Ecology John L. Harper
by
Roy Turkington
  • LAST REVIEWED: 16 February 2016
  • LAST MODIFIED: 27 July 2016
  • DOI: 10.1093/obo/9780199830060-0135

Introduction

Professor John Lander Harper CBE, FRS (b. May 27, 1925–d. March 22, 2009) revolutionized plant ecology and had perhaps a greater impact on its development as a modern science than any other ecologist in the 20th century. Raised on a farm in Rugby, England, Harper did his undergraduate and graduate degrees in Oxford. He then spent nine years as a lecturer at the Department of Agriculture, and, in 1960, he was appointed head of agricultural botany at the University College of North Wales, Bangor. He served as president of the British Ecological Society in 1966–1967 and of the European Society for Evolutionary Biology from 1993 to 1995; he was elected a Fellow of the Royal Society in 1978. He taught us an entirely new discipline and an entirely new way to study plants by changing the way we think about vegetation; instead of being relatively static, vegetation was viewed as a dynamic system of plant populations, in a state of continuous flux, based on birth and deaths of individuals. Almost single-handedly he pioneered the establishment of the field of plant population ecology. By bringing population biology and experimental approaches to the forefront of plant ecology, he linked demography and selection and, therefore, ecology and evolution. Harper’s ideas are now so central to plant ecology that they have become basic to our way of thinking. He began to ask questions about plant populations that zoologists had been asking about animal populations since at least the 1930s. Although faced with the dual difficulties of plant plasticity and of how to define “an individual plant,” Harper not only found ways of answering these questions, but also he presented the answers in a way that convinced us that plants were worthy of study; furthermore, plant populations were often easier to study than animal populations because they “stand still and wait to be counted” (Harper 1977, p. 515, cited under Population Biology of Plants). The repertoire of Harperian ecology included seed production, seed banks, seed dispersal, seed dormancy, seed-soil interactions, seedling recruitment, effects of neighbors, interference, population regulation, plant-animal interactions, dynamics of plant populations, demography, population evolution, resource allocation, and plant life histories. His upbringing on a farm and agricultural background are clearly reflected in the subjects used in much of his research—crop plants, grasses, and weeds—and the pasture at Henfaes, North Wales, served as the study site for at least ten graduate students and overseas visitors. In 1977 Harper published his monumental Population Biology of Plants.

Biography

A detailed profile of Harper’s life until 1985 is provided in Sagar 1985 and in obituaries in Franco, et al. 2009; Turkington 2009; and Cavers 2009). John Lander Harper was born on May 27, 1925, into a farming family. He was educated at Lawrence Sheriff School, Rugby, where, under the enthusiastic leadership of Wilfred Kings, he developed a deep enthusiasm for natural history. At the age of thirteen, Harper observed and counted buttercups along a transect across an undulating pasture on his father’s farm (Harper 1989). He noted that different species of buttercups grew in different parts of the pasture (personal communication). In 1943 he entered Magdalen College, Oxford, and graduated with a first class honors in botany in 1946, followed by a master’s degree and a doctorate in philosophy in 1950, completed under the supervision of Dr. J. L. Harley. Harper was then appointed as a demonstrator at Oxford University in 1951 and personally acknowledges that G. E. Blackman was “exceptionally supportive in helping me to acquire my own group of D. Phil. students; G. R. Sagar and I. H. McNaughton came to me from the Oxford Botany Department and John Clatworthy came from Rhodesia as a Rhodes Scholar” (J. L. Harper, unpublished memoirs; provided by Claire, his daughter). From 1953 to 1959 he was lecturer in the Department of Agriculture and, after a sabbatical (1959–1960) as a Rockefeller Foundation fellow at the University of California, Davis, he was appointed head of agricultural botany at the University College of North Wales (UCNW), Bangor. In 1967 the Departments of Botany and Agricultural Botany merged and Harper became head of the new School of Plant Biology. He retained that position until 1982. At this time he was also president of the British Ecological Society (BES) (1966–1967). The School of Plant Biology at Bangor became the mecca for plant population biologists. It became identified with almost everything new emerging in the field of plant population ecology, attracting graduate students and visitors from all over the world. In 1982 Harper became emeritus professor at UCNW, but he continued as head of “The Unit”—the Unit of Population Biology, School of Plant Biology, UCNW. John Harper served as president of the European Society for Evolutionary Biology from 1993 to 1995, and he served as a visiting professor at the University of Exeter in 1998.

  • Cavers, Paul. 2009. Professor John L. Harper: The Canadian connections. Canadian Botanical Association Bulletin 42:84–85.

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    This article catalogues John Harper’s Canadian connections with graduate students, postdocs, visiting scientists, and numerous undergraduate exchange students. The article also documents a few amusing and/or challenging incidences from this cross-Atlantic connection.

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  • Franco, Miguel, José Sarukhán, and Rodolfo Dirzo. 2009. A Darwinian plant ecologist, John Lander Harper CBE FRS, 1925–2009. In Memories of John L. Harper: A remembrance by his friends, students, and colleagues. 2d ed. Edited by Glenn R. Matlack, 98–100. Bangor, UK: JPB.

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    This online resource written by three of Harper’s graduate students provides an overview of Harper’s academic career and influence, and how this influence has spread into successive generations of Mexican students, contributing to the study and conservation of Mexico’s biodiversity.

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  • Harper, John L. 1989. Plant demography: A citation classic commentary on Population Biology of Plants by John L. Harper. Current Contents/Agriculture, Biology and Environmental Sciences 5:14.

    DOI: 10.1111/j.1365-2745.2009.01528.xSave Citation »Export Citation »E-mail Citation »

    In this one-page article, Harper outlines why the time was ripe for his writing of Plant Population Biology; he notes that “plant ecology was in the doldrums; it was rarely experimental and could not link easily with evolutionary theory” (p. 14). At the time of writing this article, the book had been cited in more than 1,660 publications.

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  • Sagar, Geoff R. 1985. Profile of John L. Harper. In Studies of plant demography: A festschrift for John L. Harper. Edited by James White, xix–xxv. London: Academic Press.

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    This profile was written by one of Harper’s early graduate students and long-time friend and colleague. Thus it provides extra details of Harper’s early enthusiasm for natural history, his early academic achievements, and the history of the development of the School of Plant Biology in North Wales.

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  • Turkington, Roy. 2009. Obituary: Professor John L. Harper, FRS CBE, 1925–2009. Journal of Ecology 97:835–837.

    DOI: 10.1890/0012-9623-91.1.9Save Citation »Export Citation »E-mail Citation »

    This tribute to John Harper was written by a former graduate student and provides a description of Harper’s personality, the development of his research approach, his family life, responses of those around him in Bangor, and a number of direct “Harperian” quotations. Reprinted in Bulletin of the Ecological Society of America 91 (2010): 9–13.

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Awards and Service

John Harper was made a fellow of the Royal Society in 1978 (Anonymous 1978), an honorary associate of the Swedish Society for Phytogeography in 1981 and a foreign associate of the US National Academy of Sciences in 1981. In 1984 he was recognized by the Ecological Society of America as “eminent ecologist” (Werner 1985). Also in 1984, the University of Sussex awarded him an honorary doctorate (D.Sc.), and in 1989 he was made an officer of the Order of the British Empire (CBE). The Royal Society awarded John Harper the Darwin medal (Anonymous 1990). The National University of Mexico awarded him an honorary doctorate 1996. He was given the Millennium Botany Award by the International Botanical Congress in 1999 and the Marsh Award by the British Ecological Society in 2000 (Anonymous 2000). From 1971 to 1998 John Harper served in various advisory roles for bodies, including the Natural Environment Research Council, the Royal Society, the Agricultural and Food Research Council, the Comitė du Direction, C.E.P.E. (C.N.R.S.), the Joint Nature Conservation Committee, and as a Trustee of the British Museum of Natural History. He also held various editorial roles, including editor in chief of Agroecosystems (1974–1981), coeditor of Oecologia (1982–1994), assistant editor of Philosophical Transactions of the Royal Society, (1990–1992), assistant editor of Proceedings of the Royal Society (1980–1982), and editor of Proceedings of the Royal Society of London, Series B (1992–1998).

  • Anonymous. 1978. Harper, John Lander (EC/1978/12). Royal Society of London.

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    Part of the citation states that John Harper was “Distinguished for his researches in plant ecology, especially on the autecology of selected species and on the establishment, interaction and competition of closely related species. Hiw (sic) work is characterized by acute observations, ingenious but simple field and laboratory experiments and rigorous statistical appraisal.”

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  • Anonymous. 1990. The Darwin medal: Awarded to J. L. Harper by the Royal Society of London. Royal Society News 5:4.

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    Part of the citation reads: “By his breadth, originality and imaginative experimentation he has become a world leader in the field of plant ecology” (p. 4).

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  • Anonymous. 2000. Marsh Award for ecology: Awarded to J. L. Harper by the British Ecological Society. Bulletin of the British Ecological Society 31:15.

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    This award was given for “pioneering a whole new field of scientific endeavor: the population biology of plants [and] the development of the science of plant ecology” (p. 15).

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  • Werner, Patricia. 1985. Eminent ecologist citation: Awarded to J. L. Harper by the Ecological Society of America. Bulletin of the Ecological Society of America 66:20–21.

    DOI: 10.2307/20166424Save Citation »Export Citation »E-mail Citation »

    Part of the citation states that John Harper “revolutionized plant ecology. . . no one has had more influence on plant population ecology during the period of its coming of age” (p. 20). Available online for purchase.

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Academic Development

Many circumstances and individuals influenced Harper’s academic development. Harper publically recognized the influence of Wilfred Kings, his high school biology teacher, in the dedication of Population Biology of Plants: “to W. K., Teacher and Friend.” At a much broader level he was profoundly influenced by Charles Darwin and no fewer than fifteen direct quotations from The Origin of Species are found in Harper’s presidential address to the British Ecological Society—A Darwinian Approach to Plant Ecology (Harper 1967, cited under Background Development: University College of North Wales (UCNW), Bangor and Evolutionary Ecology). During his tenure at Oxford, Harper was probably most influenced by G. E. Blackman and he developed his distinctive style of plant ecological research that incorporated natural selection, experiments and theory. His development was also shaped by Arthur G. Tansley’s manner, albeit short term, of doing experiments (Tansley 1913), and Alex S. Watt’s extended field observations and detailed analysis of proximal ecological events involving the monitoring of individuals (Watt 1947). Harper was also influenced by John Maynard Smith’s analysis of evolutionary theory and of the role of sexual reproduction as a crucial factor in evolution and in the survival of species. Harper acknowledges that he had great teachers, Charles Elton and George Varley (Varley 1957), “animal ecologist who gave me great encouragement when the work was viewed by great suspicion by plant ecologists” (Harper 1989, p.14, cited under Biography). And he hails Ledyard Stebbins and Bob Allard, who “both forced me to think as an evolutionist” (p. 14). Often overlooked is the influence of Harper’s departmental colleague in Bangor, Professor Peter Greig-Smith. During the 1960s ecologists actively debated the role of reductionism and holism as tools to understand ecological phenomena. The debate was carried on worldwide, and it took place in a mesocosm in Bangor. John Harper was a strong proponent of an experimental and reductionist approach to ecological research, and Peter Greig-Smith was a quantitative ecologist seeking large-scale patterns in vegetation. As described in Hill 2003 and Matlack 2009, Harper and Greig-Smith engaged in frequent, good-humored debates following departmental seminars, which “were conducted amid legendary clouds of pipe smoke” (Ezcurra 2014). These stimulating, rigorous, and good-natured discussions not only likely sharpened the intellectual abilities of Harper and Greig-Smith, but they also had a deep influence on a generation of Bangorian students. See also the Oxford Bibliographies article by Exequiel Ezcurra “Peter Greig-Smith.”

Background Development

John Harper spent his entire academic career at Oxford and in North Wales. At Oxford he developed his distinctive style of research described earlier, one that incorporated natural selection, experiments, and theory. It was at Oxford that he and his students began to study fine-scale interactions among seeds, seedlings, and their environment. The Oxford years paved the way for an entirely new approach to the study of plant ecology that was to flow from Bangor.

Oxford, Department of Agriculture

While at Oxford during the 1950s Harper, Landragin and Ludwig began a series of studies on the influence of the environment on seed and seedling mortality (Harper, et al. 1955). During this same period, Harper also gave increasing attention to the study of weeds, and from 1953 to 1960 he published ten papers on weeds, particularly Ranunculus spp. (Harper and Sagar 1953) and Plantago spp., and these included some classic ecological papers (Harper 1957, Harper 1960). These early studies produced the nine-paper “the comparative biology” series that began after many rigorous and vigorous discussions among Ian McNaughton, John Clatworthy, and Geoff Sagar together with John Harper. These four individuals were perplexed by the diversity of natural vegetation and why so many species could coexist, often closely related species, especially in light of both Gause’s competitive exclusion principle and because Darwin argued that the severest competition should come from the most similar species (McNaughton and Harper 1960; Harper, et al. 1961; Harper and McNaughton 1962). Before Harper left Oxford he organized the first symposium of the British Ecological Society titled “The Biology of Weeds”; he was editor of the resulting book (Harper 1960, cited under The Biology of Weeds) as well as the author of two chapters (e.g., Harper 1960). Later he presented the keynote address on “Approaches to the Study of Plant Competition” (Harper 1961) at a symposium of the Society for Experimental Biology.

  • Harper, John L. 1957. The ecological significance of dormancy and its importance in weed control. In Proceedings of the IVth International Congress of Crop Protection, Hamburg 1990. Edited by Johannes Krause, 415–420. Brunswick, Germany: International Congress of Crop Protection.

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    This paper set the stage for numerous papers on weed seed dormancy and germination and is still cited.

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  • Harper, John L. 1960. Factors controlling plant numbers. In The biology of weeds. By John L. Harper, 119–132. British Ecological Society Symposium 1. Oxford: Blackwell.

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    Arguably one of the earliest experimental plant ecology papers to give serious attention to density dependent regulation in plant populations, referring specifically to the weedy species Papaver spp. and Agrostemma githago.

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  • Harper, John L. 1961. Approaches to the study of plant competition. In Mechanisms in biological competition. Edited by the Society for Experimental Biology, 1–39. Symposia of the Society for Experimental Biology 15. New York: Academic Press.

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    This paper compares the many and varied methods used by physiologists, agronomists, ecologists, and geneticists to study competition.

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  • Harper, John L., John N. Clatworthy, Ian H. McNaughton, and Geoff R. Sagar. 1961. The evolution and ecology of closely related species living in same area. Evolution 15:209–227.

    DOI: 10.2307/2406081Save Citation »Export Citation »E-mail Citation »

    This sixteen-page essay classic “was finally published in 1961 but not before two prestigious and subsequently reformed British journals had declined to do so, presumably because the treatment was so far removed from the current mainstream of ecological research in the plant sciences” (Sagar 1985, pp. xxi–xxii; cited under Biography).

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  • Harper, John L., Phyllis A. Landragin, and Jerzy W. Ludwig. 1955. The influence of environment on seed and seedling mortality, I: The influence of time of planting on the germination of maize. New Phytologist 54:107–118.

    DOI: 10.1111/j.1469-8137.1955.tb06165.xSave Citation »Export Citation »E-mail Citation »

    This is the first in a series of eight papers showing how micro-scale heterogeneity of the soil surface can act as a filter or sieve allowing some seeds to germinate but preventing others. Maize was used because G. E. Blackman (Unit of Experimental Agronomy, Oxford) was considering its possible use as a crop in Britain.

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  • Harper, John L., and Ian H. McNaughton. 1962. The comparative biology of closely related species living in the same area, VII: Interference between individuals in pure and mixed populations of Papaver species. New Phytologist 61:175–188.

    DOI: 10.1111/j.1469-8137.1962.tb06286.xSave Citation »Export Citation »E-mail Citation »

    This is the first of many studies in which Harper’s lab made use of the de Wit replacement series approach to studying plant “competition” (interference). Unaccountably, de Wit is not cited in the text but his name is included in the list of references. Harper championed this method as a powerful way to experimentally dissect the complexity of plant interference.

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  • Harper, John L., and Geoff R. Sagar. 1953. Some aspects of the ecology of buttercups in permanent grasslands. In Proceedings of the British Weed Control Conference. Edited by British Crop Protection Council, 256–263. Brighton, UK: British Crop Protection Council.

    DOI: 10.1080/00288233.2003.9513557Save Citation »Export Citation »E-mail Citation »

    This paper marked the beginning of Harperian ecology and paved the way for a generation of studies on plant population dynamics. This paper harbors the origins of the Ranunculus work, the Papaver work, and the series on “closely related species living in the same area.”

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  • McNaughton, Ian H., and John L. Harper. 1960. The comparative biology of closely related species living in the same area, I: External breeding barriers between Papaver species. New Phytologist 58:15–26.

    DOI: 10.1111/j.1469-8137.1960.tb06197.xSave Citation »Export Citation »E-mail Citation »

    The first in a series of nine articles that deal with how closely related species could coexist given Gause’s competitive exclusion principle and Darwin’s argument that the severest competition should come from the most similar species. The theoretical and philosophical background to this series is Harper, et al. 1961.

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University College of North Wales (UCNW), Bangor

The Oxford years were productive and they provided an intellectual environment that promoted the development of a foundation for a whole new era of plant ecological thought and research that was to flow from Bangor, much of which is encapsulated in Harper 1964a, Harper 1964b, and Harper 1965 as well as Harper 1967 (also cited under Evolutionary Ecology), Harper 1968 (also cited under Regulation), and Harper 1969. It was from Bangor that many seminal and influential papers were published and to which many graduate students, doctoral graduates, and other visitors, most often from overseas, were attracted. Harper and his lab continued with the Darwinian theme and probed plant population biology with particular emphasis on reproductive allocation, interference, population dynamics, and demography.

  • Harper, John L. 1964a. The individual in the population. Journal of Animal Ecology 33:149–158.

    DOI: 10.2307/2436Save Citation »Export Citation »E-mail Citation »

    This paper brings together some examples of plant interactions that result in changes in the behavior of individuals as they become influenced by the proximity of their neighbors. Available online for purchase.

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  • Harper, John L. 1964b. The nature and consequence of interference amongst plants. In Genetics today: Proceedings of the XIth International Congress of Genetics, The Hague, the Netherlands, September 1963. Vol. 2. Edited by S. J. Geerts, 465–482. Oxford: Pergamon.

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    This paper stresses the need for serious attention to be paid to the ways in which plants may interfere with each other and the consequences of this interference.

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  • Harper, John L. 1965. Establishment, aggression, and cohabitation in weedy species. In The genetics of colonizing species. Edited by Herbert G. Baker and G. Ledyard Stebbins, 243–263. New York: Academic Press.

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    This paper caught the attention of the famous American biologists E. O. Wilson, G. L. Stebbins, Ernst Mayr, and Herbert Baker. This presentation arguably opened Harper’s gateway to the ecological audience in the United States. The paper concludes that germination and seedling establishment are the most important factors for successful spread and resistance to native flora.

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  • Harper, John L. 1967. A Darwinian approach to plant ecology: Presidential address, British Ecological Society. Journal of Ecology 55:247–270.

    DOI: 10.2307/2257876Save Citation »Export Citation »E-mail Citation »

    This enormously influential paper became an instant classic in the ecological literature and inspired an entire generation of plant ecologists. This single paper describes, or introduces, much of Harper’s research career. This paper was listed as “one of the top 100 most influential papers published by the British Ecological Society (1913–2012)” as part of the BES centenary celebrations. Also available in Journal of Applied Ecology 4 (1967): 267–290, and Journal of Animal Ecology 36 (1967): 495–518.

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  • Harper, John L. 1968. The regulation of numbers and mass in plant populations. In Population biology and evolution. Edited by Richard C. Lewontin, 139–158. New York: Syracuse Univ. Press.

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    The key word in this title is “plant.” Harper argues why it is risky to uncritically apply population theory derived for animals, to plants. He also discusses “the individual as a population,” dormancy (which animals don’t really do!), and de Wit methods of studying plant competition and regulation.

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  • Harper, John L. 1969. The role of predation in vegetational diversity. In Diversity and stability in ecological systems: Report of a symposium held May 26–28, 1969. Edited by G. M. Woodwell and H. H. Smith, 48–62. Brookhaven Symposia in Biology 22. Upton, NY: Brookhaven National Laboratory.

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    This paper cautions that just because the world is green does not mean that herbivores are unimportant to plants. Three major types of experiment are described that test the effects of herbivores on vegetation. Also cited under Darwinian and Wallacian Perspectives.

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Research Framework

Throughout his career Harper used his single-authorship papers, which were often published proceedings from international conferences, to develop and present his core scientific framework. Many of these were based on pure scholarship rather than the usual conventional reviews and it is from these papers that his ideas, arguments, and questions were formulated, many of which remain unanswered, and from which Harper’s unique academic research philosophy can easily be identified, namely natural selection (evolutionary ecology), experiments, and theory.

Evolutionary Ecology

Harper’s foundational theme was that Darwin’s theory of evolution by natural selection is an ecological theory and that ecology is evolution in action (Harper 1967, also cited under Background Development: University College of North Wales (UCNW), Bangor; Harper 1983). This is rooted in Darwin’s emphasis on the role that individual differences play in evolution by natural selection (Harper 1964a, cited under Background Development: University College of North Wales (UCNW), Bangor), yet the study of the fate of individual plants was largely ignored. He pioneered a field of study in which the fate of individuals, and the mechanism by which they leave descendants, was paramount.

  • Harper, John L. 1967. A Darwinian approach to plant ecology: Presidential address, British Ecological Society. Journal of Ecology 55:247–270.

    DOI: 10.2307/2257876Save Citation »Export Citation »E-mail Citation »

    Harper develops his foundational theme that Darwin’s theory of evolution by natural selection is an ecological theory. There are at least fifteen quotations from chapters 3 and 4 of Darwin’s Origin of Species, numerous questions are posed, and the paper emphasizes the role that individual differences play in natural selection. Also available in Journal of Applied Ecology 4 (1967): 267–290, and Journal of Animal Ecology 36 (1967): 495–518.

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  • Harper, John L. 1983. A Darwinian plant ecology. In Evolution from molecules to men. Edited by D. Bendall, 323–345. Cambridge, UK: Cambridge Univ. Press.

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    This paper briefly reviews and contrasts the scientific approaches of Darwin and Wallace. Harper commends the early modeling work of Nägeli in the 1870s and Gause, and he applauds the long-term studies of Tamm (and others) who made permanent plots and monitored the fate of individuals.

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Darwinian and Wallacian Perspectives

Studies describing patterns of differentiation in plant populations have been undertaken for more than 250 years. Langlet 1971 cites 111 references that are pre-1900, six of which are from the 1700s. In most cases the processes generating the patterns were largely ignored until the 1960s. Most of this previous work had been dominated by what Harper calls “a Wallacian attitude” (Harper 1977, cited under Population Biology of Plants). Wallace thought of natural selection as primarily a struggle against the physical factors of the environment, such as moisture, temperature, or soil type, with the result that different types of organisms live in different environments. Such studies were important and often clearly demonstrated that micro-evolution occurred over very short distances, often in the presence of extensive gene flow and over relatively short time intervals. In contrast, Darwin emphasized the role of biotic factors, such as competition and herbivory, and sought to understand how so many types of plants (and animals) could coexist and avoid elimination. Harper highlighted this when he wrote “it is therefore rather odd that although it is Darwin’s influence that is usually acknowledged in the development of evolutionary theory, it is a Wallacian attitude that has dominated the study of adaptation in plants” (Harper 1977, p. 750). Key papers with this emphasis on the impact of biotic factors on plant populations are Harper 1969 (cited under Background Development: University College of North Wales (UCNW), Bangor), Turkington and Harper 1979, Burdon 1980, Dirzo and Harper 1982a, and Dirzo and Harper 1982b.

  • Burdon, Jeremy J. 1980. Intra-specific diversity in a natural population of Trifolium repens. Journal of Ecology 68:717–735.

    DOI: 10.2307/2259452Save Citation »Export Citation »E-mail Citation »

    In this paper, fifty clones of Trifolium repens were sampled from the field at Henfaes. They were screened for a number of traits, most of which were selectively important, including susceptibility to some pathogens. The clones differed from one another on average by 3.3 vegetative characters. Available online for purchase.

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  • Dirzo, Rodolfo, and John L. Harper. 1982a. Experimental studies on slug-plant interactions, III: Differences in the acceptability of individual plants of Trifolium repens to slugs and snails. Journal of Ecology 70:101–118.

    DOI: 10.2307/2259467Save Citation »Export Citation »E-mail Citation »

    Field and laboratory trials using four species of snails and slugs showed that cyanogenesis in Trifolium repens (white clover) markedly reduced, but did not completely prevent, damage to clover leaves by the grazing mollusks. A hypothetical coevolutionary interpretation of the mollusk-cyanogenesis interaction in white clover is presented.

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  • Dirzo, Rodolfo, and John L. Harper. 1982b. Experimental studies on slug-plant interactions, IV: The performance of cyanogenic and acyanogenic morphs of Trifolium repens in the field. Journal of Ecology 70:119–138.

    DOI: 10.2307/2259471Save Citation »Export Citation »E-mail Citation »

    During the growing season in a permanent pasture, pathogens damaged leaves of cyanogenic and acyanogenic morphs of Trifolium repens (white clover), but infection by the systemic rust Uromyces trifolii was almost exclusively on acyanogenic morphs. Mollusks consistently preferred acyanogenic morphs and weevils appeared not to be deterred by cyanogenesis,

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  • Harper, John L. 1969. The role of predation in vegetational diversity. In Diversity and stability in ecological systems: Report of a symposium held May 26–28, 1969. Edited by G. M. Woodwell and H. H. Smith, 48–62. Brookhaven Symposia in Biology 22. Upton, NY: Brookhaven National Laboratory.

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    Three major types of experiment are described that test the effects of herbivores on vegetation.

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  • Langlet, O. 1971. Two hundred years genecology. Taxon 20:653–722.

    DOI: 10.2307/1218596Save Citation »Export Citation »E-mail Citation »

    This paper written mostly in English, but with numerous non-English quotations, provides a detailed history of the discipline of genecology. It provides an exhaustive bibliography on differentiation in “vegetation,” including six papers from before 1800.

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  • Turkington, Roy, and John L. Harper. 1979. The growth, distribution and neighbour relationships of Trifolium repens in a permanent pasture, IV: Fine-scale biotic differentiation. Journal of Ecology 67:245–254.

    DOI: 10.2307/2259348Save Citation »Export Citation »E-mail Citation »

    This was the first paper to demonstrate that a plant population could differentiate in response to the identity of its neighbors, that is, the biotic environment, independent of the abiotic factors of the environment. The paper was listed as “one of the top 100 most influential papers published by the British Ecological Society (1913–2012).”

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Individuals in a Population and the Plant’s-Eye-View

An underlying theme of Harper 1967 (cited under Background Development: University College of North Wales (UCNW), Bangor and Evolutionary Ecology) and of Harper 1977 (cited under Population Biology of Plants) Population Biology of Plants is that the theory of evolution by natural selection is an ecological theory. Harper stresses that the biology of a species growing in isolation may not account for its ecology. As an individual plant comes into proximity with other individuals of the same and of different species, typically marked changes take place in the behavior of that individual (Harper 1964). Harper was concerned that experiments on populations not be confused with experiments on individuals. While a Darwinian is interested in population-level processes, it is the response of the individuals within a population to the presence of their neighbors that is critical. A major disadvantage of descriptive population behavior is that it focuses on mean yield, or mean plant performance, and thereby masks the existence of plant-to-plant variation; yet, it is this variation between individuals that is the driving force of natural selection (Harper 1964). This individual-level focus is highlighted in Ross and Harper 1972; Mack and Harper 1977; and Mithen, et al. 1984. If we are to see evolutionary processes in action in plant communities we must draw our attention away from anthropomorphic scales of square meters and, instead, focus on the scale appropriate to the organism we are studying—this is asking for a plant’s-eye-view of the community, as illustrated in Harper 1977 and Turkington and Harper 1979.

  • Harper, John L. 1964. The individual in the population. Journal of Animal Ecology 33:149–158.

    DOI: 10.2307/2436Save Citation »Export Citation »E-mail Citation »

    This paper deals with individuals, the differences between them, and how between plant variation is so critical when plants come into proximity with their neighbors. Available online for purchase.

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  • Harper, John L. 1977. The contributions of terrestrial plant studies to the development of the theory of ecology. In Changing scenes in natural sciences, 1776–1976. Edited by Clyde E. Goulden, 139–157. Special Publication 12. Philadelphia: Academy of Natural Sciences.

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    The idea of viewing vegetation from a “plant’s-eye-view” is introduced.

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  • Mack, Richard N., and John L. Harper. 1977. Interference in dune annuals: Spatial pattern and neighbourhood effects. Journal of Ecology 65:345–363.

    DOI: 10.2307/2259487Save Citation »Export Citation »E-mail Citation »

    This paper explores the dynamics of interference in five sand dune annuals in a greenhouse experiment using a range of different mixtures; 13,000 individual plants were mapped.

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  • Mithen, Richard, John L. Harper, and Jacob Weiner. 1984. Growth and mortality of individual plants as a function of available area. Oecologia 62:57–60.

    DOI: 10.1007/BF00377373Save Citation »Export Citation »E-mail Citation »

    The “bare area” around a focal plant is a good predictor of plant weight. As plants grow, the relationship changes between plant weight and “bare area” available. Plants in small polygons are much more likely to die than those in larger areas.

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  • Ross, Max A., and John L. Harper. 1972. Occupation of biological space during seedling establishment. Journal of Ecology 60:77–88.

    DOI: 10.2307/2258041Save Citation »Export Citation »E-mail Citation »

    The growth rate of an individual developing seedling is largely accounted for by the distance to the nearest neighbors and its stage of growth.

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  • Turkington, Roy, and John L. Harper. 1979. The growth distribution and neighbour relationships of Trifolium repens in a permanent pasture, I: Ordination pattern and contact. Journal of Ecology 67:201–218.

    DOI: 10.2307/2259345Save Citation »Export Citation »E-mail Citation »

    If the species themselves are the prime determinants of each other’s distribution, it is of interest to ask how the species themselves sample the vegetation. A plant’s-eye-view of the community was recorded, using a method in which the plant themselves are the sampling points.

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Experimental Ecology

Prior to Harper’s studies, plant ecology had been dominated by the description of vegetation and the analysis of the biology of individual species. The Darwinian approach focusing on individuals and the hazards they experience had a brief appearance on the ecological scene in the 1920s. Three leading ecologists—Clements in the United States, Sukatschev in Russia, and Tansley in England—all carried out simple competition experiments using deliberately sown plant populations (Harper 1983), and then they promptly dropped this pursuit and returned to descriptive vegetation studies. Harper writes: “it is natural that the first stages in the growth of any science (physical or biological) should consist of the description and ordering of the material for study. The next stage is to search for correlations between and causation of what has been described” (Harper 1982, p. 12). Harper’s experimental approach was evident from his time as a first-year graduate student tutor to undergraduates in the Department of Agriculture, Oxford, in 1947 at age twenty-two years. Harper writes: “We were terribly short of standard laboratory equipment that would have been used in conventional practical classes. We even had no class microscopes. Most of my laboratory experiments were absurdly simple and involved no more equipment than a packet of seeds and some pots of soil. A student could design experiments to answer simple questions such as: Does the depth at which seeds are sown affect the time at which seedlings emerge? Does it depend on the species? Does compacting the soil have an effect? When seedlings of, for example, radish emerge from the soil do they grow more slowly if one of their two seedling leaves is removed? If half of each of the two seedling leaves is removed is the effect the same as removing one whole leaf from the pair?” He continues “A good class experiment ought to teach the elements of how science works and should be written up in a way that examines what the results mean and what they don’t. Experiments of this sort provide quantitative data for logical experimental design, primitive statistical analysis and also for argument about repeatability. If two students do the same experiment at the same time will they get exactly the same result? If one student repeats the same experiment at different times will it give exactly the same results? (It usually doesn’t). How wary should one be in drawing conclusions. I had certainly never been taught science in this way either at university or at school” (J. L. Harper, unpublished memoirs; provided by Claire, his daughter). Monitoring of populations and of individuals often produces valuable information but it is ecologically not very useful unless the monitoring is coupled with experiments to understand the mechanisms underlying observed changes. Yet, despite the emphasis on experimental ecology, Harper also recognized the value and necessity of detailed descriptive observations as a prelude to experimental testing. The field at Henfaes was often used in such a way, as detailed, for example, in Cahn and Harper 1976, Turkington and Harper 1979, and Dirzo and Harper 1982.

  • Cahn, Martin G., and John L. Harper. 1976. The biology of leaf mark polymorphism in Trifolium repens L., I: Distribution of phenotypes at a local scale. Heredity 37:309–325.

    DOI: 10.1038/hdy.1976.95Save Citation »Export Citation »E-mail Citation »

    Detailed records of the distribution of clones of Trifolium repens showed an average of three to four different clones per 10x10cm. Also, detailed maps of the distribution of white leaf morphs in 1m2 quadrats.

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  • Dirzo, Rodolfo, and John L. Harper. 1982. Experimental studies on slug-plant interactions, IV: The performance of cyanogenic and acyanogenic morphs of Trifolium repens in the field. Journal of Ecology 70:119–138.

    DOI: 10.2307/2259868Save Citation »Export Citation »E-mail Citation »

    A contour map showing the density of active slugs in the field.

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  • Harper J. L. 1982. After description. In The plant community as a working mechanism. Edited by Edward I. Newman, 11–25. Special Publication of the British Ecological Society 1. Oxford: Blackwell.

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    Perhaps more so here than in any other paper, Harper discusses (vents his frustration) what he perceives to be some of the dangers in the thinking and writing of ecologists.

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  • Harper, John L. 1983. A Darwinian plant ecology. In Evolution from molecules to men. Edited by D. Bendall, 323–345. Cambridge, UK: Cambridge Univ. Press.

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    An overview and analysis of the intensive research done by graduate students (Cahn, Dirzo, Lovett Doust, Peters, Sarukhan, Thorhallsdottir, Trathan, Turkington) and a visiting researcher (Burdon), in a single small (1 ha) field of permanent grassland at the College Farm at Henfaes, Aber, near Bangor in North Wales.

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  • Turkington, Roy, and John L. Harper. 1979. The growth distribution and neighbour relationships of Trifolium repens in a permanent pasture, I: Ordination pattern and contact. Journal of Ecology 67:201–218.

    DOI: 10.2307/2259345Save Citation »Export Citation »E-mail Citation »

    A general description of the field at Henfaes, including topography, soils, and distributions of individual species.

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Ecological Theory

Harper 1977a and Harper 1980 contend that plant ecology was directionless and had little in common intellectually with animal ecology because it lacked a comparable theoretical base. Using Dobzhansky’s statement: “Nothing in biology has meaning except in the light of evolution” as a springboard (Dobzhansky 1973), Harper reasoned that if Dobzhansky were correct, and if evolution is about individuals and their descendants, that is, fitness, we should not expect to reach any real ecological understanding from studies that focus at levels higher than the individual, whether they deal with descriptive ecology, production ecology, or the gross population phenomena of the population biologist. When we study a population, community, or ecosystem, we are studying the product of those individuals that left descendants. This is the link between demography and selection, and therefore between ecology and evolution, and ultimately these are the links that give plant ecology a sound theoretical basis. The application of demographic theory to plants has been hindered because of confusion over the definition of an individual. Clonal growth in which the product of a zygote grows to become a series of rooted shoots, which sometimes sever, creates a difficulty. Evolution depends on some zygotes leaving more descendant zygotes than others. Most plants grow by the addition of repeated modules of structure (typically a shoot, root, and an axillary bud). Therefore, a demographic theory of plants needs to recognize two levels of population organization: the genetic individual and the modular unit of structure (Harper 1977b, Harper 1980, Harper and White 1974).

  • Dobzhansky, T. 1973. Nothing in biology has meaning except in the light of evolution. American Biology Teacher (March): 125–129.

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    The case is made that only the theory of evolution can account for the diversity of life, the unity of life, and, indeed, everything biological that we observe on the earth.

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  • Harper, John L. 1977a. The contributions of terrestrial plant studies to the development of the theory of ecology. In Changing scenes in natural sciences, 1776–1976. Edited by Clyde E. Goulden, 139–157. Special Publication 12. Philadelphia: Academy of Natural Sciences.

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    The three types of investigation that have dominated plant ecology are evaluated: descriptive, production, and population ecology. The paper highlights some of the outstanding questions in the three areas and the problems that evolutionary thinking poses to ecological interpretation.

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  • Harper, John L. 1977b. Plant relations in pastures. In Plant relations in pastures. Edited by J. R. Wilson, 3–14. Melbourne: Commonwealth Scientific and Industrial Organization.

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    Much emphasis is laid on understanding the behavior of individuals so that we may be able to interpret what we know about the behavior of populations. This has been done at both the immediate (proximate) ecological level and at the longer-term (ultimate) evolutionary level.

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  • Harper, John L. 1980. Plant demography and ecological theory. Oikos 35:244–253.

    DOI: 10.2307/3544432Save Citation »Export Citation »E-mail Citation »

    Examples are given to illustrate the theory that a plant is a population of parts that are born and die and the ways in which such a theory can be applied to field studies.

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  • Harper, John L., and James White. 1974. The demography of plants. Annual Review of Ecology and Systematics 5:419–463.

    DOI: 10.1146/annurev.es.05.110174.002223Save Citation »Export Citation »E-mail Citation »

    This review examines some of the theoretical bases for the development of plant demography (birth and death statistics) and surveys the current knowledge of the topic.

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Plant Population Dynamics

Population dynamics deals with the way populations are affected by birth, death, immigration, and emigration rates, that is, the vital rates of a population over time, and it has a broad overlap with demography. Ultimately, such analyses of birth and death statistics must focus attention on the need to discover the mechanisms that control, limit, or regulate population size. A few earlier studies had been conducted by Tamm in Sweden, Rabotnov in Russia, Sagar in England, and Antonovics in Wales, but it was John Harper and his students who brought the subject to prominence. This effort began with a four-part series on “Studies in the dynamics of plant populations” (e.g., Cavers and Harper 1967; Putwain and Harper 1972), a paper (White and Harper 1970), and review (Harper and White 1971).

  • Cavers, Paul B., and John L. Harper. 1967. Studies in the dynamics of plant populations, I: The fate of seed and transplants introduced into various habitats. Journal of Ecology 55:59–71.

    DOI: 10.2307/2257716Save Citation »Export Citation »E-mail Citation »

    This was the first study in the Harper lab to conduct a within- and between-species comparison of seed germination and seedling establishment. The study demonstrates that seeds of the weedy Rumex obtusifolius and R. crispus, and a maritime ecotype of R. crispus, were able to germinate in a variety of habitats but that the selection sieve was much stronger at the seedling than at the germination stage. The study also showed that the greatest disparity among the three biotypes was that the two weedy biotypes performed differently from the maritime biotype.

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  • Harper, John L., and James White. 1971. The dynamics of plant populations. In Proceedings of the Advanced Study Institute on Dynamics of Numbers in Populations, Oosterbeek, the Netherlands, September 1970. Edited by J. den Boer and G. R. Gradwell, 41–63. Wageningen, The Netherlands: Centre for Agricultural Publishing and Documentation.

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    A schematic model is presented that describes the behavior of plant populations at the successive stages (called sieves or filters) that regulate plant populations: seed bank, environmental factors, growth crowding and interference, seed production.

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  • Putwain, Philip D., and John L. Harper. 1972. Studies in the dynamics of plant populations, V: Mechanisms governing sex ratio in Rumex acetosa and R. acetosella. Journal of Ecology 60:113–129.

    DOI: 10.2307/2258045Save Citation »Export Citation »E-mail Citation »

    Demonstrates that frequency-dependent control of biased sex ratios in two species was more effective at high density and argues that the sexes of each species show such frequency-dependent interaction because they occupy at least partly different ecological niches.

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  • White, James, and John L. Harper. 1970. Correlated changes in plant size and number in plant populations. Journal of Ecology 58:467–485.

    DOI: 10.2307/2258284Save Citation »Export Citation »E-mail Citation »

    This research confirms the 3/2 power law that relates the number of surviving plants in a population undergoing self-thinning to their mean dry weight and extends the law to several other species.

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Germination

Once seeds are dispersed their continued survival depends upon landing on a substrate suitable for germination. Many seeds will be eaten and others will land on surfaces not suitable for germination and may be induced or enforced into a dormant state (Harper 1957). The soil surface may then be considered to operate as a filter or sieve determining which seeds germinate to produce seedlings (Harper and White 1971, cited under Plant Population Dynamics). The idea of the soil surface acting as a sieve has been shown in some detail by a series of experiments began in the 1950s by Harper and his associates (Harper, et al. 1955) on the influence of the environment on seed and seedling mortality (see, e.g., Sagar and Harper 1960; Harper, et al. 1965; Williams and Harper 1965; Cavers and Harper 1966). These studies demonstrated that slight variations in the soil surface impose a rigorous filter on sites in which a seed can, or cannot, germinate. In addition, there are species-specific subtleties in the requirements for germination and seed size and shape that play a major role influencing the probability of germination (Harper, et al. 1970).

  • Cavers, Paul B., and John L. Harper. 1966. Germination polymorphism in Rumex crispus and Rumex obtusifolius. Journal of Ecology 54:367–382.

    DOI: 10.2307/2257955Save Citation »Export Citation »E-mail Citation »

    Differences in germination response were observed between seeds of the same species but from different habitats, different plants (of the same species) in the same habitat, and different positions on the same plant. The survival value of germination polymorphism is discussed.

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  • Harper, John L. 1957. The ecological significance of dormancy and its importance in weed control. In Proceedings of the IVth International Congress of Crop Protection, Hamburg 1990. Edited by Johannes Krause, 415–420. Brunswick, Germany: International Congress of Crop Protection.

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    Seed dormancy maintains a reserve of seeds that are not exposed to hazards faced by the growing plant and a population of genotypes permitting an overlap of generations and a buffering of a population against temporary selective forces.

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  • Harper, John L., Phyllis A. Landragin, and Jerzy W. Ludwig. 1955. The influence of environment on seed and seedling mortality, I: The influence of time of planting on the germination of maize. New Phytologist 54:107–118.

    DOI: 10.1111/j.1469-8137.1955.tb06165.xSave Citation »Export Citation »E-mail Citation »

    This is the first of a series of eight papers showing how micro-scale heterogeneity of the soil surface acts as a filter or sieve allowing some seeds to germinate but preventing others from doing so.

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  • Harper, John L., Peter H. Lovell, and Keith G. Moore. 1970. The shapes and sizes of seeds. Annual Review of Ecology and Systematics 1:327–356.

    DOI: 10.1146/annurev.es.01.110170.001551Save Citation »Export Citation »E-mail Citation »

    A classic with more than 1,000 citations, in this review the authors argue that seed sizes and shapes are both complex adaptive compromises; seed size is a compromise with seed number, and seed shapes are compromises between the forms most efficient for dispersal, landing, and seedling establishment.

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  • Harper, John L., and James White. 1971. The dynamics of plant populations. In Proceedings of the Advanced Study Institute on Dynamics of Numbers in Populations, Oosterbeek, the Netherlands, September 1970. Edited by J. den Boer and G. R. Gradwell, 41–63. Wageningen, The Netherlands: Centre for Agricultural Publishing and Documentation.

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    The sieves or filters that regulate plant populations operate at all stages in the plant life cycle; the most risky stages, that is, when the filters are most rigorous, are during germination and establishment.

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  • Harper, John L., J. Trevor Williams, and Geoff R. Sagar. 1965. The behaviour of seeds in soil, I: The heterogeneity of soil surfaces and its role in determining the establishment of plants from seed. Journal of Ecology 53:273–286.

    DOI: 10.2307/2257975Save Citation »Export Citation »E-mail Citation »

    The so-called graveyard experiment. One key message is the danger of drawing conclusions from a single study. Harper particularly liked this experiment because it was used by “at least 20 ecology classes in universities throughout the world because it was so easy to do—but I often received letters telling me that someone’s particular class obtained a different result than what we published. Of course! That was one of the main points of the study” (personal communication).

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  • Sagar, Geoff R., and John L. Harper. 1960. Factors affecting the germination and early establishment of plantains (Plantago lanceolata, P. media and P. major). In The biology of weeds. By Geoff R. Sagar and John L. Harper, 236–245. British Ecological Society Symposium 1. Oxford: Blackwell.

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    When seeds and seedlings of the three species were sown in various habitats, the phases of germination and early seedling life were critical for the establishment of a species. Only rarely was it possible either to introduce a species into a habitat or to increase its density by sowing seeds

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  • Williams, J. Trevor, and John L. Harper. 1965. Seed polymorphism and germination, I: The influence of nitrates and low temperatures on the germination of Chenopodium album. Weed Research 5:141–150.

    DOI: 10.1111/j.1365-3180.1965.tb00337.xSave Citation »Export Citation »E-mail Citation »

    Chenopodium album is polymorphic for seed shape and color and four categories can be recognized. All four types may be borne by one plant and they differ in germination requirements.

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Regulation

Population regulation is a fundamental process related to most phenomena in ecology and underlies most other topics of interest, such as interference (competition) and the structure and dynamics of populations and communities. In natural plant populations numbers are kept within certain bounds by density-dependent forces. When population density is high, the population (of individuals or of ramets) will likely decrease, whereas increases tend to occur when population densities are low. Harper first discussed plant population regulation in the Biology of Weeds (Harper 1960, cited under The Biology of Weeds) Symposium to the British Ecological Society, and then in more detail in “The regulation of numbers and mass in plant populations” (Harper 1968, also cited under Background Development: University College of North Wales (UCNW), Bangor). Regulation is also a central issue in the highly cited papers of Kays and Harper 1974 and Watkinson and Harper 1978.

  • Harper, John L. 1968. The regulation of numbers and mass in plant populations. In Population biology and evolution. Edited by Richard C. Lewontin, 139–158. New York: Syracuse Univ. Press.

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    The main theme of this paper is that animal population theory cannot always be applied to plant populations because plants have suspended animation (dormancy), have enormous individual plasticity (because of their modular structure and clonal growth), and are strongly influenced by neighbors because they can’t run away like animals can.

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  • Kays, Stanley, and John L. Harper. 1974. The regulation of plant and tiller density in a grass sward. Journal of Ecology 62:97–105.

    DOI: 10.2307/2258882Save Citation »Export Citation »E-mail Citation »

    Yield per unit area rapidly becomes independent of the number of plants present and is dominated by the availability of resources. Over a period of twenty weeks populations converged toward a tiller density and a mean tiller weight that was independent of the thirtyfold range in seed densities.

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  • Watkinson, Andrew R., and John L. Harper. 1978. The demography of a sand dune annual: Vulpia fasciculate, I: Natural regulation of populations. Journal of Ecology 66:15–33.

    DOI: 10.2307/2259178Save Citation »Export Citation »E-mail Citation »

    Based on data collected from frequent monitoring and a manipulative field experiment, this paper presents a model that describes the population dynamics of a sand dune annual in terms of the density-dependent regulation of spikelet number and the density-independent mortality of individuals.

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Competition

Harper and his colleagues were perplexed by the diversity of natural vegetation and why so many species could coexist, often closely related species especially in light of both Gause’s competitive exclusion principle and because Darwin argued that the severest competition should come from the most similar species. Competition among plants was foremost in Harper’s thinking and he contended that chapter 3 of The Origin of Species (“The Struggle for Existence”) was the best writing ever on competition. In Harper’s presentation at the symposium of the Society for Experimental Biology (Harper 1961), he lists seven major problems in biology that require information on the manner and effects of interference (competition) between organisms for their solution, and in his presentation to the Eleventh International Congress of Genetics he describes in detail the nature and consequences of interference among plants (Harper 1964). This theme, a struggle between neighbors for limiting resources, is prominent in Harper 1967 (cited under Background Development: University College of North Wales (UCNW), Bangor and Evolutionary Ecology), Presidential address to the British Ecological Society and six of the twenty-four chapters of Harper 1977 (cited under Population Biology of Plants) are devoted to the effects of the proximity of neighbors. It is no surprise that much of the research from Harper’s lab dealt with competition, the most highly cited being Harper and Chancellor 1959; Sagar and Harper 1961; Clatworthy and Harper 1962; Obeid, et al. 1967; Mack and Harper 1977; and Schmid and Harper 1985.

  • Clatworthy, John N., and John L. Harper. 1962. The comparative biology of closely related species living in the same area, V: Inter- and intraspecific interference within cultures of Lemna spp. and Salvinia natans. Journal of Experimental Botany 13:307–324.

    DOI: 10.1093/jxb/13.2.307Save Citation »Export Citation »E-mail Citation »

    Three species of floating pondweed (Lemna) and a floating fern (Salvinia) were grown in pure culture and in mixtures at high and low densities. The success of a species in mixture could not be predicted from the parameters of growth in pure culture.

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  • Harper, John L. 1961. Approaches to the study of plant competition. In Mechanisms in biological competition. Edited by the Society for Experimental Biology, 1–39. Symposia of the Society for Experimental Biology 15. New York: Academic Press.

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    Due to the confusion about the meaning of the word “competition,” Harper proposed replacing it with “interference” to be used “as a blanket word to describe those hardships which are caused by the proximity of neighbours (usually other organisms feeding at the same trophic level)” (p. 1).

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  • Harper, John L. 1964. The nature and consequence of interference amongst plants. In Genetics today: Proceedings of the XIth International Congress of Genetics, The Hague, the Netherlands, September 1963. Vol. 2. Edited by S. J. Geerts, 465–482. Oxford: Pergamon.

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    This paper focuses attention on the reaction of a plant to its neighbors as a critical, often the most critical, part of the autecology of a species and to suggest that this type of study has a unifying function in the science of plant ecology.

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  • Harper, John L., and A. Patricia Chancellor. 1959. The comparative biology of closely related species living in the same area, IV: Rumex: Interference between individuals in populations of one and two species. Journal of Ecology 47:679–695.

    DOI: 10.2307/2257298Save Citation »Export Citation »E-mail Citation »

    Pot experiments were made to determine the nature of the interference between plants of five species of Rumex under controlled conditions of sowing density, species mixtures, water regime, and soil type. There were strong responses to water regime and soil type and four of the species showed the same general pattern of response.

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  • Mack, Richard N., and John L. Harper. 1977. Interference in dune annuals: Spatial pattern and neighbourhood effects. Journal of Ecology 65:345–363.

    DOI: 10.2307/2259487Save Citation »Export Citation »E-mail Citation »

    This was one of the first studies to show that the outcome of interference was influenced by the identity and size of a plant’s neighbors and how those neighbors were arranged around the focal plants. The paper was listed as “one of the top 100 most influential papers published by the British Ecological Society (1913–2012)”.

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  • Obeid, Mohammed, David Machin, and John L. Harper. 1967. Influence of density on plant to plant variation in fiber flax Linum usitatissimum L. Crop Science 7:471–473.

    DOI: 10.2135/cropsci1967.0011183X000700050019xSave Citation »Export Citation »E-mail Citation »

    In this study, plants developed a log normal frequency distribution of dry weight with age and increased density. Other plant traits, such as capsule number per plant and mean seed number per capsule and individual seed weight, develop different frequency distributions. This emphasizes how plant-to-plant variation itself changes with density.

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  • Sagar, Geoff R., and John L. Harper. 1961. Controlled interference with natural populations of Plantago lanceolata, P. major and P. minor. Weed Research 1:163–176.

    DOI: 10.1111/j.1365-3180.1961.tb00017.xSave Citation »Export Citation »E-mail Citation »

    The results of this experiment suggest that grasses play an important role in determining the presence or absence of particular Plantago species and also in controlling the size of the existing plantain populations.

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  • Schmid, Bernhard, and John L. Harper. 1985. Clonal growth in grassland perennials, I: Density and pattern-dependent competition between plants with different growth forms. Journal of Ecology 73:793–808.

    DOI: 10.2307/2260147Save Citation »Export Citation »E-mail Citation »

    Clones of a phalanx (Bellis) and guerrilla (Prunella) growth form were used to investigate competition between and within clones and between species. Differences in response were caused by the differences in growth form of the two species.

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Reproductive Strategies

Although Harper had written about the reproductive biology of British poppies in 1966, it was not until the Darwinian approach (Harper 1967, cited under Background Development: University College of North Wales (UCNW), Bangor and Evolutionary Ecology) that he explored the topic in detail. He presents the reader with seven research questions. The way in which an organism allocates its resources may have profound ecological consequences. For example, any plant should allocate resources to leaving offspring (seed output and ramet production) (Harper, et al. 1970), to competitive ability (height growth, leaves, stems, roots etc.), and to predator avoidance (unpalatable structures, such as defensive chemicals or spines). Harper was particularly interested in the strategy of reproduction and when he was writing in 1967 this branch of plant ecology was virtually unstudied. This subject is studied in Ogden and Harper 1970 and Bazzaz, et al. 1979.

  • Bazzaz, Fakhri A., Roger W. Carlson, and John L. Harper. 1979. Contribution to reproductive effort by photosynthesis of flowers and fruits. Nature 279:554–555.

    DOI: 10.1038/279554a0Save Citation »Export Citation »E-mail Citation »

    The authors challenge some of the assumptions made in studies of reproductive allocation and particularly the conventional estimation of reproductive effort. The paper reports an analysis of the carbon budget of reproduction for fifteen temperate deciduous trees.

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  • Harper, John L., Peter H. Lovell, and Keith G. Moore. 1970. The shapes and sizes of seeds. Annual Review of Ecology and Systematics 1:327–356.

    DOI: 10.1146/annurev.es.01.110170.001551Save Citation »Export Citation »E-mail Citation »

    Table 1 in this paper summarizes the proportion of net annual assimilation that is involved in reproductive effort. It includes grain crops and herbaceous perennial and annual plants. Table 2 shows the ranges in seed weight (up to ten orders of magnitude).

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  • Ogden, John, and John L. Harper. 1970. The reproductive strategy of higher plants, I: The concept of strategy with special reference to Senecio vulgaris L. Journal of Ecology 58:681–698.

    DOI: 10.2307/2258529Save Citation »Export Citation »E-mail Citation »

    This paper describes the partitioning of dry matter and energy throughout the life cycle of different plant species and considers the concepts of energy allocation, strategy and tactics, and the measurement of “reproductive effort,” primarily in relation to annual composites.

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Demography

Demography describes and attempts to explain numbers and changes in numbers of organisms—population flux, age distribution, age at death, survivorship, life expectancy—and it has much in common with population dynamics. Harper and White 1974 (cited under Ecological Theory) and Harper 1978 argue that if plant ecology were to be brought within the hard predictive sciences, we could not avoid paying much greater attention to demographic analysis. Demographic study of the type envisioned by Harper and White focuses attention on the life span of individuals and on the time and cause of death. Such data can be obtained only by detailed observations of individual plants that are marked for repeated observations, such as in studies that include Sarukhán and Harper 1973 on three species of Ranunculus; Watkinson and Harper 1978 on Vulpia fasciculata; Noble, et al. 1979 on Carex arenaria; and Lovett Doust 1981 on Ranunculus repens.

  • Harper, John L. 1978. The demography of plants with clonal growth. In Structure and functioning of plant populations. Edited by A. H. J. Freysen and J. W. Woldendorp, 27–48. Amsterdam: North-Holland.

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    Evolution happens because some individuals, with certain genotypes, leave more descendants than others. However, higher plants express the genotype in repeated modular units within an individual, and they express their response to environmental stress mainly by altering the number of modular units.

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  • Lovett Doust, Lesley. 1981. Population dynamics and local specialization in a clonal perennial (Ranunculus repens), I: The dynamics of ramets in contrasting habitats. Journal of Ecology 69:743–755.

    DOI: 10.2307/2259633Save Citation »Export Citation »E-mail Citation »

    The demography of ramets was monitored in two adjacent populations of the clonal perennial Ranunculus repens in park grassland and in mixed deciduous woodland. The terms phalanx and guerrilla are introduced to describe the different patterns of clonal growth. There are two other papers in this series: II: “The Dynamics of Leaves, and a Reciprocal Transplant-Replant Experiment,” Journal of Ecology 69 (1981): 757–768; and III: “Responses to Light and Nutrient Supply,” Journal of Ecology 75 (1987): 555–568.

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  • Noble, James C., Adrian D. Bell, and John L. Harper. 1979. The population biology of plants with clonal growth, I: Morphology and structural demography of Carex arenaria. Journal of Ecology 67:983–1008.

    DOI: 10.2307/2259224Save Citation »Export Citation »E-mail Citation »

    This manipulative field study monitored the structural demography of a rhizomatous species in two dune systems. Plots were established in the mature, senile, and slack phases of natural populations; half the plots received a massive nutrient application of NPK fertilizer. The shoot populations within permanent quadrats were mapped at frequent intervals.

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  • Sarukhán, José, and John L. Harper. 1973. Studies on plant demography: Ranunculus repens L., R. bulbosus L. and R. acris L., I: Population flux and survivorship. Journal of Ecology 61:675–716.

    DOI: 10.2307/2258643Save Citation »Export Citation »E-mail Citation »

    Arguably the most detailed plant demographic study ever undertaken. A census of all plants, including seedlings, of three species of Ranunculus (more than 9,000 individuals) was taken at intervals of a few weeks over 2.5 years in a grazed pasture. The three species had quite different life cycles, that is, solutions to survival in this one pasture. This paper was listed as “one of the top 100 most influential papers published by the British Ecological Society (1913–2012).”

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  • Watkinson, Andrew R., and John L. Harper. 1978. The demography of a sand dune annual: Vulpia fasciculate, I: The natural regulation of populations. Journal of Ecology 66:15–33.

    DOI: 10.2307/2259178Save Citation »Export Citation »E-mail Citation »

    Permanent quadrats were mapped regularly on two sand dune systems to obtain data on the fates of seedlings and the reproductive performance of each individual plant. Natural densities of the plants were also manipulated to assess the role of density in regulating the populations.

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Demographic Approach to Plant Form (Plasticity)

Some of the earliest studies on plant demography say less about the number of individuals in a population than about the number of units or modules within a single plant. The number of units determines the size of the plant, and their arrangement determines plant form. Plants are extremely variable in size and growth form (plasticity), and this feature along with clonal growth (vegetative reproduction) has seriously hindered the development of plant demography. Many plants grow by producing rooted branches, for example, strawberry, white clover (Trifolium repens), some buttercups (Ranunculus), bracken fern (Pteridium aquilinum), and trembling aspen (Populus tremuloides). The demographer has to decide on how to define an individual, which could be either the genetic individual, that is, everything that grew from a single seed, or the unit of structure that forms a shoot aboveground. The definition of these two interlinked problems made possible a rigorous development of plant population biology, in general, and of demography and population dynamics, in particular (Harper and Bell 1979, Harper 1981). In essence, the genetic individual may be considered as a population of parts (Bazzaz and Harper 1977, White 1979) in which the parts themselves have birth and death statistics separate from the birth and deaths of genetic individuals in the population. Harper and White 1974 and Harper 1981 contend that an understanding of the demography of the parts is the starting point for some aspects of the demography of separate individuals and Harper 1978 (cited under Demography) and Sackville, et al. 1987 have drawn particular attention to plants with clonal growth. Viewed in this way, growth in such an organism is itself a demographic process (Harper 1980, cited under Ecological Theory). Any effective theory of plant demography must take into account the two levels at which birth and death occurs: the birth and death of genetic individuals and the birth and death of the modules or units that make up the genetic individual. Maillette 1982 applies the idea to the population of buds in silver birch.

  • Bazzaz, F. A., and John L. Harper. 1977. Demographic analysis of growth of Linum usitatissimum. New Phytologist 78:193–208.

    DOI: 10.1111/j.1469-8137.1977.tb01558.xSave Citation »Export Citation »E-mail Citation »

    This study shows that the application of life-table and other demographic analyses to leaf birth and death is feasible and permits an interpretation of plant response to environmental factors at a more sophisticated level than is possible from classical growth analysis.

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  • Harper, John L. 1981. The concept of population in modular organisms. In Theoretical ecology. 2d ed. Edited by Robert M. May, 53–77. Oxford: Blackwell.

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    This is probably Harper’s most exhaustive treatment of the modular construction of plants, clonal growth, and plasticity, and why any theory of plant population dynamics must take into account both the dynamics of individual genotypes (genets) and the dynamics of modules (ramets) within a genotype.

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  • Harper, John L., and Adrian D. Bell. 1979. The population dynamics of growth form in organisms with modular construction. In Populations dynamics: The 20th symposium of the British Ecological Society, London 1978. Edited by R. M. Anderson, D. Turner, and L. R. Taylor, 29–52. Oxford: Blackwell.

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    Plants are not different from animals; rather, organisms with modular growth (mostly plants but also some animals such as Obelia, corals, Hydra) are different from those with unitary construction (mostly animals). The paper also makes the case that “form” is a result of demographic processes.

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  • Harper, John L., and James White. 1974. The demography of plants. Annual Review of Ecology and Systematics 5:419–463.

    DOI: 10.1146/annurev.es.05.110174.002223Save Citation »Export Citation »E-mail Citation »

    Presents the view that any general theory of plant demography that fails to consider both levels of demography, the genetic individual (the genet) and the modules that make up that individual genet, is seriously incomplete. A recognition of this dualism allows the plant demographer to deal with clonal growth and plasticity.

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  • Maillette, Lucie. 1982. Structural dynamics of silver birch, I: The fates of buds. Journal of Applied Ecology 19:203–218.

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    This study considers the crown of a tree as a population of repeated units (buds, leaves, shoots, flowers) with demographic properties. The author analyzes the structural dynamics of the growth of silver birch (Betula pendula) using demographic techniques. The second paper in this series is: “II: A Matrix Model of the Bud Population,” Journal of Applied Ecology 19 (1982): 219–223.

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  • Sackville, Hamilton, N. Ruaraidh, Bernhard Schmid, and John L. Harper. 1987. Life-history concepts and the population biology of clonal organisms. Proceedings of the Royal Society of London, Biological Sciences 232:35–57.

    DOI: 10.1098/rspb.1987.0060Save Citation »Export Citation »E-mail Citation »

    A model is presented of a size-structured population of genetic individuals (genets), in which each genet consists of an age-structured metapopulation of modules. The predicted responses to r- and K-selection differ markedly from those predicted for unitary organisms: r-selection may favor clonal growth with no reproduction, whereas K-selection favors greater reproduction.

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  • White, James. 1979. The plant as a metapopulation. Annual Review of Ecology and Systematics 10:109–145.

    DOI: 10.1146/annurev.es.10.110179.000545Save Citation »Export Citation »E-mail Citation »

    Retains the word population for a collection of genetically distinct individuals and proposes metapopulation for the collection of genetically identical modules within a plant. This review collates a diffuse literature on the plant as a metapopulation. Historical aspects are treated first followed by a review of modern studies. Available online for purchase.

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Books

John Harper published one major textbook, Population Biology of Plants (Harper 1977), co-authored two very successful undergraduate textbooks, and edited or coedited three volumes that feature multiple authors.

Population Biology of Plants

Population Biology of Plants, Harper’s 892-page tome, has been affectionately known as “The gospel according to John.” Throughout this book, Harper emphasizes the importance of Darwinian natural selection and the necessity of accurate census data and experiments to address questions at both the population and community levels of organization. Most chapters pose numerous questions, many of which remain to be answered. At least nine different ecological journals reviewed the book and to a large extent they were glowingly positive (Woodell 1977, Mooney 1978, van der Meijden 1978), but some reviews pointed out weak coverage of certain topics (van der Meijden) especially physiology and genetics (Solbrig 1979). Although published in 1977 it is still a rich source of information and ideas. Harper noted with irritation that the book (which as of February 2015 has more than 11,000 citations) was often cited carelessly by many researchers merely to support poorly formed ideas. Throughout the volume, Harper points out ways in which plant and animal populations are similar and different. In the preface to the 2010 edition, printed thirty-one years after the original publication, Sarukhán, Dirzo, and Franco write that Harper’s book “linked the conceptual and theoretical developments in population ecology, mostly derived from the study of animals, with field observations and experimental evidence of population regulation and life history evolution in plants. The field of population biology was already well established in the 1960s although with a clear zoocentric emphasis, however, it is because of Harper’s work that the field experienced a veritable explosion, reached maturity and became a mainstream scientific endeavour worldwide. This field is so vast now that it would be pointless, if not impossible, for someone to summarise it. It is precisely because of this that PBP [Population Biology of Plants] is as relevant now as it was in 1977. John Harper’s style of highlighting unanswered questions and the limitations of both theory and empirical evidence served and still serves as foundation for research agendas worldwide. Much remains to be done in this field and this alone makes PBP an essential element in the library of every student/researcher of population biology, whether interested in plants or animals.”

Ecology: From Individuals to Ecosystems and Essentials of Ecology

It is unusual for an undergraduate textbook to have more than 1,200 citations in the primary ecological literature. Such is the quality of both of these textbooks, written in collaboration with Michael Begon (Liverpool) and Colin Townsend (Otago, New Zealand). The first volume was published in 1986, is now in its fourth edition (Begon, et al. 2006), and has served as the standard undergraduate ecology textbook for more than twenty years. The book separates itself from other textbooks, in typical Harperian fashion, by recognition that ecology is a constantly evolving subject with its own uncertainties and controversies; thus, readers are forced to think about and evaluate alternative ideas rather than providing “the answer.” In reviewing the book, Robert Smith (Nature 319 [1986]: 809) writes: “The freshness of approach and breadth and depth of coverage make most of the opposition [undergraduate ecology textbooks] seem rather stale and restricted diet by comparison. . . and all teachers of ecology should sample this nouvelle cuisine.” Both of these textbooks have had a profound influence on a generation of undergraduates and various editions have been translated into many languages, including German, Spanish, Russian, Japanese, and, more recently, Chinese, Korean, and Portuguese. In 2007 the authors received a Lifetime Achievement Award from the British Ecological Society.

  • Begon, Michael, Colin R. Townsend, and John L. Harper. 2006. Ecology: From individuals to ecosystems. 4th ed. Oxford: Blackwell.

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    This undergraduate textbook has served as the standard advanced textbook in ecology for nearly twenty years. It is comprehensive in coverage, exploring ecological concepts with relevant field and laboratory studies. Formerly known as Ecology: Individuals, Populations and Communities. Originally published in 1986.

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  • Townsend, Colin R., John L. Harper, and Michael Begon. 2008. Essentials of ecology. 3d ed. Oxford: Blackwell.

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    This textbook along with its larger companion text of Begon, et al. 2006 served as forerunners in the science of ecology to a generation of undergraduate students. Originally published in 1999.

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The Biology of Weeds

John Harper’s upbringing on a farm and agricultural background are clearly reflected in the subjects used in much of his research—crop plants, grasses, and weeds. During the 1950s Harper and his colleagues began a series of studies on the influence of the environment on seed and seedling mortality and, from 1953 to 1960, they gave increasing attention to the study of weeds. The natural development from these early studies ultimately led to the holding of the first symposium of the British Ecological Society, which was titled The Biology of Weeds; he was editor of the book (Harper 1960) that stemmed from this conference.

  • Harper, John L., ed. 1960. The biology of weeds. Symposium of the British Ecological Society 1. Oxford: Blackwell.

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    This book includes the proceedings of the first symposium held by the British Ecological Society. It consists of twenty-four chapters (papers) on all aspects of weed biology, including history, ecology, taxonomy, germination, dormancy, dispersal, and competition written by many of the most notable weed biologists at that time.

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Other Books

Harper was also coeditor of two other volumes with multiple authors: Chaloner, et al. 1991 and Silvertown, et al. 1997.

  • Chaloner, William G., John L. Harper, and John H. Lawton, eds. 1991. The evolutionary interaction of animals and plants. Philosophical Transactions of the Royal Society of London, Biological Sciences 333. London: Royal Society.

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    This is a series of fourteen papers written by leading ecologists. Topics range from fossil evidence for plant-arthropod interactions, pollination, and herbivory to evolution of leaf shape, plant secondary chemical diversity, insect morphology, and cellulose digestion in insects. Each chapter is followed by a discussion, and the final chapter is “The Croonian Lecture” by Tony Bradshaw.

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  • Silvertown, Jonathan, Miguel Franco, and John L. Harper, eds. 1997. Plant life histories: Ecology, phylogeny and evolution. Cambridge, UK: Cambridge Univ. Press.

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    This book examines the phylogenetic relationship between plant life history traits and provides an important synthesis of thinking on a multifaceted problem. The final section of the book focuses on interactions between plants and competitors and herbivores and microbial symbionts, recognizing that these interactions may have an ancient evolutionary history.

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Legacy

John Harper’s legacy includes his own accomplishments and recognition in the field of plant population biology (see the section Awards and Service), his participation in service on various advisory boards, and what he sometimes called his academic progeny—he was proud of his students. His legacy also includes gems of wisdom for which he will be remembered, such as his plea for clarity and precision and his distaste for fuzzy thinking. Harper was also proud of the legacy produced by his many students. He left a profound ecological footprint, especially in Mexico, the United States, Canada, and parts of Europe (Franco, et al. 2009). Two of his former students, José Sarukhán and Rodolfo Dirzo, were elected foreign associates of the US National Academy, and Sarukhán was also elected a foreign member of the Royal Society. Lesley Clegg (now Lesley Lovett Doust) served as provost and vice president for academic affairs at Michigan Technical University in Houghton, Michigan, until 2009, before being appointed president and vice chancellor of Nipissing University in North Bay, Ontario, where she served from 2009 to 2012. For a number of years, José Sarukhán was president of the largest university in the world (UNAM) in Mexico City. Many of John Harper’s students became major influences in their own right (see the section Biography). Twenty-eight former collaborators representing eight nationalities from nine countries contributed to Harper’s festschrift (White 1985) on the occasion of his sixtieth birthday. Individuals representing more than twenty nationalities participated as members of Harper’s lab either as students or as visitors, and eighteen of his former students hold faculty positions in universities around the world.

Collaborations and Mentorship

Harper’s career is noteworthy for his legacy as a mentor. Harper published many single-authored papers and typically coauthored (although not always) at least one paper with each of his students and visitors. A review of Harper’s publications demonstrates the enormous mentoring he brought to generations of students, doctoral graduates, and visitors. Many students left Harper’s lab to become major influences in their own right. To mark Harper’s sixtieth birthday, James White coordinated production of a festschrift that includes twenty-four chapters written by twenty-eight former collaborators representing eight nationalities from nine countries (White 1985). Individuals representing more than twenty nationalities were members of Harper’s lab either as students or as visitors, and eighteen of his former students hold faculty positions in universities around the world. Such is the global influence of the uniquely Harperian approach to plant ecology, which, of course, is also a major aspect of his legacy.

Clarity and Precision

Harper was known for his rapier-sharp wit and equally sharp intellect. But his insistence on clarity and precision in thinking and writing constitutes perhaps his greatest intellectual trait. Harper was ruthless in combatting fuzzy thinking, and had abhorred use of sloppy terminology. In Harper 1982 (cited under Experimental Ecology), he attacks usage of the words stress, strategy, and adaptation. In Begon, et al. 2006 (cited under Ecology: From Individuals to Ecosystems and Essentials of Ecology), and in Townsend, et al. 2008 (cited under Ecology: From Individuals to Ecosystems and Essentials of Ecology), the word adaptation is dismissed in the early pages and apparently not used again. He particularly disliked the term vegetative reproduction: “if a trees spreads vertically we call it growth, but if a clover spreads laterally we call it reproduction—nonsense” (personal communication). He loathed the word competition, or at least the sloppy way in which the term had been used by ecologists, and preferred instead the more general term interference “as a blanket word to describe those hardships which are caused by the proximity of neighbors (usually other organisms feeding at the same trophic level)” (Harper 1961, p. 1, cited under Background Development: Oxford, Department of Agriculture). While the word interference appears in the titles of eight papers ranging from Harper and Chancellor 1959 (cited under Competition) to Mack and Harper 1977 (cited under Individuals in a Population and the Plant’s-Eye-View); nevertheless, the word competition creeps into the titles of three of his papers (Harper 1961, cited under Background Development: Oxford, Department of Agriculture; Schmid and Harper 1985, cited under Competition; Franco and Harper 1988). Interestingly, all of these phobia-words are used in his landmark A Darwinian Approach to Plant Ecology (Harper 1967, cited under Background Development: University College of North Wales (UCNW), Bangor and Evolutionary Ecology), although competition is used only once and it is in quotations. When challenged on his use of these words in early papers, Harper responded: “Am I not allowed to change my mind?” (question and discussion period, Royal Society Symposium, 1985).

Complete Bibliography of the Published Works of John L. Harper

These citations represent the complete works of which Harper is an author. Most of the coauthored papers that have been annotated above have been cited more than 130 times (Web of Knowledge or Google). Harper did not keep a record of papers for which he was not a coauthor, even though numerous papers were published by his students and visitors while in his lab. A few of the more significant of these publications are included as annotations throughout this “Complete Bibliography” but compilation of a complete list has not been attempted.

I. Thesis

  • Harper, John L. 1950. An investigation of the interaction of soil micro-organisms with special reference to the study of the bacterial populations of plant root systems. PhD diss., Magdalen College, University of Oxford.

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    Harper’s D.Phil. work was never published, but the ideas and work in Part V of the thesis “A study of the rhizosphere of some banana varieties” were integrated into Harper 1950a and Harper 1950b (both cited under Papers, Book Chapters, and Conference Proceedings). About his thesis, Harper wrote, “When I came to write up my D.Phil. thesis . . . . technical problems formed half the thesis. I wrote a paper to Nature about them which was accepted but I withdrew it when I discovered yet another technical problem about sampling.” (J. L. Harper, unpublished memoirs; provided by Claire, his daughter).

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II. Papers, Book Chapters, and Conference Proceedings

III. Books and Edited Volumes

IV. Reviews of Population Biology of Plants

V. Biographic and Bibliographic

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