what was there on the surrounding mangrove areas on much larger islands. We started to look for really good undergraduate students, who were willing to spend a lot of time in field on the project. Bill Brown, who was another of Ed’s long-time colleagues, another myrmecologist and an expert evolutionary ecologist, suggested Bob Silberglied. He said: this is the person you need. Ed met Bob and then sent him to me. That’s how we ended up recruiting Bob, and he was a huge help. He did a fantastic amount of work. I don’t know if you know more about him, but he went on to become Ed’s graduate student, got a doctorate, and was a productive insect systematist and evolutionist. Unfortunately, he died young in a tragic plane crash – the Air Florida crash in 1982 right in the heart of Washington D.C. The plane went right into the Potomac River and a number of people died, and Bob Silbergleid was one of those.
HS: I’m sorry to hear that.
HS: You also thank Joseph Beatty and Edward Mockford for identification of specimens and advice on experimental technique.
DS: Joe Beatty was an arachnologist, a very fine one, and he knew everything about spiders. He had been at Harvard previously and then got a job at Southern Illinois University. He was an enormous help in showing me how to find spiders and helped me identify spiders. I learnt a lot of natural history about different groups of spiders from Joe. Ed Mockford was a psocopteran expert. I realised, really early on, that psocopterans were going to be major colonists in my dataset. There were a number of species and some of them showed up early in the colonisation. There aren’t many specialists in psocopterans then, and Ed Mockford was one whom Ed Wilson knew. I guess they had interacted in some problem before, and Ed put me in touch with him. He identified all of our psocopterans, gave me lots of information about their natural history of psocopterans, and continued, throughout the project, to comment on the psocopterans I identified and provide information on the biology of the psocopterans I found.
HS: You also thank S. Peck, H. Nelson and R.B. Root for help in island censuses. Were they fellow graduate students?
DS: Not all. Nelson and Peck were, but not Root. Dick Root was a very prominent ecologist at the time. He was already a full professor then. Dick was very interested in community ecology and pretty much developed the idea of the ecological guild. He died a few years ago of Alzheimer’s disease. Nelson was a graduate student who helped me sometimes. Stuart Peck was also a fellow graduate student, who knew a lot about insects, especially about beetles.
HS: Then you thank John Ogden for helping you culture many arthropod colonists.
DS: Yes, John Ogden was an assistant biologist for the Everglades National Park. He was a young man, already had his degree and was the assistant to Bill Robertson, who was the park biologist. Subsequently, John Ogden became the park biologist. John too died a few years ago. But anyway, I had to, often, rear animals through to the adult stage to identify, because I would find larval stages or even eggs. John helped me with that. He provided a place where I could do it and kept an eye on them.
HS: Could you give us a sense of fieldwork during this one year, from the time of defaunation and through the time when you were doing all the monitoring? Did you do all the work mostly on your own? Where did you stay? Did you set up a field laboratory etc.?
DS: No, I did not have a laboratory set up there. I stayed there much of the time, but I would periodically go back to Harvard, to deal with all the data, to deal with identifications, and in one case course work, and then I would fly back again. I had rented a house, and the house was my laboratory. Every morning when I was down there, when the weather wasn’t too bad, I would go to a particular marina depending on which island I was planning to work on, go to the island for the whole day and come back. I learnt a lot about using small motors navigating them. That’s what I did. It was very intensive fieldwork.
DS: Yes, there is no doubt. It was hard work! But at the same time, it was exciting and interesting. We had this interesting experimental technique; no one had done anything like this before. I was learning a huge amount that no one had known before. I was watching the colonisation of these islands, and almost every day found something new and interesting. It was grueling, very grueling, sometimes physically unpleasant. Especially the sharks and mosquitoes! But it was so exciting and important, and I was glad to do it.
HS: Were there alligators where you worked?
DS: No, not on the mangrove islands. But in the extreme south of the Florida Keys, including one place where I worked and lived called Big Pine Key, there is a small population of crocodiles, which are much more dangerous than alligators. I encountered them twice when swimming in canals at the end of the day. But they don’t go to the mangrove islands. But sharks are constantly around there. To sample some of these islands, I had to anchor some distance away and wade to the island. I had to always keep an eye out for sharks, and sometimes hit them on the top of the head with an oar that I carried with me. Mosquitoes were sort of a constant issue, in the summer and late spring and early fall. But you know, they were only mosquitoes, so I learnt to live with them.
HS: Were you on your own most of the time?
DS: I was either on my own or I would have one helper. Sometimes Bob Silbergleid would help me and sometimes someone else would visit. I was more often than not on my own. I would usually drop Bob Silbergleid off on the larger islands or the nearby mainland where he would be collecting insects to assemble the species pool that we were working with. Occasionally, Bob or someone else would accompany me during my sampling on the islands. But usually I was alone.
HS: Did Ed Wilson visit you during your fieldwork?
DS: Once in awhile during sampling, but certainly many more times beforehand. But we were in constant touch. We didn’t have email in those times but I would send him information by mail, and I would go back periodically. So, we spent a huge amount of time together.
HS: Did you have a telephone in your field station?
DS: Yes, I had a telephone in the house that I rented.
HS: In the paper you mention one particular day – 26th February 1967 – which was special because it was the day when the temperature was the lowest in a long period. The temperature went down to 9.5o C. Do you remember anything more about that day? Did you sample on that day?
DS: It was a day I sampled. In the morning it was pretty cool, but it then warmed up. I certainly remember it being cold in the morning and then everything was normal. No, I don’t remember anything else significant from that day.
HS: Do you remember how long you took to write this paper, and when and where you did most of the writing?
DS: Sure. I wrote all three papers related to this project and Ed edited them. I did them all at Harvard, once I was back. It was a large complicated experiment and then there was the model too, so there was a lot to write. But it was pretty straightforward for me to write it. I knew what I wanted to say, I don’t have trouble writing and Ed was right there. I’d write something, give it to Ed, and he would return it with comments quite quickly. I also had a big Introduction to my thesis itself, which is not in these three papers. That chapter was about the history of these islands, analogous situations where natural forces have removed species from islands, biogeography of islands etc. I was simultaneously writing my thesis and these three papers. It is not trivial to write three papers, but it was not a crushing burden either. It was what I expected and we did it.
HS: Right from the beginning, was the plan to write three papers from this project?
DS: Not right from the beginning. But once we had done the work and discussed how to shape it, it became clear pretty quickly that this would be a good way to separate the parts into distinct units and assign authorship.
HS: Was Ecology the first place you submitted this paper to?
HS: Do you remember if this paper had a relatively smooth ride through peer-review?
DS: Boy, that’s an interesting question! No one has ever asked me that. Thinking back, I certainly remember comments, but I don’t remember anything that was very difficult to deal with. I can say, with assurance, that the peer-review was not problematic. The comments were basically constructive, they were not a huge number, and we dealt with them.
HS: What about the 1970 paper, where you present the results of two years of monitoring. How did that come about?
DS: That wasn’t planned at the outset. But we realised it would be useful to do, and luckily I was able to find the time to go there and do it. It wasn’t part of the original plan. Now, I’m actually trying to figure out a schedule to go down there for a month, with some help, and do a 50-year census. I think it will be interesting and historical. I’m in good physical shape, so I’m going to try to do it, somehow.
HS: Wow. That will be something. Did you continue working on these islands after your PhD?
DS: Yes. I did two other big experiments there. In one of them, I censused a bunch of islands, and then reduced the size of all but one, which was the control, by hiring a crew to cut down the mangroves. I waited and then censused again, and then I did it a second time on a subset of those. That was a big paper in Ecology, in 1976 I think. I also did an experiment where I turned islands into archipelagos by cutting canals between parts of them, so that what had been one big island became a group of small islands. Then I censused them to see how they had changed. I published that with my colleague Larry Abele in Science. I don’t remember the exact year. That became pretty controversial. Not the work itself, which was what it was – we had real data. But the implications of it for conservation were seen to be enormous and people didn’t like it. So it led to controversy.
HS: When was the last time you visited this site?
DS: I wasn’t right at that site, but roughly 10-12 years ago, a British film company did a big documentary on Ed Wilson, and a major portion was about the work in the Keys. They flew us – Ed and me – down to the Keys and we went out in a boat near the area around Islamorada, near two of our islands. They photographed me climbing the mangrove trees and looking at insects and what have you. But I have not looked at the islands that I censused systematically since the end of that two-year census that was published in 1970. That’s why I’m really interested in doing the 50-year recensus.
HS: Would you know if these areas have changed a lot since the time of your study? Are these islands protected?
DS: Yes, they are protected. Two of them are within the bounds of Everglades National Park, and four of them are part of the National Wildlife Refuge. Now they can be damaged anyway and I haven’t seen them so I don’t know. One of them is in an area where it has been damaged, when they built a big expressway. But six of the seven are still there. I believe they are still there, and the general area hasn’t changed.
HS: Is there a lot of tourism in this area?
DS: Oh yes, of course, but no one goes to these little mangrove islands. They are viewed as hellholes, because of the mosquitoes, and they are sometimes hard to get to. And, you know, they are just trees growing out of the water. People don’t go to them. On the Florida Keys, along the overseas highway, which goes all the way down to the Key West, there is a lot of development there. But these are several miles off into Florida Bay, and they are isolated.
HS: Did this paper attract a lot of attention when it was published?
DS: Yes, a huge amount. It was written about in several places. It was even in newspapers when we gave a talk about it at the AAAS meeting, and it became widely cited quite early. People recognised it as interesting.
HS: At the time you were doing this work did you anticipate at all that it would have such a huge impact over the years? People still talk about it as one of the most important experiments in ecology.
DS: No. I thought it was a really great project. I liked the idea of testing the theory. That was my idea that we needed a test. I could see that this system that Ed suggested was a good one to do the test in. But remember, I was a beginning grad student at the beginning of this. I was coming from Math, and so I didn’t know much about ecology academia, and publishing, and about exactly how this would be received. So, I wasn’t really expecting it to be a classic, which it did become.
HS: Do you know what it mostly gets cited for?
DS: Yes, I do. It is cited for several things. It is cited often as a big experiment in ecology, or experiment at the community level. That kind of thing. It’s been cited a number of times by people looking to use the data to show larger patterns, e.g. the trophic structure of the food web, or which species colonised when, or species that are able to coexist or not coexist. So, big issues of composition and community structure. And there have been several prominent efforts along those lines. What else? Then finally it is cited for – even though it is pretty old – equilibrium theory itself. People still talk about equilibrium theory, and they point to this study as one that showed a system that, more or less, accorded with the theory. So yeah, it is cited for those three reasons: as experiments, with respect to the equilibrium theory and with respect to development of community structure during community assembly.
HS: Today, 47 years after the paper was published, would you say its main conclusion still holds true, more-or-less?
DS: For the system, yes. I wrote a paper that was published in Science, where I looked in some detail at which species were causing the turnover etc. That’s sort of my overview of the whole project, and I think that it’s quite accurate. But I would love to go back now, and see if I see anything that causes me to change my mind.
HS: That leads into the next question I want to ask you – if you were to redo this study today, would you do anything differently, given the advances in technology and statistical techniques, changes in theory etc.?
DS: No, I wouldn’t do anything differently. As far as statistical techniques go – there is not a huge amount of statistics in it. I was an early user of computers, before there were personal computers. I was using a MainFrame to keep backing the data and I used the computer extensively in simulations both for the model (Paper 3) and a few subsequent papers. I guess if there was one thing I would do differently – it’s not differently, but something I try to learn more of myself – I knew which species were which, but I didn’t know a huge amount about the biology of many of them. And in some cases, no one knows about the biology, For example, what does some species of beetle eat – is it eating leaves, is it eating detritus, is it eating other insects etc. That would have been of interest, and if I had the time and I could get help, I would do some of that kind of work. But, generally speaking, I would conduct the study it the same way if I did it today.
HS: What about the fumigation of the islands? Would you do it the same way?
DS: That, I don’t know. We tried a number of things, and it was technically not easy, and there may well be better ways to use fumigants. There’s also a legal issue now about using Methyl Bromide, and also a legal issue about damaging mangroves in Florida. So, there’d be permitting issues that I didn’t have to deal with then. But it worked then you know. It worked the way we did it. If there is a better way I would use it, but I don’t know of a better way now.
HS: Since you mentioned computers, how did you draw the figures for this paper? Were they all drawn by hand?
DS: Oh, do you mean the one showing which species were present and absent on islands? I did that, and I did it by hand. I didn’t have a program then. I ruled paper, and then I typed in the labels. Yes, it was pretty time-consuming. You have to realise that in the 1960s there wasn’t software to do this kind of thing. There was no other way.
HS: It is a huge table. It must have taken a long while to fill in all the cells.
DS: I started that even before I started to write. I knew I was going to need a table like this, and that’s what I did.
HS: Have you ever read this paper after it was published?
DS: Yes, I have. On two occasions. I reread the paper in the wake of papers using those data to try to show community composition and patterns in change of community composition. And I reread the paper, not too long ago, to check something about a couple of species that I was interested in, and exactly when they showed up where. Those are the times I remember.
HS: When you compare this paper to the papers you write now, do you notice any striking differences?
DS: I am sort of aghast that I wrote pretty pretentiously in parts of this, especially in the Introduction. I wouldn’t be quite so florid with my wording today. But you know these were my first papers. The Methods and the Results, I would write pretty similarly, if I wrote it today.
HS: I also wonder if journals today would allow you to include the amount of detailed natural history information you included in this paper.
DS: You may well be correct about that. There is a lot of natural history. It was necessary to explain and rationalise certain things. But today a journal would probably say include it in an online appendix or something. You are right. That’s a good point. It wouldn’t be so easy nowadays, I think.
HS: Would you count this paper as one of your favourites, among all the papers you have written?
DS: I have about 10 favourite papers. I have written 100s of papers, but there are 10 that I’m especially proud of. Some of them I like for their insights. This one, I’m very proud of for a different reason. It represents a lot of really good fieldwork that led to a serious test of a very important hypothesis. So, it is one of my favourite papers.
HS: What kind of impact did publishing this series of papers have on your career?
DS: I’m so old, but I can remember back to the years when I was trying to get a job. It wasn’t hard to get a job then. There wasn’t so much competition for every space. But certainly having been Ed Wilson’s student – and Ed was already pretty well known – and being able to give, as a job seminar, a talk about this work, certainly helped. I applied for a job and they offered me the job. I think it certainly helped me to get my first job but it probably wasn’t too crucial beyond that. But of course, I have only had two jobs! I was at Florida State for 29 years, and now I’ve been at Tennessee for almost 19.
HS: This was the first experimental test of the Island Biogeography Theory. Were there other experimental tests after yours?
DS: Yes, I think so. One was by Jorge Rey at Florida State university. I would say that’s probably the main one, but there were others that sort of tested it. Usually there wasn’t something as clear as a defaunation. There were a number of other tests using microcosms, e.g. people put out bottles of water and watched them being colonised.
HS: What would you say to a student who is about to read this paper today? What should he or she takeaway from this paper written 47 years ago?
DS: Wow, that too is an interesting question. Well, I might have them read it for two different reasons. One is for all the biology in it, and the relationship of that biology to species turnover, and extinction of small populations. That would be one reason I would have them read it. That would be the same reason for which I would have them read it 47 years ago. The other reason might be to stress the importance of doing extensive empirical work, and how you can get a lot of information from real empirical work in addition to theoretical work.