This Week's Citation Classic

Robert H. MacArthur. Population Ecology of Some Warblers of Northeastern Coniferous Forests. Ecology, Vol. 39, No. 4. (Oct., 1958), pp. 599-619.

I really love the old-style Ecology papers; they often stretched for dozens of pages and read like books. Robert MacArthur's paper on the population ecology of some warblers of northeastern coniferous forests is no exception, and is such a contrast to the terse, jargon-loaded style often found in the pages of Nature and Science.

The paper, MacArthur's first as an assistant professor after obtaining his PhD from G. Evelyn Hutchinson at Yale University, stemmed from his dissertation, and contained a marvelous exposition of the division of ecological niches among five closely related warbler species among the coniferous forests of upstate New York. As MacArthur writes, "these species are congeneric, have roughly similar sizes and shapes, and all are mainly insectivorous. They are so similar in general ecological preference, at least during years of abundant food supply, that ecologists studying them have concluded....these species might provide an interesting exception to the general rule that species either are limited by different factors or differ in habitat or range."

That is, the warblers seemed to violate the rule of one species per niche.

However, as MacArthur's research showed, the warblers subtly divided their living space, with different species focusing on slightly different habitats as the figure at the top of the blog shows. What's more is that warbler species were regulated in a density-dependent fashion; they increased when rare, and decreased when common. There were other differences too, differences only apparent to one that carefully observes the birds day in and day out over the seasons (MacArthur was a consummate birdwatcher): "there are differences of feeding position, behavior and nesting date, which reduce competition. These, combined with slight differences in habitat preference and perhaps a tendency for territoriality to have a stronger regulating effect on the same species than upon others, permits the coexistence of the species." The net effect was that several closely related species could share a common area without directly competing over the same resources.

MacArthur was a true artist of biology; "MacArthur would say that the best science comes, to a great extent, from the creation of de novo and heuristic classification of natural phenomena. 'Art,' he enjoyed quoting Picasso, 'is the lie that helps us to see the truth.'"1

MacArthur was taken from us during his prime at 42 years of age by renal cancer. One wonders what contribution he may have made had he survived to the present.

MacArthur's impact on Ecology was so considerable that The Robert H. MacArthur Award is given biannually by the Ecological Society of America to an established ecologist in mid-career for meritorious contributions to ecology, in the expectation of continued outstanding ecological research. Talks by many recipients have been presented at the annual meeting of the society and subsequently published in Ecology.

Stephen Fretwell writes on "The Impact of Robert MacArthur on Ecology" in the Annual Review of Ecology and Systematics".

1 E.O. Wilson and E.G. Hutchinson. 1989. Robert Helmer MacArthur 1930-1972. National Academy of Sciences Biographical Memoirs 58: 319-327.