In a paper published in Ecology in 1973, Michael Rosenzweig presented the results on one of the first habitat selection experiments in the field. Rosenzweig’s results indicated that differences in habitat preferences allow a pair of desert rodents to coexist. Forty-three years after the paper was published, I asked Michael Rosenzweig about his motivation to do this study, memories of field work and his reflections on the study’s current standing.
Citation: Rosenzweig, M. L. (1973). Habitat selection experiments with a pair of coexisting heteromyid rodent species. Ecology, 54(1), 111-117.
Date of interview: Questions sent by email on 4th September, 2016; responses received by email on 19th October 2017.
Hari Sridhar: How did you get interested in studying desert rodent communities, and what was the specific motivation for this piece of work?
Michael Rosenzweig: My mentor, the late Robert MacArthur, hired me to help him with some bird censuses and habitat measurements in Arizona in 1962 (when I was a PhD student at the University of Pennsylvania). I fell in love with the desert and its animals. Relating birds to habitat had not worked out very well, but it seemed to me that mammals might work a lot better. They did. And the work (starting in 1966) suggested that we should be able to manipulate the habitat to find out whether the correlations we were seeing reflected cause and effect.
HS: In the Introduction of this paper you say “Knowledge of habitat selection will contribute to the design of future research on such problems” [i.e. understanding the mechanics of competitive coexistence in desert rodents]. Could you reflect on the impact this study had in the design of future research on competitive coexistence?
MR: I believe the most important influence of the paper to be a demonstration that it is possible to perform field experiments with terrestrial vertebrates. Before that, investigators and funding agencies had believed the opposite. The paper also influenced research on American desert mammals. People began to assume that it made sense to look for habitat relationships. And we were able, with Zvika Abramsky, to establish a research program in Israel that emphasized experimentation.
HS: You say arid and semiarid vegetation “can be modified by small groups of workers with almost no equipment”. Could you give us a sense of how many people were involved in the preparation and setting up of these experimental plots?
MR: We were a team of four. We used surveyors’ tape measures and a small chain saw.
HS: You thank “Mr. and Mrs. Caroll Peabody [who] provided the facilities of Mile-Hi, Ramsey Canyon, Arizona”. Could you tell us what these facilities were?
MR: Carroll and Joan Peabody owned the Mile Hi, 20 acres of a well-watered canyon in the Huachuca Mountains of SE Arizona. The Huachucas (almost all in the USA) are the northernmost outpost of Mexico’s Sierra Madre Occidental. An immense diversity of birds nest there. Carroll, who was a builder, put together a cluster of three cabins intended for birders. As I am a twitcher too, I was allowed to rent two of the cabins for my family and my students during a number of summers, displacing some birders by virtue of our small mammal work. It was cooler by 5 degrees C than the valley floor on which we worked, and it had shade and picnic tables on which we could process our morning’s catch. We also stored our animals out of the heat of the valley before returning them to the desert in the evening. I am proud to say that the Peabodys gave this property to the Nature Conservancy, an event that I provided the initial impetus for. The Mile Hi plus an adjoining property now constitute one of the Arizona Nature Conservancy’s crown jewels.
HS: Could you tell us who the people are who feature in the photographs of Figure 2? Would you know the dates when these photos were taken and who took them? Also, what was the rationale behind the codes you used for the sites (e.g. X6W, X5L)?
MR: Dr. Barbara Smigel, David Camarow, the late Tom Smigel and someone who covered his face! They were students and participants on the team. The codes have no scientific meaning; they just allowed us to find the plots repeatedly. I took these pictures with a Yashica SLR during the work itself (summer 1971). It was already a bit difficult to get 35mm black-and-white film if you were not near a professional photo store. Give me a day and I bet I would be able to find the original negatives.
HS: In what ways have these sites changed from the time you worked there for this study? When was the last time you visited these sites? Do you continue to work in these sites? Is it still owned by the Kern County Land Company?
MR: I doubt that the Kern County Land Company retains any ownership of these sites, but I have not revisited for decades. I left when the continuity of our sites was threatened by new suburban-style housing developments and their infrastructure.
HS: You say “habitat tailoring is concerned with necessary habitat features. Compiling a list of sufficient features may require laboratory simulation of the environment”. Did such “laboratory simulation” happen subsequent to this study?
MR: No, my attention was drawn instead to density-dependent habitat selection.
HS: Why was only P. penicillatus tagged on both ears?
MR: P. penicillatus (now Chaetodipus penicillatus) would scratch out its ear tags. It took a while, so, with two tags on an individual, we had a good chance of replacing the ear tag before the identity of the animal was lost.
HS: Could you give us a sense of what your daily routine was when you were doing this study?
MR: Our “day” began in the evening. We opened the live traps and baited them. We ran the trap lines very early the next morning (to prevent the sun from having the chance to kill any captured animals). Traps that had not caught a rodent were closed for the day. We took the captures back to the canyon where we identified, measured, weighed and sexed them. In the evening we returned each animal back to the trap location where it had been caught. And it was evening and it was morning of one day.
HS: You say “The distribution of P. penicillatus captures thus appears to have been different on augmented plots. Although several explanations of this area possible, I have inadequate data to test any of them. Luckily, the phenomenon is not central to the points in question here and can be postponed for future investigation”. Did this “future investigation” happen subsequent to this study?
MR: I can barely understand what I wrote then. In any case, it was a comment, not a promise. I guess I just wanted to indicate the deficiency in our knowledge. There was no “future investigation.”
HS: How long, approximately, did the writing of this paper take? When and where did you do most of the writing?
MR: Given the figure drawing and the one-month turnaround to get an ms. typed, I guess we spent about three months, maybe four to produce the ms. I wrote it when I was on the faculty at SUNY-Albany (now ‘University of Albany’). I wrote it in my study at home.
HS: How were the figures for this paper made?
MR: We made rough outlines of figures in pencil on graph paper. We taped the graph paper to a drafting surface, then taped a blank piece of vellum on top of the graph. Using India ink, we traced the graph onto the vellum. We added any lettering with a lettering set (India ink again). Each graph required a half-day’s work, most often my work. When the vellum drafts were ready, we had them photographed at a blueprint company. Because of that laborious procedure, we adopted a few rules: no drinking or eating while working; nothing becomes a graph that cannot be conveyed in the text; put everything you can into the figure legends rather than in the graph itself; no color.
HS: Did this paper have a relatively smooth ride through peer-review? Was Ecology the first place it was submitted to?
MR: Yes, Ecology was the first place we submitted it. Reviewers were generous and the paper was quickly accepted.
HS: Did this paper have any kind of direct impact on your career?
MR: Yes, it moved me to consider the opportunities for experimental manipulation whenever thinking about a new project.
HS: Today, 43 years after it was published, would you say that the main conclusions still hold true, more-or-less, especially in relation to the two hypotheses you evaluated for observed habitat selection patterns?
MR: Yes, but with profound improvements made by my colleague Stuart Pimm and my former student Joel Brown. Pimm brought a novel mode of coexistence to light (i.e., feeding on the variance — or shared-preference community organization). Brown applied it to the rodents of southeastern Arizona. But time and again, here and in Israel, we have concluded that predation plays a key role in coexistence, whether shared-preference or otherwise.
HS: If you were to redo this study today, would you change anything, given the advances in technology, theory and statistical techniques?
MR: No, I am happy to say that I would do it the same way. In my work, spectacular technological advances have come in the improvement of computers (which I did not need for this work). Because of them, I have been able to do things that used to be entirely impossible.
HS: In the Discussion, you suggest that predator-exclusion experiments will be useful to further understand habitat selection in these rodents. Were such experiments performed subsequent to this study?
MR: Yes, we have undertaken many predator-exclusion experiments —but in Israel. This work continues under the direction of Dr. Burt Kotler, his students and his colleagues. (Kotler took his Ph.D. with me.)
HS: Have you ever read this paper after it was published? When you compare this paper to papers you write today do you notice any striking differences?
MR: Yes, I have read the paper since it was published. In 1991, I studied the style of expository prose used by journalists, and I adopted it. I stopped writing papers in scientific Prussian syntax and tried to make them as close to conversational as I could. Briefly: simple words; simple, short sentences; active voice wherever possible.
HS: Would you count this paper as a favourite, among all the papers you have written?
MR: A favorite? I think it is in the second rank. What is novel in this paper? Its optimistic approach to field experimentation. And I always thought there was a measure of scientific beauty in its design. But I don’t think it breaks any new ground as far as theory, empirical pattern or large scale application.
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 paper written 43 years ago? Would you add any caveats?
MR: When you undertake research, try to streamline it as much as possible. If you have a choice of projects, give extra points to the project using the fewest gadgets. (I confess that, at about the same time, Barbara Smigel and I were doing studies on dietary preferences in the field and the work involved neutron activation analysis. Neutron activation analysis requires a nuclear reactor! We had to farm it out to one at Pennsylvania State University. Once, they actually allowed me to visit. I hate being remote from my work.)
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