HRC July 2020 Newsletter

Note: This newsletter is the last to be contributed by former HRC Chair Dr. Sharon Kingsland. We appreciate her efforts on behalf of ESA’s historical records.

Forty Years Ago: The Ecology of Infectious Diseases as an Emerging Field
By Sharon Kingsland, Newsletter Editor

The Resolution of Respect appearing in the October issue of the Bulletin reviews the extraordinary career of one of the most important theoretical ecologists of our time, Robert M. May, who died on April 28. As the authors of the Resolution note, May had at least five brilliant careers, starting with theoretical physics in Australia, then moving into ecological sciences with two distinguished academic appointments at Princeton and Oxford University, followed by a fourth career as chief science advisor to the UK government, and finally shifting to the study of the stability of financial systems. May liked to jump into relatively uncrowded fields, where opportunities existed to make important contributions. One of these fields in the 1970s was the ecology of infectious diseases, which May developed in the 1970s and 1980s in collaboration with Roy (later Sir Roy) M. Anderson, who is now Professor of Disease Epidemiology at the School of Public Health, Faculty of Medicine, Imperial College London.

May and Anderson met in the mid-1970s at Silwood Park, the field station of Imperial College about thirty miles from London. While on the faculty at Princeton University, May started spending the summers working at Silwood Park, where Richard Southwood had assembled a brilliant group of ecologists, with links to Oxford University, York University, and to Imperial College’s Centre for Environmental Technology (opened in 1976). Hannah Gay has written a study of the “Silwood circle,” and describes the creative synergies fostered among the ecologists there, which contributed to the expansion of ecology along many fronts. These synergies were fostered by the multi-disciplinary environment at Silwood; Gay’s book highlights especially the agricultural and medical problems studied there. In addition to entomology and ecology, Silwood had experts in tropical agriculture, agricultural pests and pest control, and parasitology. One of the many creative interactions at Silwood was the collaboration of May and Anderson, who created a body of theory in the 1970s and 1980s focused on the ecology of infectious diseases, including studies of emerging diseases such as HIV-AIDS.

May was trained in physics and mathematics and clearly perceived that his physicist’s perspective could offer something of value to ecology (May 1985). But he was also interested in ways that ecological methods could be extended to new kinds of problems, and he was quick to identify ways that ecology could enlarge its scope and applications, especially when it came to understanding pressing problems ranging from conservation of species to the spread of infectious diseases. Anderson was similarly interested in bringing different disciplines into communication with each other. He had done his Ph.D. at Imperial College in 1971 and then joined the faculty there, specializing in parasite ecology. As he noted, since he was trained in a university department that included both ecology and parasitology, the fact that he took an early interest in parasite ecology was no surprise (Anderson 1991). By the late 1960s and early 1970s, approaches and ideas coming from theoretical population ecology, including the work of Robert May, were starting to influence parasitology. As members of the Silwood Circle in the 1970s, May and Anderson embarked on a highly productive collaboration that was a model of creative synthesis of disciplines.

A two-part review article that they co-authored in 1979 on the population biology of infectious diseases gives insight into their interdisciplinary goals and desire to expand the way ecologists thought about their discipline (Anderson and May 1979; May and Anderson 1979). In analyzing host-parasite interactions, they defined “parasite” broadly to include viruses, bacteria, and protozoans, as well as the more conventional helminth and arthropod parasites, a definition that enabled them to engage with a large medical and epidemiological literature. That literature assumed that the host population had a constant value, an assumption that derived, as they explained, from the history of medical interest in human diseases, where population densities were roughly constant on the time scale appropriate to the pathology of most diseases. The ecological literature, on the other hand, suggested that parasites could depress or regulate the host population, analogous to the way that predators regulated prey populations. Weaving these two strands together, May and Anderson brought an ecological perspective to bear on the general problem of infectious diseases. “Our main goal,” they wrote, “is to help elevate the study of host-parasite population dynamics to its proper place in ecological thinking; parasites (broadly defined) are probably at least as important as the more usually-studied predators and insect parasitoids in regulating natural populations.” As Anderson (1991) later observed, ecology also had a lot to learn from epidemiology: “One of the major lessons epidemiology can teach ecology,” he wrote, “is the value of long-term data records of changes in organism abundance. Such data provides an excellent template against which to test ideas concerning the factors that determine population size.”

In a study of an important 1981 paper by Anderson and May that analyzed the population dynamics of microparasites and their hosts in greater detail, J. A. P. Heesterbeek and M. G. Roberts (2015) commented that relaxing the assumption of a constant host population was not only a “natural step” when coming to the problem from the ecological side, but it also “opened the way to asking new questions about infectious disease dynamics and studying a much richer set of observed phenomena. Once taken, these steps also turned out to be essential for understanding infectious disease dynamics in human populations.” Heesterbeek and Roberts also noted the importance of collaboration across disciplines: “In contrast to the situation so far where researchers worked mainly in isolation, Anderson and May collaborated in larger groups with biologists and mathematicians, thereby establishing and educating the first real generation of dedicated epidemiological modellers.”

While introducing a special issue on “Conservation and Disease” from a symposium held at the first annual meeting of the newly formed Society for Conservation Biology in the mid-1980s, May reflected on the lack of attention that ecologists had given to the way diseases could affect the distribution and abundance of animals and plants. The subject of disease ecology, he noted, was still largely missing from ecology textbooks. Ecologists tended to favor larger four and six-legged predators, the small size of pathogens made them hard to study, and veterinarians and wildlife managers focused on individual sick animals and not population dynamics. But times were changing, and he perceived an upsurge in interest in disease ecology. May also realized that the field he and Anderson had helped to develop had important consequences for conservation biology, especially the design of natural parks and refuges. It was highly appropriate that the Society should choose this topic for a symposium at its first annual meeting (published in Conservation Biology, 1988, vol. 2).

In an interview conducted in 2014 at an EMBO (European Molecular Biology Organization) Members Meeting in Heidelberg, Germany, May talked about how he approached the task of getting into fields at their early stages, when they were not too crowded, but where there were interesting problems that had not attracted as much attention as he thought they deserved. When he got into something new, it was his habit not to read too much about it at first, but to read just enough to get a grasp of the problem, and then think about how he would go about understanding it better. As he explained, he tried to learn about the “what” questions, but did not spend much effort on what were the tentative “why” questions. “If you read too much about what the current state of progress is, on both the ‘what’ and the ‘why’, it will tend to channel your thinking. If you want to come to it from first principles and ask ‘what can we see there and why is it like that?’ it’s probably not a good idea to read up on what other people have said on that, until you’ve got to the point where you’ve had such ideas as you think might be useful. And then, if you’ve got any sense, you will turn round and carefully and thoughtfully and respectfully read all the things that other people have suggested about the ‘why’.” The last step was essential to determine if your ideas were really new. He added that some scientists working in the field of infectious diseases who were citing Anderson and May’s work, along with others’ work, appeared not to have read the publications they were citing! (Interview by Barry Whyte, “Part I. The practice of science: focus on Lord Robert May,” EMBO Excellence in Life Sciences channel on YouTube.)

Literature cited
Anderson, R.M. 1991. Populations and infectious diseases: ecology or epidemiology? J. Anim. Ecol. 60:1-50.

Anderson, R. M., and R. M. May. 1979. Population biology of infectious diseases: Part I. Nature 280:361-367.

Gay, Hannah. 2013. The Silwood Circle: a history of ecology and the making of scientific careers in late twentieth-century Britain. London: Imperial College Press.

Heesterbeek, J.A.P., and M.G. Roberts. 2015. How mathematical epidemiology became a field of biology: a commentary on Anderson and May (1981) ‘The population dynamics of microparasites and their invertebrate hosts. Phil. Trans. Roy. Soc. B 370:2014007.

May, Robert M. 1986. The search for patterns in the balance of nature: advances and retreats. Ecology 67(5):1115-1126.

May, Robert M. 1988. Conservation and disease. Conservation Biology 2(1):28-30.

May, R. M., and R. M. Anderson. 1979. Population biology of infectious diseases: Part II. Nature 280:455-461.

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