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IAMES R. GRIESEMER • 232

Over the last century there have been three major shirts in the meaning of "niche": (1) from the nineteenth-century focus on a species' place in the balance of nature to concepts of the specific place or role of a population or species in an environment or community, (2) from the concept of place or role to a formal, geometric definition of the occupant of a place in terms of idealized environmental dimensions, and (3) from the formal definition to an operationalized description in terms of actual resource utilization (Schoener, 1989). In addition, uses of the niche concept have shifted as interests of animal ecologists changed from the geographical basis of spe-ciation and evolution to problems in community structure, to the ecolog-ical dynamics of laboratory populations, and to the evolutionary dynamics of communities. More recently, some biologists have argued for a return to some of the earliest conceptions of the niche (James et al., 1984). Others have questioned some of the perceived consequences of early conceptions of the niche, particularly the heavy emphasis on the role of competition in structuring niches (Simberloff, 1982, 1984) as well as the concept of a vacant niche (Herbold and Moyle, 1986; Colwell on NICHE).

Roswell Johnson (1910) is probably the first biologist to use the word "niche" to mean the place of an organism in nature (Gaffney, 1975; cf. Cox, 1980, and Schoener, 1989). Joseph Grinnell, however, was the first to develop a full account of the niche concept and to incorporate it into a broad program of biological research. Grinnell and Charles Elton intro-duced the niche concept independently to designate a place or role in an environment or community (Grinnell and Swarth, 1913; Grinnell, 1914, 1917a, 1924,1928, excerpts reprinted in 1943; Elton, 1924,1927,1946). Grinnell's focus on environment and Elton's on community reflect their differing theoretical programs.

Their ideas about niches- extended Darwin's metaphor of a world so filled with species that the improvement of one by natural selection often implied the "wedging" out of another (see Egerton, 1977). Grinnell's focus on problems of distribution and evolution led him to think of the niche as a unit whose limits are set by factors of food supply, shelter (including refugia from enemies and safe breeding places), competition, parasitism, temperature, humidity, rainfall, insolation, nature of the soil, and others (Grinnell, 1917b, 1928). Elton's focus on food relations as the fundamen-tal structure underlying all animal communities led him to think of niches

related concept of continuum. This list is far from comprehensive and the literature cited is far from agreement on many issues. Claims made for the first ecological use of the term "niche," for example, range from 1910 (Cox, 1980; Gaffney, 1975) to 1924 (Vandermeer, 1972). Schoener (1989) compares a variety of historical meanings of the term in relation to its role in understanding competition and an assessment of the modern niche theory and its problems. His paper complements the focus on Grinnell and Elton presented here.

NICHE: HISTORICAL PERSPECTIVES • 233

in terms of roles in food chains, such as herbivore and carnivore, although he was aware of many factors influencing these roles.

Grinnell: Geography, evolution, and the niche. Joseph Grinnell was interested in how the evolution of the environment brings populations of animals into changing association with other plant and animal species and thus drives organic evolution and speciarion (Grinnell, 1924). He used "ecologic niche" and "environmental niche" as equivalent terms (Grinnell, 1924, p. 227).

Grinnell's approach to natural history was based on late nineteenth-century traditions of biogeography, systematics, and Darwinian evolution (Mayr, 1973; Star and Griesemer, 1989; Griesemer, 1990). In considering the physical and biotic environment of a species, he developed an ecologic hierarchy of world realms, regions, life zones, fauna! areas, (plant) asso-ciations, and niches to parallel the systematic hierarchy from kingdoms to subspecies (see Grinnell, 1928). Each level of the hierarchy picked out rel-evant environmental factors that might serve as causes of speciation through effects on the distribution and abundance of species and subspe-cies. Abiotic factors were mostly associated with higher levels, for exam-ple, temperature with life zones and humidity with faunal areas. At the lowest level niches were associated with a complex of biotic and abiotic factors and were unique; each species occupied one niche, that is, one set of hierarchically characterized abiotic factors plus plant and animal spe-cies that served a variety of roles as elements of each species' environment. It is Grinnell's hierarchical concept of environmental determinants of dis-tribution that led him to characterize the niche as the ultimate distribu-tional unit (Grinnell, 1928).

Grinnell's most cited paper on the concept of niche is "The Niche-Relationships of the California Thrasher" (Grinnell, 1917a), although he first used the term "niche" in his 1913 Ph.D. dissertation (see Grinnell, 1914). (The 1917 paper is the first of Grinnell's in which "niche" appears in the title, probably explaining why some authors claim 1917 as the year of Grinnell's introduction of the term—e.g., Udvardy, 1959.) It seems probable that the term emerged from discussions among the active group of faculty and students at Stanford University attracted by the evolutionist David Starr Jordan and inspired by the western biogeographic work of C. Hart Merriam, whose life-zone concept provided a starting point for much of Grinnell's work.

The term "niche" first appears in Grinnell's published work in a paper coauthored with Harry Swarth, whose later work at the California Academy of Science on speciation in Galapagos finches predates Lack's (Grinnell and Swarth, 1913; see Cox, 1980, and Kingsland, 1985). Grinnell and Swarth characterized the niche as a subdivision of association: "As with zones and faunas, associations are often capable of subdivision; in

IAMES R. GRIESEMER • 234

fact such splitting may be carried logically to the point where but one species occupies each its own niche" (1913, p. 218).

Grinnell's idea of the niche as an ultimate distributional unit flows from his conception of "competitive exclusion," usually attributed to G. F. Gause (e.g., Hutchinson, 1957, calls it the Volterra-Gause principle; Udvardy, 1959, and Hutchinson, 1965, acknowledge Grinnell). Darwin had articulated the core idea in On the Origin of Species and Grinnell presented a similar view: "It is only by adaptations to different sorts of food, or modes of food getting, that more than one species can occupy the same locality. Two species of approximately the same food habits are not likely to remain long evenly balanced in numbers in the same region. One will crowd out the other; the one longest exposed to local conditions, and hence best fitted, though ever so slightly, will survive, to the exclusion of any less favored would-be invader" (1904, pp. 375-377).

Elton: Food chains, animal communities, and the niche. Charles Elton's widely read book, Animal Ecology, introduced a generation of scientists to a modern conception of animal community (Kingsland, 1985). The core of Elton's theoretical outlook was that ecology is the study of what organ-isms are doing in their environments. By studying the circumstances and limiting factors under which animals do what they do, Elton thought it would be possible to discern "the reasons for the distribution and numbers of different animals in nature" (Elton, 1927, p. 34).

Elton's focus on the overriding importance of food relations led him to characterize the niche primarily in terms of populations' functional roles in a community as eaters and eaten: "Animals have all manner of external factors acting upon them—chemical, physical, and biotic—and the 'niche' of an animal means its place in the biotic environment, its relations to food and enemies. The ecologist should cultivate the habit of looking at animals from this point of view as well as from the ordinary standpoints of appear-ance, names, affinities, and past history. When an ecologist says 'there goes a badger' he should include in his thoughts some definite idea of the ani-mal's place in the community to which it belongs, just as if he had said 'there goes the vicar'" (1927, pp. 63-64).

Elton's interest in functional roles stemmed from his concern to develop a coherent account of food chains and cycles and to explain his new con-cept of the "pyramid of numbers," which relates the relative sizes and num-bers of organisms to their position in a food chain (1927, chap. 5). As such, he was less interested in species per se than in comparisons among local community structures that would support generalizations about food chains, size, and relative abundance. Nevertheless, Elton was aware of a wide variety of factors influencing niches, and he often mentioned micro-habitat factors such as suitable soil types for nesting birds and places in which different species feed.

NICHE: HISTORICAL PERSPECTIVES 235

Despite the fact that Elton and Grinnell both considered biotic and abiotic factors, many textbooks distinguish the two by calling Grinnell's concept the "habitat" niche and Elton's the "functional" niche, as if to suggest that Grinnell's concept was primarily abiotic and Elton's biotic (Krebs, 1978; Ricklefs, 1979; cf. Schoener, 1989, for a counterargument). Whittaker et al. (1973, p. 322), following Dice (1952) and Clarke (1954), attempt to distinguish "place" and "functional" concepts of niche, arguing that the functional concept is the more fundamental and that part of the confusion of the two stems from the mixture of habitat and niche dimen-sions of Grinnell's (and Hutchinson's) views (see also Pianka, 1974, pp. 185—187). Grinnell's and Elton's niche concepts are better distinguished against the backdrop of their differing theoretical aims of explaining spe-ciation versus community structure, however, rather than focusing on a few aspects of their explicit definitions of "niche" (see also COMMUNITY).

Grinnell and Elton both identified the niche as the place/role a species happens to occupy in an environment, not a property of the occupying species as in the Hutchinsonian and modern resource utilization concep-tions of the niche. Grinnell wrote, "if a new ecologic niche arises, or if a niche is vacated, nature hastens to supply an occupant, from whatever material may be available. Nature abhors a vacuum in the animate world as well as in the inanimate world" (1924, p. 227).

The principal point on which Grinnell and Elton appear to differ is whether more than one species can occupy a single niche, but this stems from Elton's less precise characterization of the niche; a comparison of their examples shows the two concepts to be rather similar (Schoener, 1989). Grinnell concluded that niches are unique because his taxonomical approach took all important environmental factors into account. Elton identified functional food relations in a community loosely enough to sug-gest that niches "are only smaller subdivisions of the old conceptions of carnivore, herbivore, insectivore, etc., and that we are only attempting to give more accurate and detailed definitions of the food habits of animals" (1927, p. 64). As functional roles, niches could be filled by distinct (but often closely related) species in different communities. Elton suggested a concept of ecological "equivalents," arguing, for example, that an arctic niche filled by foxes that eat guillemot eggs and remains of seals left by polar bears is filled in tropical Africa by hyenas that eat ostrich eggs and remains of zebras killed by lions (1927, p. 65).

However, just as Elton recognized that factors other than food were often important in determining the species in a community, Grinnell fully recognized the functional nature of niches in his version of ecological equivalents, calling attention to "the great number of similar ecologic types of animals which are developed in widely separated regions and which are derived from unrelated stocks. The Kangaroo Rat of our deserts

IAMES R. GRIESEMER • 236

corresponds ecologically to the Jerboa of the Sahara; but it is derived from squirrel ancestry, while the Jerboa is more nearly related to house mice" (Grinnell, 1924, p. 227). Grinnell's conclusion that the niches of distinct species could be ecologically similar, but not identical, probably followed from his greater attention to the vast number of determining environmen-tal factors.

Grinnell tended to focus on the distribution of species into niches because he was an evolutionary biologist whose first concerns were spe-ciation and the relationship between the evolution of the environment and organic evolution (Grinnell, 1924; cf. Griesemer, 1989). Populations of the same species may be distributed among a number of local communities of the sort that interested Elton. Grinnell placed great emphasis on sub-species because these are of greatest interest to evolutionists. Elton's inter-est in evolution appears to have had more to do with population numbers and the possible role of ecologists in solving the problem of how nonadap-tive traits might spread. Elton suggested that release from competition after a population crash might allow nonadaptive traits to spread before they are scrutinized by selection (1927, chap. 12).

Early empirical studies of the niche. Empirical studies of competition in the laboratory and the field were essential to development of the niche concept (Hutchinson, 1978; Kingsland, 1985; Mcintosh, 1985). G. F. Gause (1934) brought together Elton's concept of the niche and V. Volterra's mathematical descriptions of two-species interactions in predator-prey systems to found an important branch of the experimental investigation of competition. Gause's approach was to construct simple laboratory systems based on Volterra's equations in order to see whether the predicted oscillations of predators and prey could be realized. A related but different approach was pioneered by Thomas Park in experimental studies of competition among species of the flour beetle genus Tribolium (e.g., Park, 1948, 1954b; for reviews, see Neyman et al., 1956, and Park, 1962; see Park, 1939, for a contrast between Gause's and Park's approach).

Experimental studies of competition had two important consequences for the concept of the niche. First, they focused attention squarely on cen-tral theoretical problems such as the dynamics of competition and held out hope for an ecological theory based on general principles. Second, they reinvigorated the competitive exclusion principle, which stated that "com-plete competitors cannot coexist" (Hardin, 1960, p. 1292). Complete competitors are usually understood to be species that have identical eco-logical niches. Prior to the experimental studies, competitive exclusion was perceived to be a qualitative principle so obvious as to seem uninteresting (Hutchinson, 1975; Kingsland, 1985). Also, Grinnell's earlier use of com-petitive exclusion in an integrated evolutionary view had virtually disap-

NICHE: HISTORICAL PERSPECTIVES • 237

peared as geneticists took over the development of evolutionary theory and systematists developed the new speciation theory. Gause's and Park's experiments showed that the concept of niche, in the guise of determinants of relations of competitive exclusion, was central to an understanding of population dynamics and the evolutionary structuring of communities.

Some disagreement over the utility of the niche concept stems from apparent circularity of the competitive exclusion principle. If species are observed to coexist, then by the competitive exclusion principle they must have different niches to avoid competition, whether these differences are discernible or not. If species do not coexist, then they must overlap in their niches and competition prevents, or would prevent, coexistence. Such explanations appear to be "competitionist story-telling" after the fashion of adaptationist story-telling: assume that competition is ubiquitous and you will find that you can explain all community relations in terms of competition. G. E. Hutchinson (1957, p. 418) tried to rescue the compet-itive exclusion principle by reformulating it as an empirical claim: realized niches do not intersect.

There are still dangers of circular reasoning about niches based on stud-ies of resource utilization, however: if species coexist and one resource dimension indicates too much overlap to permit coexistence, perhaps two resource dimensions will separate them; if two will not do, try three (see also RESOURCE). The competitive exclusion principle, and with it the niche concept, is thus reduced to trivaliry on the presumption that no two species will be identical in all respects, and therefore some resource dimension will explain coexistence (Hardin's "axiom of inequality"). In addition to con-ceptual problems, many naturalists were skeptical of the relevance of "bot-tle experiments" to natural populations (see, e.g., discussion by Mayr in Park, 1939, p. 254), which could only be established by attention to the problem of explaining coexistence among species in natural communities.

David Lack (1947a; see also Kingsland, 1985} studied Galapagos finch species that seemed to share niches, prompting him to give a nonadaptive explanation but then to change his interpretation in light of fine discrimi-nations in resource utilization based on bill size. Stephen Jay Gould (1983} identifies this shift as part of a broader "hardening" of the evolutionary synthesis between the 1940s and 1960s against nonadaptive explanations.

Hutchinson and his student Robert MacArthur also raised questions about how the evolution of niches permits coexistence. Hutchinson's famous "paradox of the plankton" concerned the partitioning of an appar-ently homogeneous environment so as to permit coexistence of similar plank tonic species (Hutchinson, 1961). His concept of limiting similarity expressed the limits of niche overlap that permit coexistence in measurable terms (Hutchinson, 1959; Abrams, 1983). MacArthur made an equally famous study of warblers that showed that careful field observation may

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Copyright © 1992 by the President and Fellows of Harvard College All rights reserved

Printed in the United States of America Second printing, 1994

First Harvard University Press paperback edition, 1994

Library of Congress Cataloging-in-Publication Data Keywords in evolutionary biology /

edited by Evelyn Fox Keller and Elisabeth A. Lloyd. p. cm.

Includes bibliographical references and index. ISBN 0-674-50312-0 (cloth) ISBN 0-674-50313-9 (pbk.)

1. Evolution (Biology)—Terminology. I. Keller, Evelyn Fox, 1936- . II. Lloyd, Elisabeth Anne.

QH360.6.K49 1992 575'.0014—dc20 92-8283

CIP

Designed by Gwen Frank feldt

Co NTENTS

Acknowledgments ix

Contributors xi

Introduction Evelyn Fox Keller and Elisabeth A. Lloyd

ADAPTATION: Historical Perspectives Richard M. Burian

ADAPTATION: Current Usages Mary Jane West-Eberhard

A LT R UIS M: Theoretical Contexts Alexander Rosenberg

A LT R UIS M: Contemporary Debates David Sloan Wilson and Lee A. Dugatkin

ALTRUISM: Some Theoretical Ambiguities Marcy K. Uyenoyama and Marcus W. Feldman

CHARACTER: Historical Perspectives Lindley Darden

CHARACTER: Current Usages Kurt Fristrup

COMMUNITY Peter Taylor

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