Robert M. May (1936–2020)

Robert M. (Bob) May died on April 28th this year after a period of failing health. Over five decades, his work transformed mathematical ecology by posing new questions and introducing analytical approaches adapted from his training and early research in physics. Somewhat ironically, the elegant abstraction of his models increased the relevance of ecological theory to a broad range of practical issues in fields as diverse as conservation, epidemiology and even economics and stimulated new lines of empirical work. This happened because the models led to insights that changed the way ecologists think. Often, the change began with a demonstration that some well-established principle might not be true; for example, the idea that complex ecosystems with many competitive and exploitative connections among species will be more stable — i.e., more likely to recover from disturbance — than simpler systems with fewer connections. May’s models from the early 1970s, showing that the opposite would be more likely under many circumstances, called attention to the importance of these and other parameters of ecological community structure that are expected to affect a community’s dynamics and resilience. Those parameters — e.g. the quantitative structures of food webs — then became objects of intense theoretical and empirical interest. Throughout his long career, May presented his findings with dazzling clarity and as lessons in how they follow from open, rigorous thought about how a question should be framed and analyzed. He also collaborated with scores of extremely talented colleagues and students, including other pioneers of mathematical ecology in the 1970s. In this way, he influenced not just the substance but also the practice of ecology on many levels, and in many contexts, and was honored in many different ways as one of the discipline’s most influential figures ever. Robert McCredie May was born in Sydney, Australia in 1936 and from childhood was fascinated by puzzles and competitive games, both athletic and intellectual. For example, he excelled at ping-pong, and helped an outstanding Sydney Boys High School debate team vanquish all of its rival schools. (Late in life he recalled his debating experience as critical training for everything he would accomplish as an adult.) Academically, May was inspired by many outstanding teachers, especially in science. At the University of Sydney (1952–1956) he studied chemical engineering, physics, and both pure and applied mathematics, to the horror of advisors who insisted he should specialize. There was also a great deal of chess and snooker. For his PhD, also at Sydney, May joined the group of Max Robert (Robbie) Schafroth, which was pursuing the idea that a charged gas of bosons could be a superconductor. At the time, there was still no successful theory of superconductivity. May’s thesis project was to model a mechanism, hypothesized by Schafroth and his colleagues at Sydney, to get pairs of electrons (which are fermions) to bind together and behave effectively as bosons. In 1957, Bardeen, Cooper and Schrieffer published an alternative explanation (the BCS theory), which explained the critical observations and won the Nobel Prize in 1972. May finished his thesis on other aspects of the superconductivity problem the following year and prepared to follow Schafroth to Geneva where he had been offered a distinguished chair in theoretical physics. But before that could happen, Schafroth was killed in a small-plane accident. May was devastated and “just … wanted to get out of Sydney as soon as I could.” (This and many of the subsequent quotes are from a 2011 interview with Robyn Williams which can be found as a transcript on the Australian Academy of Science website (https://bit.ly/2WKz77N) and will soon be rebroadcast on the ABC Science Show.) May’s other mentors in the theoretical physics group that had been assembled by Harry Messel (John Blatt and Stuart Butler) arranged for him to do a postdoc at Harvard with Max Krook, a mathematician and astrophysicist. There, May “fell in with a very happy small group of friends” made up of graduate students and other faculty in the division, turned down an assistant professorship because he planned to return to Australia, and met his future wife Judith Feiner on a blind double date that played out as classic rom-com. At the end of 1961, May returned to Sydney as a Senior Lecturer in Physics. He was soon promoted to Reader and then in 1969 to Professor. At that time, he was also becoming increasingly concerned about human impacts on the environment, as were millions of people everywhere — the first Earth Day was April 22, 1970. May’s growing interest in issues related to ecology was noted by Messel, who encouraged him to “get into bringing physics into biology.” On reading Kenneth Watt’s book Ecology and Resource Management (1968), May discovered that professional ecologists shared a belief that more complex ecosystems, “with more species and more interactions among them … would by virtue of that complexity, be more stable.” Watt’s presentation of the argument admitted that its conclusion could be seen as counterintuitive. May’s reaction was to agree, and to realize that an obvious test of the argument would be to compare dynamical models with different numbers of species and different strengths of interaction among them. He attempted this and found that for a given average strength of interaction, increasing the number of species will usually make the ecosystem more likely to collapse (to a smaller number of species) following a disturbance. May took this result to Charles Birch, a colleague in biology who, though not a theorist, was very well prepared to appreciate its significance. Birch suggested he send it to Watt, who wrote back saying “this is a milestone in ecology.” Not only was a specific bit of dogma thereby shown to rest on shaky foundations, but as this sank in, the entire outlook of population ecology would begin to transition away from a primary focus on external disturbances followed by returns to equilibria, and toward a focus on internally generated dynamics driving potentially endless episodes of community readjustment. In early 1971, May was about to set off on a sabbatical to the Plasma Physics Research Laboratories at Culham in the UK, and from there to the Institute for Advanced Study at Princeton in the US. When Charles Birch learned of this plan, he arranged for May to meet the ecologists Richard Southwood of the Imperial College field station at Silwood Park while in the UK, and Robert MacArthur of Princeton University’s Department of Biology while in the US. Birch’s inspired matchmaking changed May’s life and the history of ecology. At Culham, May gave a talk that — as he privately admitted to a colleague — might be his last in physics. He also gave a talk at Silwood Park and was greatly impressed by many researchers he met there, including Southwood (a visionary insect ecologist with broad interests including populations that showed dramatic year-to-year fluctuations). He would soon begin extensive collaborations with many of these scientists, and thereby get to know both the substance and the culture of ecology from the inside. In the fall of 1971, May arrived in Princeton to work at the Institute for Advanced Study with an old friend from Harvard, the astrophysicist John Bahcall. As arranged by Birch, he made an appointment with Robert MacArthur, who was an influential theorist and leader of a nascent ecology group in Biology. Although only in his early 40s, MacArthur was dying of cancer and working hard to finish various projects including his book Geographical Ecology (1972). After agreeing on a time to meet with May, MacArthur asked a young assistant professor, Henry Horn, to rescue him from what he clearly feared might be a tedious encounter with an enthusiastic but hopelessly misguided physics guy. “After ten minutes I want you to knock on the door and say I have an urgent phone call.” Horn did as instructed, but MacArthur quickly returned and continued his conversation with May for another two hours. At the end MacArthur said “I’m going to be extinct in about a year and I’m very keen to find my successor; might you be interested in coming here to take my professorship?” May replied that he liked his position in Australia and planned to return. MacArthur asked him to give a seminar so that people in Biology could get to know him, and that led to a formal offer from the chair (John Bonner), which May also turned down. MacArthur had launched the highly regarded Princeton Monographs in Population Biology with his and E.O. Wilson’s Theory of Island Biogeography in 1967. As the editor of the series, he urged May to write up his work on stability and complexity at Monograph length, which May did on his return to Sydney. Stability and Complexity in Model Ecosystems was published in 1973, shortly after MacArthur’s death. While working on the book, May began to understand that he had stumbled into ecology’s “golden age for theory” and would not return to physics in a serious way. He was offered an ecology position at the Australian National University in Canberra, which he might have accepted, except for Judith’s observation that Princeton was an opportunity that might not come again. So May called Bonner, and as he recalled the conversation many years later, it went like this. May: “Have you fixed on Robert’s successor or are you still looking? I’ve changed my mind. I’d like to do it.” Bonner: “Great.” And that was that. No discussion of salary, benefits, responsibilities or anything else. The Mays moved to Princeton and anchored the ecology group for 16 years. Bob took over as editor of the Monographs in Population Biology and de facto leader of the ecology group which grew in size and strength very largely through his advocacy and example. He mostly avoided administrative entanglements, but made an exception when he was asked to lead the University Research Board — equivalent to being a vice president for research at most universities today. At Princeton, at that time, it was a part-time job that did not interfere with research and teaching. This experience in high-level administration that May gained over 11 years proved invaluable during his service, much later, in the Royal Society and as adviser to the UK government. Meanwhile Judith developed an independent career as a professional science editor with Princeton University Press. Princeton was an ideal environment for May’s development as an ecologist: in part because he was surrounded by naturalists and experimentalists with knowledge and skill sets very different from his own, as well as outstanding practitioners of all the other disciplines of modern biology; in part because the university was a magnet for visitors; and because it was led by talented administrators who supported the organic growth of academic communities. May also further strengthened his ties with the British ecology powerhouse headquartered at Silwood Park, by spending at least a month there every summer and collaborating extensively with Roy Anderson, Michael Hassell, John Lawton and many others. In his first decade at Princeton, May established a number of research themes and collaborations that would continue through the rest of his career. For example, he discovered the ‘chaotic’ dynamic complexities that can emerge from very simple models for populations with discrete, non-overlapping generations, and published several seminal papers in the 1970s that contributed to the emergence of chaos theory as a multidisciplinary field in its own right. He became interested in a range of questions about the diversity and abundance of species within ecosystems and over the Earth as a whole, including how to estimate biodiversity with very limited sampling. He began what would become an immense body of work on the dynamics of host–parasite and host–pathogen systems, culminating in his 1991 book with Anderson, Infectious Diseases of Humans: Dynamics and Control. And he addressed problems involving human impacts on natural ecosystems, such as fisheries management. Many of these studies strongly influenced future work in their fields, by showing how simple dynamical models that are intentionally unrealistic in some respects can illuminate complex data sets — such as patterns of infection over time — by identifying the structural features and other key parameters of the system that generate and guide its behavior. May’s guidance of the Princeton ecology group was also highly dynamic, literally, in that opportunities for competitive sport were unlimited. A typical initiative was his organization of informal Friday afternoon soccer games that everyone in Eno Hall (a charmingly dumpy little building that was then the group’s home) was expected to join – students at all levels, faculty, visitors, everyone, regardless of skill or experience. Some grumbled, but most eventually got the point, which was to blur the lines between novices and masters, between work and play, between thinking and acting. May also initiated the Eno Invitational Mile Run, which was held twice each year, and has continued. Everyone was expected to participate, of course. Visits by fast seminar speakers were often scheduled to coincide with a running (the honorarium was tiny, but you could take home a Princeton coffee mug or other symbolic prize), and data on everyone’s times were curated by Horn, according to whom “over 14 years, Bob’s average time and standard deviation for the mile were 5:45 ± 13 seconds … impressive!” Richard Southwood moved to Oxford University in 1979, as Head of the Zoology Department, with a mandate to rebuild a distinguished faculty that had been thinned by deaths and retirements. May was eventually persuaded to join, as a Royal Society Research Professor. The deciding factor was not any dissatisfaction with Princeton, but instead that “Judith and I felt that … we should really think about doing something different … while we still had the energy.” Judith took up an editorial position with Oxford University Press and they moved in 1988. At Oxford, May continued many of the collaborations and research themes that he had begun while at Princeton, and also initiated an important new thread in association with George Sugihara who had done his PhD with May in the early 1980s. In 1990, Sugihara and May published a landmark paper describing a technique called ‘non-linear forecasting’ that could distinguish the signals of deterministic chaos from those of measurement error in population time-series data. This work was soon recognized as relevant to financial systems as well as ecosystems, and Sugihara was recruited to Deutsche Bank (1997–2002) on leave from his academic position at the Scripps Institute of Oceanography. Meanwhile May had taken a leave from Zoology (1995–2000) to serve as Chief Scientific Advisor to the UK government and Head of the Office of Science and Technology, under prime ministers John Major and Tony Blair. After that, he became President of the Royal Society (2000–2005). His responsibilities in those positions often involved starkly non-academic, real-world issues such as the foot-and-mouth disease epidemic, SARS and climate initiatives. In 2006, May participated in an interdisciplinary project organized by the US National Academies and the Federal Reserve Bank of New York to “explore parallels between systemic risk in the financial sector and various domains in engineering, ecology and other fields.” Sugihara and Simon Levin (May’s successor at Princeton) also participated. The project’s report was published in late 2007, and the three ecologists reviewed it in a Nature piece titled “Ecology for bankers”, published seven months before the September 2008 collapse of the Lehman Brothers investment bank, which triggered the Great Recession. Their review notes that fisheries managers have learned the hard way why single-species analyses are often inadequate: they don’t account for ecosystem-level processes that can make a population more vulnerable to collapse than is apparent when its world is taken as given. In a similar way, conventional risk assessments of individual firms may fail to identify the full extent of their real vulnerabilities, because those firms are also embedded, analogously to species, in a complex web of exchange relations that was not designed. This and subsequent comparative studies of instability in different kinds of complex systems have reciprocally illuminated ecology as well as finance and have stimulated work on even more fundamental questions about establishing causal linkages in natural systems from observational time-series data. In 2012, Sugihara, May and five coauthors published a novel approach to “Detecting causality in complex ecosystems”. Thus, May’s career not only played a leading role in bringing key elements of the outlook and methodology of physics into biology, as foreseen by Messel, but it also brought biology, as thereby enhanced, into economics. May was honored in every conceivable way for the originality and importance of his many and diverse contributions to science and its application, by awards, medals, election to memberships and honorary degrees from learned societies and universities; and by prestigious special prizes such as the Balzan, the Blue Planet and the Crafoord (‘ecology’s Nobel’). His contributions to the civic life of the UK were also recognized by a knighthood and appointment to the Order of Merit. May insisted often and emphatically that the secret of his extraordinary success was that he had been “extraordinarily lucky” — that he had somehow managed to be in the right places, at the right times, and to meet an enormous number of the right people, and in particular, Judith. Those who had the reciprocal good luck to know and work with him knew that their world was vastly larger and better because of his presence in it. And thanks to his engaging and lucid writing (and his enormous output) he will remain effectively present for many future generations of scientists and scholars.