2022/10/19 by Daniel Simberloff · 1 citation
Biochemistry, Genetics and Molecular Biology · Agricultural and Biological Sciences · Environmental Science · #Insect and Arachnid Ecology and Behavior #Plant and animal studies #Ecology and Vegetation Dynamics Studies
paper · doi:10.1086/721257
openalex publication_date 2022/10/19 · openalex created_date 2022/10/20 · openalex updated_date 2026/07/14
Previous articleNext article FreeIn Memoriam Edward O. Wilson (1929–2021): It All Started with AntsDaniel SimberloffDaniel SimberloffDepartment of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 Search for more articles by this author PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreThe death of Edward O. Wilson on December 26, 2021, at the age of 92 occasioned outpourings of grief at the passing of perhaps the most prominent conservationist of our time, widespread notice in the popular media, a profusion of obituaries, and debate over his legacy. Most obituaries briefly noted his youth in Alabama and subsequent arrival at Harvard and then recounted, to a greater or lesser extent, a few of his scientific accomplishments. Many focused particularly on his contributions to the study and conservation of biodiversity, and several mentioned controversies surrounding sociobiology. Amid widespread recent recognition that science is not isolated from the societal and institutional inequities of our day and that the influence of these inequities may be unearthed in scientists' careers and activities, scientists' lives and beliefs have increasingly been probed in assessments of their scientific contributions. I have recounted several personal interactions with Wilson in a blog posted soon after his death (Simberloff 2022) that are relevant to my understanding of Wilson as a person. Here I will focus on his scientific contributions to evolution and ecology, which are the purview of this journal.The basic elements of Wilson's youth are related in both his autobiography, Naturalist (Wilson 1994), and a biography, Scientist (Rhodes 2021), published shortly before his death. The terse titles elegantly capture the salient features of his remarkable career. Both Wilson himself and his biographer, Richard Rhodes, describe his early fascination with nature—ants, of course, but also butterflies and snakes—including his fortuitous discovery at age 13 of the red imported fire ant Solenopsis invicta in a vacant lot in Mobile, Alabama. After earning a BS degree in 1949 and an MS degree in 1950 at the University of Alabama, Wilson enrolled as a doctoral student at the University of Tennessee. William Brown, Wilson's correspondent during his undergraduate days and subsequent lifelong friend, and Aaron Sharp, a botanist at the University of Tennessee, urged Wilson to apply to transfer to Harvard, and Frank Carpenter, who had advised Brown's doctorate at Harvard, facilitated Wilson's transfer and became his doctoral advisor. Wilson enrolled at Harvard in 1951 and spent the remainder of his academic career there.Most notices of Wilson's passing cite three main scientific contributions—the dynamic equilibrium theory of island biogeography (e.g., MacArthur and Wilson 1967), the promulgation of sociobiology as a scientific field (e.g., Wilson 1975), and research on and advocacy of biodiversity conservation (e.g., Wilson 1988a, 1988b). However, had he never engaged in these three efforts, Wilson would still be recognized as a prominent biologist. His fascination with the geography of life yielded two concepts that continue to stimulate research. In 1956, Brown and Wilson described the phenomenon of character displacement: the greater phenotypic difference between sympatric populations of two related species than between allopatric populations of the same species. Character displacement quickly influenced much research on a plethora of species (Dayan and Simberloff 2005), is treated by current major ecology textbooks, and continues to inspire scientists (Pfennig and Pfennig 2020). A Web of Science search found the original article cited 1,243 times (529 times during the past decade). In 1959, Wilson depicted a novel cyclical pattern of spread and speciation of ponerine ants in Melanesia (1959a). He extended this "taxon cycle" model of island ecology and evolution to several other ant groups in 1961 (Wilson 1961). Students of diverse taxa (e.g., birds, fishes, lizards, beetles, and freshwater shrimp) continue to frame their research in terms of tests of the taxon cycle model (e.g., Pepke et al. 2019), and the 1961 article has been cited 401 times (177 times during the past decade) according to a Web of Science search.Had Wilson focused solely on ants and not extended his ambit to social behavior in general, his contributions would have ensured a lasting position as a scientist of the first order. His pioneering work on ant pheromones, beginning with an alarm and digging pheromone in the harvester ant Pogonomyrmex badius (Wilson 1958) and a trail-making pheromone in the red imported fire ant S. invicta (Wilson 1959b), is part of an extensive corpus of research on behavior in several species of ants. The behavioral research, in turn, is the central element in copious research on diverse aspects of ant ecology, evolution, and systematics, much of which is summarized by Wilson in The Insect Societies (1971) and by Hölldobler and Wilson in The Ants (1990). That the latter book won a Pulitzer Prize for General Nonfiction is a remarkable accomplishment for a specialized scientific textbook.Perhaps any brief recounting of a mass of scientific study as broad as Wilson's would inevitably seem to enumerate rather distinct lines of research, but it is important to recognize the ways in which for Wilson they lead or blend into one another, often beginning with his focus on ants. For instance, Wilson himself placed the origins of the dynamic equilibrium theory at his meeting with Robert MacArthur at a 1960 American Association for the Advancement of Science meeting in New York City (Wilson 1994; Rhodes 2021), but key elements of the theory—the dynamism and islands—were of course present in his mind before this as he worked through data to arrive at his taxon cycle model. The taxon cycle entails key elements of the equilibrium theory—species arriving on and disappearing from islands. Whereas Wilson envisioned the taxon cyclic colonization and extinction of ants in Melanesia as occurring on an evolutionary timescale, the equilibrium theory conceives of island biotas as undergoing these processes in ecological time on many islands, and it also extends the theoretical domain to island-like habitats, such as lakes or forests surrounded by fields: that is, patches or islands of habitat separated from similar patches by a "sea" of other habitat types inhospitable to the "island" biota. Wilson (1994) detailed the development of this theory in frequent correspondence and occasional meetings with MacArthur, including a note from MacArthur in 1962 with a version of the crossed immigration and extinction curves now reprinted in virtually every ecology textbook. The full theory appeared the next year, with specific application to birds on Indo-Pacific islands (MacArthur and Wilson 1963). The book most frequently cited as a reference for the theory, The Theory of Island Biogeography, appeared four years later (MacArthur and Wilson 1967) and in 2001 was reprinted with the sobriquet "Princeton Landmark in Ecology." In addition to applications to islands and island-like systems beyond the Indo-Pacific, the book contains related ideas, such as an explanation based on the equilibrium theory of island biotas that are "radically mixed"—that is, that contain species that appear to derive from two distinct sources. The related idea most frequently cited is that of r- and K-selection, which MacArthur and Wilson named and derived from several older works, including one by MacArthur (Stearns 1976), and applied to island colonization.The equilibrium theory struck a responsive chord and quickly led to research ostensibly applying it to many different biotas (Simberloff 1974). The great majority of these studies, however, did not actually present data demonstrating a dynamic process; rather, they depicted a positive species-area relationship and observed, following MacArthur and Wilson, that such a relationship is predicted by the theory. However, because other explanations exist for a species-area relationship (e.g., a positive relationship between area and the number of habitats), an observed species-area relationship is not strong evidence for the equilibrium theory. Another quickly voiced concern was whether data used to support the existence of ongoing immigration and extinction actually represent population processes, as envisioned by the theory, or simply the movement of individuals within widely ranging populations (Lynch and Johnson 1974).The equilibrium theory spread into the rapidly developing science of modern conservation biology with several nearly simultaneous publications in 1974 and 1975, including one by Wilson himself (Wilson and Willis 1975), enunciating a series of criteria for refuge design to maximize species richness. Although these were ostensibly based on the equilibrium theory, in fact only the first criterion (a large refuge will contain more species than a smaller, otherwise identical one) derives directly from the theory; indirectly and with additional assumptions, the criterion that refuges connected by corridors are superior to unconnected refuges is also predicted by it (Simberloff 1988). Nevertheless, in short order these design criteria came to be seen as conventional wisdom, spurred by their incorporation in 1980 into the World Conservation Strategy of the International Union for the Conservation of Nature and Natural Resources, and they appeared in the first spate of modern conservation biology textbooks (e.g., Primack 1993).The original basic underlying theory of a dynamic equilibrium number of species remains frequently cited by community ecology researchers, although with wide recognition that it may not apply to many insular biotas (Losos and Ricklefs 2010). By 2000, Brown and Lomolino had tagged it as outmoded and foresaw an imminent paradigm shift in biogeography. Similarly, its application to refuge design faded with recognition that refuges differ from oceanic islands in many ways and that the idiosyncrasies of particular species and systems render the specific criteria ascribed to the theory questionable in many circumstances (Wu and Vankat 1995; Warren et al. 2020). Perhaps the main conservation legacy of this application of the theory is the frequent advocacy of corridors between refuges as a means of maintaining population viability (cf. Kareiva and Marvier 2017).However, as pointed out by Haila and Järvinen (1982), the real scientific value of the equilibrium theory is missed if one focuses on the extent to which islands actually do have an equilibrium number of species that is maintained by ongoing immigration and local extinction. Rather, the question is whether the theory served as a conceptual framework yielding insights into the structure and dynamics of insular (in the broad sense) communities and populations and whether it inspired further fruitful research. In this regard, surely the dynamic equilibrium theory of island biogeography qualifies as a major accomplishment. Perhaps its main direct long-term influence is focusing attention on just how persistent local populations are and, to the extent that they occasionally disappear, the reasons for their extinction.This focus, in turn, heavily contributed to the development of an extensive science of metapopulations. The relationship between metapopulation theory and the equilibrium theory was ascribed by Richard Levins, its founder, to an agreement among Levins, MacArthur, and Wilson that they would work on complementary questions, essentially how many species an island contains for MacArthur and Wilson and how many islands a species occupies for Levins (Warren et al. 2020). In the main founding article of metapopulation theory, Levins (1970) cites the frequent extinction posited by MacArthur and Wilson (1967) and the observed extinction on defaunated small mangrove islands in an early test of the equilibrium theory (Simberloff and Wilson 1969; Wilson and Simberloff 1969) as motivating his study of extinction. To some extent metapopulation theory superseded the refuge design criteria in the 1990s (Hanski and Simberloff 1997), and it remains an active area of research in conservation biology and ecology (Hanski and Gaggiotti 2004; Begon and Townsend 2021). The equilibrium theory and metapopulation theory have together spawned research on metacommunities (e.g., Leibold and Miller 2004; Leibold et al. 2004; Logue et al. 2011; Massol et al. 2011) and metaecosystems (e.g., Loreau et al. 2003; Gravel et al. 2011; Massol et al. 2011; Leibold and Chase 2017), key components in the rise of spatial ecology (Massol et al. 2011; Fletcher and Fortin 2018).Another active area of research inspired by the dynamic equilibrium theory is Stephen Hubbell's "unified neutral theory of biodiversity and biogeography" (Hubbell 1997, 2001), which arose directly from Hubbell's attempt to characterize and understand the distribution of population sizes within a community (e.g., Hubbell 1979) and to relate this distribution to the species richness of the community. The unified neutral theory has been controversial (e.g., Dornelas et al. 2006; McGill et al. 2006; Ricklefs 2006) but has served as a null model both in its original domain of ecological communities (e.g., Nee 2005; Jabot and Chave 2011; Rosindell et al. 2011, 2012) and for other sorts of biotas (e.g., Li and Ma 2016) and questions (e.g., Buschke and Sinclair 2019). To a greater or lesser degree, the dynamic equilibrium theory substantially influenced the development of a number of other lines of research on the ecology and evolution of island biotas (Warren et al. 2015).Although the concept of r- and K-selection developed by MacArthur and Wilson (1967) is only tangentially related to the core dynamic equilibrium theory (Warren et al. 2020), it remains widely cited. Reznick et al. (2002) traced its early great influence on life history research (e.g., Pianka 1970) and found it generally replaced by focus on mortality forces and patterns, but it is still fruitfully applied to studies of life history (e.g., Sæther et al. 2016) and many related questions (e.g., Bohn et al. 2014; Yin et al. 2022). It is also the basis of several racist publications that cite it directly or through its inclusion in Wilson's subsequent book, Sociobiology (discussed below). The attention the dynamic equilibrium theory drew to frequent local extinctions, combined with metapopulation theory, led to the concept of a minimum population size (Shaffer 1981, 1987), and the book by MacArthur and Wilson (1967) was the direct inspiration for demographic stochasticity as one factor contributing to local extinctions and determining a minimum viable populations size in specific settings. The concept was soon expanded to population viability analysis (Boyce 1992). Estimation of minimum viable population sizes as part of population viability analysis has become a staple in conservation research and management of imperiled populations (Traill et al. 2007; Brook et al. 2011; Chaudhary and Oli 2020).Wilson's extensive research on ant behavior was one of the inspirations for his attempted synthesis of behavior throughout the animal kingdom, Sociobiology: The New Synthesis (Wilson 1975), as he observed in the final chapter of The Insect Societies (Wilson 1971), "The Prospect for a Unified Sociobiology." However, Wilson described his interactions with his first graduate student, primatologist Stuart Altmann, as leading by 1956 to consideration of seeking "common principles to explain insect societies and primates" (Wilson 1994, p. 253), which they even termed "sociobiology." A research trip with Altmann to a rhesus colony on Cayo Santiago (Puerto Rico) was "a stunning revelation and an intellectual turning point" (Wilson 1971, p. 309). Certainly by the late 1960s, when we spent long hours in the field conducting experimental research to test the theory of island biogeography, Wilson frequently discussed his sociobiology project and mentioned various accounts he had read of social behavior by vertebrates—especially mammals and birds. A key inspiration that, in his mind, helped transform his vast catalog of individual species behaviors into the "common principles" he had been seeking was Hamilton's 1964 article on kin selection, which he read with astonishment and quickly handed to me during my first graduate year, both to confirm and to firm up his grasp of the mathematical treatment, and he expressed the view that if the article was correct, it revolutionized our understanding of the evolution and nature of the social behavior of at least the Hymenoptera and quite possibly that of many other species as well. In Sociobiology, he continued to be excited by kin selection, as modified by consideration of sex ratio (Trivers and Hare 1976), asserting that "nothing but kin selection seems to explain the statistical dominance of eusociality by the Hymenoptera" (pp. 417–418) and invoking it for certain other species as well (e.g., several jay species). His autobiography (Wilson 1994) describes how his initial skepticism about kin selection was converted to wholehearted acceptance.Wilson's volte-face regarding kin selection (Wilson 2005; Wilson and Hölldobler 2005) and suggestion that group selection was the key force driving the evolution of eusociality was therefore quite remarkable, and for several years it was occasionally but not frequently contested (e.g., Foster et al. 2006). His collaboration with mathematical biologists Martin A. Nowak and Corina E. Tarnita (Nowak et al. 2010) combining his rejection of kin selection with an alternative mathematical model elicited a plethora of objections, initiated by five immediate responses (one with 137 coauthors; Abbot et al. 2011) rejecting their contention that kin selection and the associated concept of inclusive fitness had been a distracting, erroneous detour in research on the evolution of eusociality and altruistic behavior in general. Whatever views posterity will have of the merits of the two sides of this debate, an irony is that Wilson surely had much to do with the rising influence of Hamilton's ideas of kin selection and inclusive fitness that he pilloried beginning in 2005. A Web of Science search shows that through 1971, the year Wilson published The Insect Societies, Hamilton's 1964 article was cited only 38 times. Beginning in 1972, its citation rate rapidly accelerated to nearly 100 each year by the end of the decade; through 2021 it had been cited 10,324 times, and Hamilton's ideas on kin selection and inclusive fitness remain enormously influential in evolutionary circles.As with the dynamic equilibrium theory of island biogeography, the specific hypotheses Wilson proposed in Sociobiology: The New Synthesis elicited objections and controversy (Segerstråle 2000), especially with respect to his view, explicitly presented in the final chapter, that human social behavior should be studied and interpreted in a fashion similar to that of other animals and his further development of that idea in On Nature (Wilson and his extended of the concept of r- and K-selection in Sociobiology, in several racist particularly by (e.g., and However, his lasting in this area will be the promulgation and of a science of the and study of the basis and nature of social behavior throughout the animal respect to his research spurred and influenced the development of a of research often termed the evolutionary social et al. 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