Forbes, Stephen Alfred

(b. Silver Creek, Stephenson County, Illinois, 29 May 1844; d. Urbana, Illinois, 13 March 1930)

biology.

The fifth of the six children of Isaac Forbes and Agnes Van Hoesen, Stephen A. Forbes was raised on a farm in relative poverty. When Stephen was ten, Isaac Forbes died and the elder son, Henry, supported the family. After a year at Beloit Academy, Stephen accompanied Henry into the cavalry on the Union side in the Civil War. Forbes later regarded these years of military service, from September 1861 to November 1865, including four months as a prisoner of war, as a valuable stimulus to his education.

After three years of studying medicine, Forbes decided to study natural history. He supported himself by teaching school in various Illinois towns between 1868 and 1872. Attending the Illinois State Normal University only briefly, Forbes pursued the study of natural history on his own. He married Clara Shaw Gaston in 1873 and had five children. The family was Unitarian, Forbes having moved from the orthodox religion of his childhood to a scientific agnosticism. Throughout his life Forbes was physically and mentally energetic and healthy, enjoying variety in exercise and in reading.

In 1872 he was made curator of the Museum of the State Natural History Society, Normal, Illinois, which he transformed into the Illinois State Laboratory of Natural History in 1877. The laboratory and museum were moved to Urbana when he became a professor at the University of Illinois. This was in 1884, the same year he received his Ph.D. from the University of Indiana. Forbes was appointed state entomologist in 1882. The Office of the Entomologist and the State Laboratory of Natural History were combined when the State Natural History Survey was created. Forbes was chief of the Survey until his death. Forbes’s earliest love had been botany, but his first professional concern was how best to teach natural history in the public schools. He was active in the campaign, led by Louis Agassiz, for laboratory and field work. Forbes’s first major research was a series of studies of the stomach contents of birds and fish that he collected in Illinois. Naturalists had, of course, made scattered notes of what a particular animal was observed to eat, but Forbes undertook a systematic program to determine directly, often by microscopic examination, what foods had been eaten and in what proportion. He became an authority not only on birds and fish but on the insects and crustacea that they ate. Throughout his career he maintained an interest in limnology, establishing a floating laboratory in the Illinois River in 1894. After his appointment as state entomologist in 1882, most of Forbes’s work concerned insects harmful to agriculture. Highly respected in this field, he was president of the American Association of Economic Entomologists in 1893 and 1908, president of the Entomological Society of America in 1912, and elected to the National Academy of Sciences in 1918.

The scientific work of Stephen Alfred Forbes was dominated by his interest in ecology. From the outset he was concerned to investigate scientifically, and quantitatively where possible, the interrelations that make a group of individuals into a functioning system. His viewpoint was clearly and explicitly based upon that of Charles Darwin and Herbert Spencer. He studied the food of fish and birds because he saw the predator-prey relation as the most direct ecological link between species. He expected such studies to help explain not only the geographical distribution and abundance of a species but also its evolution. Forbes found in these studies considerably less specialization than expected, although there were characteristic differences in the proportion of various foodstuffs consumed by each species. The fact that each prey species had many enemies revealed the complexity of the system. Forbes decided that the oscillations in number inherent in a simple predatorprey relation, well described by Spencer (Principles of Biology, II, 399), would be damped when these relations were more complex, and he interpreted lack of specialization as an evolutionary adaptation to avoid harmful oscillations. Forbes also found that structural factors were correlated with feeding habits only in a very general sense. The physical adaptation of predator and prey seemed less exact than Darwinists assumed, while the invisible “psychological” factor of food preference, presumed heritable, responded to natural selection.

Spencer had described the stable balance generally found in nature as the result of a physiological law governing reproductive energies, for he thought natural selection unable to produce the necessary mutual adjustment of reproductive rates. But Forbes suggested that natural selection could act on the predatorprey pair as a unit, requiring them to achieve a profitable adjustment to each other or both lose out in the struggle for existence. These apparent enemies have, he said, a common interest. Forbes believed that in the isolated and constant environment of certain lakes, the assemblage of species was “sensible,” that is, the entire system was sensitive to whatever affects one species; the assemblage is like an organism composed of interdependent organs. In the microcosm of a lake, the entire complex of species had a “community of interest,” so that natural selection would tend to produce maximum productivity and stability of the whole.

Forbes repeated these ideas from his 1880 articles, in a somewhat popularized form, in a lecture read to the Scientific Association of Peoria, Illinois, on 25 February 1887. This lecture, “The Lake as a Microcosm,” was later hailed as a minor classic by ecologists for its early statement of the concept of community. Karl Moebius’ 1877 booklet on oysters (published in English in 1883) has been similarly hailed. The idea Moebius embodied in his definition of biocoenosis was that an area would hold a given sum of life, so that should the number of oysters be reduced, the number of mussels or other species would increase to maintain the sum.

In 1907 Forbes reviewed his data of thirty years of collecting fish, with the idea of analyzing statistically the geographic distribution of different species. The probability of cooccurrence of two species was predicted from their independent frequencies in his collection; comparing this with their actual cooccurrence yielded his so-called coefficient of association. He applied a similar analysis to data collected in a special survey of birds, giving mathematical expressions for the preference of different species for different types of fields. He had wondered in 1878 whether closely related species living together ever completed for the same food; in 1884 he had described how species of insects feeding on the strawberry plant avoid direct competition by separation in time; in 1907 he hoped to use his coefficient of association to uncover “evasions of competition, and the escape from its consequences, by those closely related and similarly endowed...” (“On the Local Distribution of Certain Illinois Fishes,” in Bulletin of the Illinois State Laboratory of Natural History, 7 [1907], 275). Modern ecologists likewise find the competitive exclusion principle a fruitful basis for research.

While his understanding of the “sensibility” of an assemblage led him to warn of unwanted results if farmers and fishermen tried to alter the balance of nature with inadequate knowledge, his view of the flexibility of natural systems made him hopeful that man could learn how to alter the balance in his favor without disaster. For example, beginning in 1882 Forbes studied the natural diseases of insect pests in the hope of controlling them biologically rather than chemically. He interpreted the agricultural problems with which he dealt as state entomologist as a lack of adjustment of plant and insect, characteristic of the first, primitive stage of association, when evolulution had not yet produced mutual adaptation.

In 1859 Darwin had plainly shown not only the possibility of explicitly analyzing the dependencies of organisms but indeed that such an analysis, along with the laws of variation and inheritance, was the key to the origin of species. Yet the existing momentum of academic biology made comparative anatomy, embryology, and paleontology the fields for evolutionary studies, while ecology, like genetics, became well established only in this century. To the modern ecologist Forbes therefore seems remarkably ahead of his time, for he worked on questions not widely appreciated until twenty or thirty years later. What is perhaps more remarkable is that the science of ecology, whose problems and methods had been so clearly defined in the 1880’s, had such a long gestation period.

BIBLIOGRAPHY

I. Original Works. Most of Forbes’s work appeared in the various publications of the Office of the Illinois State Entomologist, the Illinois State Laboratory of Natural History, the Agricultural Experiment Station of the University of Illinois, and the Illinois State Natural History Survey. An extensive bibliography of his scientific articles, compiled by H. C. Oesterling, is given in Biographical Memoirs. National Academy of Sciences, 15 (1934), 26–54.

I have referred particularly to the following: “The Food of Birds,” in Transactions of the Illinois State Horticultural Society, 10 (1877), 37–44; “The Food of Illinois Fishes,” in Bulletin of the Illinois State Laboratory of Natural History, 1 , no. 2 (1878), 71–89; “Studies of the Food of Birds, Insects, and Fishes, Made at the Illinois State Laboratory of Natural History, at Normal, Illinois,” the subtitle given to no. 3 (1880) and no. 6 (1883) of the same journal.

Among his articles on insects affecting the strawberry is “On the Life-histories and Immature Stages of Three Eumolpini,” in Psyche, 4 (1884), 123–140. “The Lake as a Microcosm” was published in the first and only volume of the Bulletin of the Scientific Association of Peoria, Illinois, pp. 77–87, and reprinted in Bulletin of the Illinois State Natural History Survey, 15 (1925), 537–550. “Preliminary Report Upon the Invertebrate Animals Inhabiting Lakes Geneva and Mendota, Wisconsin, With an Account of the Fish Epidemic in Lake Mendota in 1884,” is Bulletin of the United States Fish Commission, 8 (1890), 473–487.

See also “Summer Opening of the Biological Experiment Station of the University of Illinois,” a pamphlet published by the University of Illinois (1896), 24 pp.; “On the Local Distribution of Certain Illinois Fishes: An Essay in Statistical Ecology,” in Bulletin of the Illinois Laboratory of Natural History, 7 (1907), 273–303; “An Ornithological Cross-section of Illinois in Autumn,” ibid., 305–335; and “History of the Former State Natural History Societies of Illinois,” in Science, 26 (1907), 892–898.

The third Report on the Natural History Survey of the State of Illinois (1909) is a monograph by S. A. Forbes and R. E. Richardson entitled The Fishes of Illinois; the 2nd ed. of this book was published in 1920.

Of additional interest are “Aspects of Progress in Economic Entomology,” in Journal of Economic Entomology, 2 (1909), 25–35; “The General Entomological Ecology of the Indian Corn Plant,” in American Naturalist, 43 (1909), 286–301; and “The Ecological Foundations of Applied Entomology,” in Annals of the Entomological Society of America, 8 (1915), 1–19.

A posthumously published autobiographical note, written in 1923, is “Stephen Alfred Forbes,” in Scientific Monthly, 30 (1930), 475–476.

II. Secondary Literature. The fullest account of Forbes is Leland Ossian Howard, in Biographical Memoirs. National Academy of Sciences, 15 (1934), 3–54. This incorporates material from the autobiography cited above, from a memorial pamphlet published by the University of Illinois in 1930, and from an obituary by Henry Baldwin Ward, “Stephen Alfred Forbes—A Tribute,” in Science, n.s. 71 (1930), 378–381.

Mary P. Winsor