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ROBERT HELMER MACARTHUR
April 7, 1930-November 1, 1972
BY EDWARD O. WILSON AND
EVELYN G. HUTCHINSON
IN NOVEMBER ~ g7 ~ a brief but remarkable era in the
development of ecology came to a tragic, premature
close with the death of Robert MacArthur at the age of 42,"
wrote Martin Cody anct Jarec! Diamond in the 1975 memorial
volume, Ecology and Evolution of Communities.
MacArthur will be remembered as one of the founders of
evolutionary ecology. It is his distinction to have brought pop-
ulation and community ecology within the reach of genetics.
By reformulating many of the parameters of ecology, bio-
geography, anti genetics into a common framework of fun-
damental theory, MacArthur more than any other person
who worked cluring the decisive decade of the 1960s set
the stage for the unification of population biology.
MacArthur was the youngest son of John Wood Mac-
Arthur, a professor of genetics at the University of Toronto
and Marlboro College in Vermont. After completing his
unclergraduate education at the latter institution and taking
a master's clegree in mathematics at Brown University, Robert
MacArthur took a Ph.D. in 1957 at Yale University, under the
direction of G. Evelyn Hutchinson. In order to receive ad-
clitional training in field ornithology, he spent the academic
year ~ 957-l 958 with David Lack at Oxford University.
Hutchinson, Lack, and an older brother, the physicist John
319
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BIOGRAPHICAL MEMOIRS
W. MacArthur, Jr., were dominant influences in shaping
MacArthur's unique blend of mathematical and ecological in-
terests. From ~ 958 to ~ 965, MacArthur advanced from as-
sistant professor to full professor at the University of Penn-
sylvania. He then moved to Princeton University, where he
ended! his career as Henry Fairfielc! Osborn Professor of Biol-
ogy. In 1952 he marries! Elizabeth Bayles Whittemore, with
whom he had four children (Duncan, Alan, Elizabeth, and
Donald).
MacArthur began his career with three articles that re-
vealec! an unusual power and originality of approach. The
first (1955) was the proposal of a way to measure community
stability taken from information theory, formalizing for the
first time a concept that, until then, could only be expressed
through verbal description.
Soon afterward (1957) came the celebrated "broken-stick"
mocle} of the relative abundance of bird species. Although
the specific hypothesis of competition embodied in the bro-
ken-stick distribution has been ctisputed and the approach
was later dismissed as obsolete by MacArthur himself, we
should not overlook the real significance of this contribution,
which dicl indeed appear to describe what happens in nature
in some as yet imperfectly studied circumstances. In three
short pages, MacArthur audaciously confronted a central
problem of community ecology that previous writers had
scarcely formulated in words. He characterized the issue in
such a way as to suggest that the deepest remaining mysteries
of natural history can be reached by leaps of the imagina-
tion so long as such efforts are ctisciplined by the postula-
tional-cleductive method.
Reviewers sometimes forget that the broken-stick hypoth-
esis was only one of three frequency distributions presented
in the article, each derived from a clifferent, competing set
of biological hypotheses. The method of multiple working
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ROBERT HELMER MACARTHUR
321
hypotheses was thereby introduced to this branch of ecolog-
ical theory. The 1957 article set the tone for all of Mac-
Arthur's later work. Inevitably, his approach was condemned
by some ecologists as oversimplification, but—right or wrong
in particular applications it energized a generation of
young population biologists and transformed a large part of
ecology.
MacArthur's third early contribution was an elegant anal-
ysis of niche division in warblers (19581. For this somewhat
more conventional study, he received the Mercer Award of
the Ecological Society of America. The warbler stucly re-
vealecl the real secret of MacArthur's success, his almost
unique status as a mathematician-naturalist. He was a math-
ematician of professional gra(le, having been trained in the
discipline before commencing the formal study of ecology.
He shared the conviction of pure mathematician G. H.
Harcly, whom he resemblec! very much in temperament anct
philosophy, "that a mathematician was a maker of patterns
of ideas, and that beauty ant! seriousness were the criteria by
which his patterns shouIcl be judged."
In conversation, MacArthur would say that the best sci-
ence comes, to a great extent, from the creation of de novo
ant! heuristic classification of natural phenomena. "Art," he
enjoyed quoting Picasso, "is the lie that helps us to see the
truth." But MacArthur was also a born naturalist. He watcher!
.
birds with the patience and skill of a professional ornitholo-
gist, visited the tropics as often as he could, and delightecl in
the encIless facts of natural history, which were temporarily
exempted from his Cartesian scalpel. The store of random
information thus accumulated and the shadowy play of its
many patterns were the real inspiration of his theoretical
work.
The decade of the 1960s was a period of intense activity
for Robert MacArthur. While serving on the faculty of the
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BIOGRAPHICAL MEMOIRS
University of Pennsylvania and then at Princeton, he began
a parallel series of investigations, many in collaboration with
colleagues anct students, that touched on a wicle range of
topics around the central problem of species cliversity. Part
of his special genius was an ability to work closely with per-
sons of widely varying talents and interests, to turn them into
fast friends, anct to bring out the best in their scientific labors.
One of them, E. O. Wilson, who coauthored this memoir,
recorder! the following impression of him:
He was medium tall and thin, with a handsomely angular face. He met
you with a level gaze supported by an ironic smile and widening of eyes.
He spoke with a thin baritone voice in complete sentences and paragraphs,
signaling his more important utterances by tilting his face slightly upward
and swallowing. He had a calm understated manner, which in intellectuals
suggests tightly reined power. Because very few intellectuals can keep their
mouths shut long enough to be sure about anything, MacArthur's restraint
gave his conversation an edge of finality he did not intend. In fact he was
basically shy and reticent. He was not a mathematician of the first class-
very few scientists are, otherwise they would become pure mathemati-
cians but he joined superior talent in that field with an extraordinary
creative drive, decent ambition, and a love of the natural world, birds, and
science, in that order.
MacArthur and his coworkers analyzed the evolution of
the demographic parameters, established the environmental
correlates of bird (diversity, and formulated and partly solvecl
the species packing problem. One of his most influential
works, The Theory of Island Biogeography (1967), written with
Wilson, create(1 species equilibrium theory. This theory ex-
plored the many ramifications of a balance of species number
on islands and on "habitat islands," any sharply demarcated
habitat—such as a lake, or even, for insects at least, a tree in
~ E. O. Wilson, Biophilia (Cambridge, Massachusetts: Harvard University Press,
1984), p. 68. A further account of MacArthur's collaborative work and its impact on
ecology has been given by Sharon E. Kingsland in Modeling Nature: Episodes in the
History of Population Ecology (Chicago: University of Chicago Press, 1985).
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ROBERT HELMER MACARTHUR
323
the micicIle of a field. During colonization, the extinction rate
in species/unit time rises as the number of species on the
island rises ant! the immigration rate falls. When the two
converge, a dynamic equilibrium is attained in which the con-
tinuing turnover varies according to the speed with which
the colonization took place. The models predict an increase
in species numbers with larger island! area and greater prox-
imity to the mainIanct. Other investigators have addect many
refinements to this basic theory. Experimental tests have also
been performed on isolated habitats, from bottles of nutri-
ents to full-scale islancts and islanct habitats in the Florida
Keys ant} the Brazilian Amazon.
The current theory of islancl biogeography, while still very
inadequate for the largest ant! most complex systems, has
worked well enough to become an important part of both
ecology ant] biogeography. It is also a cornerstone of the new
field! of conservation biology because of its relevance to the
study of the extinction process and the planning of natural
reserves.
As time passed MacArthur spoke of himself increasingly
as a biogeographer ant! made the subject the focus of his
teaching at Princeton. In 1971, when he learner! he hac! only
a year or two left to live, he quickly brought the many threads
of his work together in the single book, Geographical Ecology:
Patterns in the Distribution of Species. The clarity and incisive-
ness of this synthesis show him at the height of his power.
Geographical Ecology is both the reflective memoir of a senior
scientist and the prospectus of a young man whose creative
effort ended at the point of its steepest trajectory.
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BIOGRAPHICAL MEMOIRS
SELECTED BIBLIOGRAPHY
1955
Fluctuations of animal populations, and a measure of community
stability. Ecology, 36:533-36.
1957
On the relative abundance of bird species. Proc. Natl. Acad. Sci.
USA, 43:293-95.
1958
With P. Klopfer. North American birds staying on board ship dur-
ing Atlantic crossing. Br. Birds, 51 :358.
A note on stationary age distributions in single species populations
and stationary species populations in a community. Ecology,
39: 146-47.
Population ecology of some warblers of northeastern coniferous
forests. Ecology, 39:599-619.
1959
With G. E. Hutchinson. A theoretical ecological model of size dis-
tributions among species of animals. Am. Nat., 93:117-25.
With G. E. Hutchinson.- On the theoretical significance of aggres-
sive neglect in interspecific competition. Am. Nat., 93:133-34.
On the breeding distribution pattern of North American migrant
birds. Auk, 76:318-25.
1960
On the relative abundance of species. Am. Nat., 94:25-36.
With P. Klopfer. Niche size and faunal diversity. Am. Nat.,94:293-
300.
On Dr. Birch's article on population ecology. Am. Nat., 94:313.
On the relation between reproductive value and optimal predation.
Proc. Natl. Acad. Sci. USA, 46:144-45.
Population studies: Animal ecology and demography. Q. Rev.
Biol., 35:82-83. Review of Cold Spring Harbor Symposium,
vol. 22.
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ROBERT HELMER MACARTHUR
325
1961
Population effects of natural selection. Am. Nat., 95: 195-99.
With P. Klopfer. On the causes of tropical species diversity: Niche
overlap. Am. Nat., 95:223-26.
With J. W. MacArthur. On bird species diversity. Ecology, 42:594-
98.
1962
With I. W. MacArthur and }. Freer. On bird species diversity. II.
Prediction of bird censuses from habitat measurements. Am.
Nat., 96:167-74.
Some generalized theorems of natural selection. Proc. Natl. Acad.
Sci. USA, 48: 1893 -97.
1963
With M. L. Rosenzweig. Graphical representation and stability con-
ditions of predator-prey interactions. Am. Nat., 97:209-23.
With E. O. Wilson. An equilibrium theory of insular zoogeography.
Evolution, 17:373 -87.
1964
Environmental factors affecting bird species diversity. Am. Nat.,
98:387-97.
With D. Garfinkel and R. Sack. Computer simulation and analysis
of simple ecological systems. Ann. N. Y. Acad. Sci., 115:943-
51.
With V. G. Dethier. A field's capacity to support a butterfly popu-
lation. Nature, 201:728-29.
With R. Levins. Competition, habitat selection, and character dis-
placement in a patchy environment. Proc. Natl. Acad. Sci. USA,
51: 1207-10.
Ecology. In: New Dictionary of Birds, ed. A. L. Thompson, pp. 230-
33. New York: McGraw-Hill.
1965
Patterns of species diversity. Biol. Rev., 40:510-33.
Ecological consequences of natural selection. In: Theoretical and
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326
BIOGRAPHICAL MEMOIRS
Mathematical Biology, ed. T. H. Waterman and H. Morowitz, pp.
388-97. New York: Blaisdell.
1966
With H. Recher and M. Cody. On the relation between habitat
selection and species diversity. Am. Nat., 100:319-32.
With R. Levins. The maintenance of genetic polymorphism in a
spatially heterogeneous environment: Variations on a theme by
Howard Levine. Am. Nat., 100:585-89.
With E. R. Pianka. On optimal use of a patchy environment. Am.
Nat., 100:603-9.
A review of The Pattern of Animal Communities by C. S. Elton. Am.
Sci., 54:497A.
With }. Vandermeer. A reformulation of alternative b of the broken
stick model of species abundance. Ecology, 47: 139-40.
Note on Mrs. Pielou's comments. Ecology, 47:1074.
With I. H. Connell. The Biology of Populations. New York: John Wiley
& Sons, Inc., Publishers.
1967
With R. Levins. The limiting similarity, convergence, and diver-
gence of coexisting species. Am. Nat., 101:37~-85.
With E. O. Wilson. The Theory of Island Biogeography. Princeton:
Princeton University Press.
1968
Selection for life tables in periodic environments. Am. Nat.,
102:381-83.
The theory of the niche. In: Population Biology and Evolution, ed.
R. C. Lewontin, pp. 159-76. Syracuse: Syracuse University
Press.
1969
Patterns of communities in the tropics. Biol. J. Linn. Soc., 1:19-
30.
The ecologist's telescope. Ecology, 50:353.
With H. S. Horn. Foliage profile by vertical measurements. Ecol-
ogy, 50:802-4.
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ROBERT HELMER MACARTHUR
327
With R. Levins. An hypothesis to explain the incidence of mono-
phagy. Ecology, 50:910-11.
Species packing and what competition minimizes. Proc. Natl. Acad.
Sci. USA, 64: 1369-71.
1970
Graphical analysis of ecological systems. In: Some Mathematical
Questions in Biology, ed. J. D. Cowan, pp. 61-73. Providence,
R.I.: American Mathematical Society.
Species packing and competitive equilibrium for many species.
Theor. Popul. Biol., 1: 1 - 11.
1971
Patterns of terrestrial bird communities. In: Avian Biology, ed. D. S.
Earner and J. R. King, vol. 1, pp. 189-221. New York: Aca-
demic Press.
1972
With J. M. Diamond and I. R. Karr. Density compensation in island
faunas. Ecology, 53:330-42.
With H. S. Horn. Competition among fugitive species in a Harle-
quin environment. Ecology, 53:749-52.
With D. MacArthur. Efficiency and preference at a bird feeder. I.
Ariz. Acad. Sci., 7:3-5.
With R. M. May. Niche overlap as a function of environmental var-
iability. Proc. Natl. Acad. Sci. USA, 69:1109-13.
Strong, or weak, interactions. Trans. Conn. Acad. Arts Sci.,
44: 177-88.
Coexistence of species. In: Challenging Biological Problems, ed. I.
Behnke, pp. 253-59. New York: Oxford University Press.
Geographical Ecology. New York: Harper & Row.
1973
With l. MacArthur, D. MacArthur, and A. MacArthur. The effect
of island area on population densities. Ecology, 54:657-58.
1974
With A. T. MacArthur. On the use of mist nets for population stud-
ies of birds. Proc. Natl. Acad. Sci. USA, 71:3230-33.
Representative terms from entire chapter:
robert helmer
