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AMER. ZOOL., 25:771-777 (1985)
The Evolution of Ecology1
ROBERT K. COLWELL
Department of Zoology, University of California,
Berkeley, California 94720
SYNOPSIS. In spite of an early history of interaction, progress in the fields of ecology and
evolutionary biology during most of this century has been made largely in parallel, with
little creative exchange until the past two decades. In contrast, recent history in the two
fields shows an exciting and productive trend toward a unified effort in understanding
the ecological and evolutionary forces and constraints that together produce the phenomenon of adaptation. Common themes that have drawn the two fields together in the
past decade include an intensified appreciation of discontinuities in time and space, an
increased awareness of the interaction of history and mechanism, a greater concern for
tradeoffs and constraints, and a renewed exploration of the role of hierarchy in producing
pattern.
In the study of biology at the level of
INTRODUCTION
For this 25th Anniversary issue of the individual organisms, there seems to have
American Zoologist I have been asked to give been a fairly steady tradition of evolutionan overview of the recent history and future ary interpretation during this century. In
prospects of ecology. I must begin by contrast, at the levels of populations, comreminding the reader that an "overview" munities, and ecosystems, the history of
is what you get by overlooking things. I evolutionary ideas has often been clouded
have tried to be even-handed, but I have by sloppy thinking and pre-Darwinian
no pretensions to either exhaustiveness or notions of "balance of nature" and of individual or population features evolved "forcomplete objectivity.
the-good-of-the-community"
(Macintosh,
The title of this paper is intended to con1980).
vey a double meaning. As I attempt to map
Darwin himself clearly recognized that
historical shifts in ecology in recent years—
to trace the evolution of the discipline of the determinants of inheritance (whatever
ecology—I will emphasize the increasing they were) were passed from one generaintegration of evolutionary biology and tion to the next by individuals, and framed
ecology—the study of evolution in an eco- his arguments about community dynamics
very clearly to reflect this understanding.
logical context.
Darwin's treatment of the "balance of
nature"—a world view with its roots deep
THE CENTURY AFTER DARWIN
As Macintosh (1980) has recently made in Western history (Simberloff, 1980)—
depicts not a robustly integrated, homeoclear, in a long and scholarly review, early static edifice but a collection of delicately
ecologists viewed the field very clearly in counterpoised elements:
the framework of Darwin's theory of adaptation by natural selection. In Cowles'
In looking at Nature, it is most necessary
(1904) words, "If ecology has a place at all
. . . never to forget that every single
in modern biology, surely one of its great
organic being around us may be said to
tasks is to unravel the mysteries of adapbe striving to the utmost to increase in
tation." Indeed, Harper (1967) has called
numbers . . . . Lighten any check, mitiDarwin himself "the greatest of all ecologate the destruction ever so little, and
gists"—a daunting compliment, if there
the number of the species will almost
ever was one, to us struggling successors.
instantaneously increase to any amount
(Darwin, 1859).
1
Plenary Lecture for the Division of Ecology presented at the Annual Meeting of the American Society of Zoologists, 27-30 December 1984, at Denver,
Colorado.
771
Battle within battle must ever be recurring with varying success; and yet in the
long-run the forces are so nicely bal-
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ROBERT K. COLWELL
and 1970s was very largely based on the
assumptions of demographic and community equilibrium. To make progress mathematically, modelers often assumed that
both components and interactions in communities were homogeneous in space and
In contrast, Clements (1905) saw plant continuous in time (Colwell, 1984). Concommunities themselves as organismic, with sumers were therefore expected to be in
succession as development, and climax as equilibrium with their resources. The veradulthood. The organismic concept of bal and mathematical models of evolutioncommunities and ecosystems has had its ary ecology during this "classical" period
better-known descendents in Allee and of theoretical ecology identify competition
(more recently) the Odums and other pro- for resources, within and between species,
ponents of systems ecology (Macintosh, as the driving force of Darwinian repro1980; Simberloff, 1980). However, this ductive competition. Two of the besttradition is in no way rigorously evolution- developed areas in theoretical ecology—
ary (although there were some attempts at the theory of limiting similarity and optievolutionary formalism [e.g., Dunbar, mal foraging theory—both depend,
I960]). When I was an undergraduate, my implicitly, upon this identification, and
first text in ecology (Odum, 1959) con- mathematical models of coevolution
tained but two references to evolution in the (Roughgarden, 1983) make it explicit.
index (and none to natural selection or adapAs of 1970, theoretical evolutionary
tation)—a brief section on paleoecology,
biology
rested, albeit with increasing disand a figure caption about lichens. At the
comfort,
on its own set of simplifying
population level, the "organismic tradiassumptions
that in many ways paralleled
tion" translated to the notion of "self-regthose
of
theoretical
ecology. Large popuulation" of population densities and other
lations
of
one-locus-two-allele
creatures
features purportedly evolved "for-thetypically
lived
in
a
placid
world
of ontogood-of-the-species" (Wynne-Edwards,
genetic
determinism
and
demographic
sta1962).
bility, homogeneously mixed and evenly
Meanwhile, the 1930s and 1940s had distributed in space, sheltered from the
seen the rise of population genetics as a winds of fortune.
logically rigorous, mathematical treatment
of evolutionary mechanisms (Mayr and
Provine, 1980). Since Gleason (1939), the COMMON THEMES AND CONTACTS IN THE
RECENT HISTORY OF ECOLOGY AND
organismic tradition had had its critics, but
EVOLUTIONARY BIOLOGY
its confrontation with a mature evolutionary biology began in earnest with G. C.
The past ten years have seen many
Williams' Adaptation and Natural Selection changes in population and community
(Williams, 1966, pp. 18-19, 246-250). The ecology, and new currents have moved
maturation of evolutionary ecology as a evolutionary biology as well. In fact, there
discipline owes much to Williams and to are interesting parallels, and the beginthe purge from ecology and behavioral nings of some novel and important interbiology, during the late 1960s and 1970s, actions between the fields. I will try to give
of what D. S. Wilson (1983) calls "naive a rough categorization, with apologies for
group-selectionism." (As far as I can tell, what will no doubt be a highly idiosyncratic
however, systems ecology inexplicably allusion to the enormous literature it covescaped this purge relatively unscathed.)
ers.
Nevertheless, even among evolutionary
ecologists, the balance-of-nature paradigm Intensified appreciation of discontinuities
survived the demise of the related view of in time and space
communities-as-organisms, but in a puriIn both ecology and evolutionary biolfied form: theoretical ecology of the 1960s ogy, population structure has begun to gain
anced, that the face of nature remains
uniform for long periods of time, though
assuredly the merest trifle would often
give the victory to one organic being over
another (Darwin, 1859).
THE EVOLUTION OF ECOLOGY
its rightful leading role in both empirical
studies and conceptual issues. Resource
patterning in space and time is now
regarded as a critical influence on the evolution and ecological functioning of lifehistory traits, social systems, and species
interactions (including competition, predation, parasitism, and mutualism) (Price,
1984). Ecologists have begun to explore in
earnest the role of community substructure or "guild structure" (e.g., Inger and
Colwell, 1977; Holmes et al, 1979; Gilbert,
1980; Pianka, 1980), while evolutionary
biologists undertake the difficult task of
building models that accommodate the
kinds of frequency-dependence that invariably crop up when the assumption of spatial homogeneity is relaxed (Wilson, 1980).
The assumption of homogeneity in time
is also in trouble, and, therefore, so is the
presumption of equilibrium. The possibility that unique, episodic, and catastrophic
events have deeply marked the structure
of communities, the composition of biotas,
and important features of organisms and
their gene pools is now widely acknowledged in both ecology and evolutionary
biology. Disturbance, in the form of such
episodic events as treefalls in forests, storm
damage in intertidal communities, and avalanches on mountainsides, creates a spatial
mosaic of different-aged patches, permits
the persistence of species that are good colonizers but poor competitors in ecological
time, and guides their adaptation in evolutionary time (Paine, 1981; Sousa, 1984).
The question of the role of infrequent and
unpredictable "resource crunches" in
competitive displacement between species
is an important and contentious issue in
community ecology (Weins, 1977; Connell, 1980).
Meanwhile, a parallel conceptual development in paleontology has provided the
stimulus for one of the principal ongoing
debates in evolutionary biology (Eldredge
and Gould, 1972)—the idea that evolutionary history on a geological time scale
may be best characterized as long periods
of stasis punctuated by episodes of relatively rapid evolutionary change. Thus in
both ecology and evolutionary biology, we
have seen the focus shift away from aver-
773
ages toward patterns of variation. However, in my opinion the parallels between
the emphasis on "disturbance" in ecology
and "punctuated" equilibrium in evolution are no more than analogous, because
the time scales are so incommensurate.
An increased awareness of the interaction
of history and mechanism
The projection of past events into the
biological present takes place through
accumulated changes in gene pools, food
webs, biotas, and the organizational aspects
of individual ontogeny, life-history pattern, and community structure. These records of the past are preserved and perpetuated by genes and by their interactions
with the environments their bearers
inhabit. The twin roles of history and
mechanism, or chance and necessity, to use
Monod's (1971) words, have taken an
increasingly central role in both ecological
and evolutionary thinking.
In ecology, there has been a shift toward
a contemporary version of Gleason's (1939)
idea that natural communities are composed of "individualistic" species, each
exploiting the resources for which it is best
suited, with little close integration of species
into communities. At the very least, the
individualistic concept is currently
regarded by many ecologists as a kind of
"null model" for community organization—the case to be disproven with sound
evidence (Harvey et al., 1983). The relative
importance of chance events and species
interactions in the formation of biogeographical patterns has inspired some of the
most heated debates of the past decade
(Strong et al, 1984). Although methodological problems have been the focus of
much of the debate (Colwell and Winkler,
1984), there are substantive biological
issues and important philosophical questions involved as well (Salt, 1984).
In evolutionary biology, the role of
chance events (which may take place either
"gradualistically" or irregularly) has of
course been steadily appreciated, as the
source of raw material for selection. On
the other hand, the past ten years have
produced a strong and effective assault on
the post-Darwinian idea that natural selec-
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ROBERT K. COLWELL
tion is sufficiently omnipotent to guarantee
that every feature of every organism has
an adaptive function—that mechanism
infallibly makes meaning out of chance
events and is unconstrained by history
(Gould and Lewontin, 1979; Gould and
Vrba, 1982). The burden of proof has been
firmly shifted to the proponent of adaptive
explanations for the features of organisms,
populations, communities, or ecosystems.
As in the case of null models in ecology, I
see this approach as a healthy trend toward
higher standards of evidence, and away
from excessive reliance on plausibility
arguments.
A greater concern for tradeoffs
and constraints
The issue of fundamental limits to structure and function is closely related to questions of the role of history in ecology and
evolution. It is not always easy to tell a
tradeoff from a constraint, but the distinction can be drawn. One cold morning this
winter, my nine-year-old daughter, barefoot on the cold linoleum, remarked, "Too
bad we can't walk on the ceiling where the
heat is, like flies do." That even a 60 lb fly
(not to mention a 190 lb one) could not
walk on the ceiling is an insurmountable
constraint of body mass in relation to adhesive and gravitational forces. That mammals warm themselves at rest with metabolic heat (which sets a lower limit on their
size) and flies warm themselves by sitting
on ceilings (which sets an upper limit on
their size) is a tradeoff—and in this case
there is no middle ground.
In biogeography, community composition is constrained by the species pool of
potential colonists, weighted by their vagility (dispersiveness), and by their aptness for
the abiotic and biotic environment. Within
these constraints, chance and interactions
between species are the primary forces at
work. Even when communities in similar
environments can be shown to have converged in important ecological or behavioral characteristics, morphology of the
component species may more closely reflect
the phylogenetic composition of the
regional biota, which constrains the level
of morphological convergence. Darwin's
finches in the Galapagos Islands display an
astonishing diversity of feeding habits with
an absolute minimum of morphological
radiation. Likewise, the lizards of coastal
Chile and coastal California, at similar latitudes and elevations, are remarkably convergent in community structure and in their
use of resources, yet the California fauna,
with several genera and families involved,
is far more diverse morphologically than
the coastal Chilean fauna—virtually all
members of a single genus (Fuentes, 1976,
1980).
"Phylogenetic constraints" have also
taken their rightful place among the factors considered important in the evolution
of form and function in a more general
sense. Gould and Lewontin (1979) state the
principle provocatively:
. . . organisms must be analyzed as integrated wholes, with Baupldne so constrained by phyletic heritage, pathways
of development and general architecture that the constraints themselves
become more interesting and more
important in delimiting pathways of
change than the selective force that may
mediate change when it occurs.
The "tradeoff principle" is hardly new
to ecology, but there has been a continual
accumulation of documented empirical
examples and theoretical applications, particularly in life-history theory and foraging
theory. For instance, the discovery that territorial hummingbird species tend to have
a higher wing-loading (that is, they are
heavier for their wing span) than circuitforaging, non-territorial hummingbirds is
neatly explained by a tradeoff between
flight efficiency and effectiveness in aerial
combat. Like a fighter airplane, a territorial species pays with higher "fuel" consumption, per gram per second, for the
maneuverability and acceleration it gains
from its shorter wings. For the same body
weight, the longer-winged circuit-forager,
like a transport plane, is less maneuverable
than a territorialist but can go farther on
the same amount of fuel, thereby exploiting widely spaced flowers that the territorialist finds uneconomical to defend
(Feinsinger et al., 1979).
THE EVOLUTION OF ECOLOGY
In evolutionary biology, the emergence
of quantitative genetics as a tool in the
analysis of evolutionary patterns in nature
(e.g., Arnold, 1983) promises to give us a
rigorous basis for understanding certain
kinds of evolutionary tradeoffs. These
techniques aim to untangle conflicting
selective demands (for example, between
sexual selection and escape from predation), as well as the role of pleiotropy,
allometry, and other sources of correlated
response to selection.
The current burst of interest in "scaling" (e.g., Peters, 1983; Schmidt-Nielsen,
1984)—the structural and functional consequences of size differences among organisms that share a basic design—grew out
of an important tradition in evolutionary
biology (Thompson, 1917, 1961). Like the
story I told about flies on the ceiling, which
was a question of scaling and functional
design, the scientific study of size, form,
and function revolves around the study of
constraints and tradeoffs. The application
to biology of principles from engineering
and materials science in the growing field
of biomechanics (Wainwright et al, 1976),
together with the study of allometry (relationships between size and shape) within
the tradition of evolutionary biology
(Gould, 1966), have led to a growing point
between ecology and evolution that holds
great promise for the study of adaptation
in both its meanings—as an evolutionary
process and as an ecological consequence.
A renewed exploration of the role of
hierarchy in producing pattern
In ecology, the importance of hierarchy
is most obvious in competitive interactions
(both within and between species) in interactions among trophic levels, and in the
interaction of competitive and trophic
relations. Darwin (1859) performed the
first field experiment (as far as I can ascertain) that revealed the operation of this
class of phenomena:
If turf which has long been mown, and
the case would be the same with turf
closely browsed by quadrupeds, be let to
grow, the more vigorous plants gradually kill the less vigorous, though fully
775
grown, plants: thus out of twenty species
growing on a little plot of turf (three feet
by four) nine species perished from the
other species being allowed to grow up
freely . . . . The amount of food for each
species of course gives the extreme limit
to which each can increase; but very frequently it is not the obtaining food, but
the serving as prey to other animals,
which determines the average numbers
of a species.
As a general principle, the action of consumers (or certain kinds of disturbance) can
mitigate competition among resource
species, as Darwin showed by preventing
"herbivory" (mowing) in his lawn experiment. However, experimental and theoretical work during the past two decades
has revealed that the outcome of non-random predation depends critically on the
underlying competitive relations among the
prey species. Whether or not a set of prey
species forms a "transitive" competitive
hierarchy is a key issue in the assessment
of community dynamics (Sousa, 1984).
An historically separate approach to
some of the same phenomena is gathering
steam under the aegis of "food web theory" (Cohen, 1978; Pimm, 1982). Again,
the analysis of hierarchy in relation to
interactions within levels unites these
endeavors with other currents in ecology
and evolutionary biology. Allen and Starr
(1982) have opened yet another door on
the problem of ecological complexity
through the application of hierarchy theory.
Meanwhile, evolutionary biology has
been undergoing a significant rebirth, or
perhaps, at last a legitimate birth, of the
application of hierarchical selection theory
to behavioral and life-history characteristics of organisms, and to coevolution
between species in a community context.
The words "group selection" are once
again greeted with cautious interest, rather
than outright scorn (Wilson, 1983).
Emphasis on the differential productivity
of groups, rather than the differential extinction of groups (as in the classical theoretical treatments), has revitalized modelling in this area, and has permitted the first
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ROBERT K. COL WELL
successes in applying hierarchical selection
theory to field data, especially the area of
the evolution of sex ratio (Colwell, 1981;
Wilson and Colwell, 1982; Frank, 1985a,
b). T h e cautious extension of these
approaches to interspecific associations in
nature {e.g., Wilson, 1984), though still in
its infancy, can be viewed as a promising
step toward a qualified and rigorous reinstatement of the "community as organism," stripped of its mystical trappings.
IN PROSPECT
In a recent New Yorker cartoon by Charles
Addams, a beaver and a rabbit sit on the
bank down-river from the base of a towering concrete hydroelectric dam that fills
the canyon upstream. The beaver says to
the rabbit, "I didn't actually build it, but it
was based on my idea." The fact that many
of the same design principles are critical to
the success of both beaver dams and human
ones is obvious even to the layperson, and
underlies the humor in the beaver's boastfulness. Not even the most ardent skeptic
among professional biologists would doubt
that the complex behavior of dam-building
in beavers is an adaptation produced by the
creative force of natural selection in the
setting of the beaver's environment. But
how did the unique habits of the beaver
evolve? In the absence of historical information, this question can be answered only
by the study of living beavers—their size
and body form, their life history, their individual and social behavior, the patterning
of their relations with food and enemies in
both space and time, and the correspondence of these features with parallels in
other rodents as well as in more distant
lineages.
Cowles' (1904) notion that the role of
ecology is to "unravel the mysteries of
adaptation" has begun to come of age,
along with the coordinate role of evolutionary biology in revealing how the process of evolution transforms the ecology of
individual organisms, populations, and
communities. The future holds the exciting prospect of a continued growingtogether and creative interaction between
the fields of ecology and evolutionary biology-
REFERENCES
Allen, T. F. H. and T. B. Starr. 1982. Hierarchy.
Perspectives for ecological complexity. University of
Chicago Press, Chicago.
Arnold, S. J. 1983. Sexual selection: The interface
of theory and empiricism. In P. Bateson (ed.),
Mate choice, pp. 67-107. Cambridge University
Press, Cambridge.
Clements, F. E. 1905. Research methodsin ecology. Univ.
Publ. Co., Lincoln, Neb.
Cohen, J. E. 1978. Food webs and niche space. Princeton University Press, Princeton, N.J.
Colwell, R. K. 1981. Group selection is implicated
in the evolution of female-biased sex ratios. Nature
290:401-404.
Colwell, R. K. 1984. What's new? Community ecology discovers biology. In P. W. Price, C. N. Slobodchikoff, and W. S. Gaud (eds.), A new ecology:
Novel approaches to interactive systems, pp. 387—397.
Wiley, New York.
Colwell, R. K. and D. W. Winkler. 1984. A null model
for null models in biogeography. In D. R. Strong,
Jr., D. Simberloff, L. G. Abele, and A. B. Thistle
(eds.), Ecological communities: Conceptual issues and
the evidence, pp. 344-359. Princeton University
Press, Princeton, N.J.
Connell, J. H. 1980. Diversity and the coevolution
of competitors, or the ghost of competition past.
Oikos 35:131-138.
Cowles, H. C. 1904. The work of the year 1903 in
ecology. Science 19:879-895.
Darwin, C. 1859. The origin of species. John Murray,
London.
Dunbar, M. J. 1960. The evolution of stability in
marine environments: Natural selection at the
level of the ecosystem. Amer. Natur. 94:129136.
Eldredge, N. and S.J. Gould. 1972. Punctuated equilibria: An alternative to phyletic gradualism. In
T. J. M. Schopf (ed.), Models in paleobiology, pp.
82-115. W. H. Freeman, San Francisco.
Feinsinger, P., R. K. Colwell, J. Terborgh, and S. B.
Chaplin. 1979. Elevation and the morphology,
flight energetics, and foraging ecology of tropical
hummingbirds. Amer. Natur. 113:481-497.
Frank, S. A. 1985a. Hierarchical selection theory
and sex ratios. I. General solutions for structured
populations. Theor. Pop. Biol. (In press)
Frank, S. A. 1985*. Hierarchical selection theory
and sex ratios. II. On applying the theory, and a
test with fig wasps. Evolution. (In press)
Fuentes.E. R. 1976. Ecological convergence of lizard
communities in Chile and California. Ecology 57:
3-17.
Fuentes, E. R. 1980. Convergence of community
structure: Neutral model vs. field data. Ecology
61:198-200.
Gilbert, L. E. 1980. Food web organization and the
conservation of neotropical diversity. In M. E.
Soule and B. A. Wilcox (eds.), Conservation biology,
pp. 11-33. Sinauer Associates, Sunderland, Mass.
Gleason, H. A. 1939. The individualistic concept of
the plant communit). Amer. Midi. Natur. 21:92110.
T H E EVOLUTION OF ECOLOGY
777
In D. J. Futuyma and M. Slatkin (eds.), CoevoluGould, S. J. 1966. Allometry and size in ontogeny
tion, pp. 33-64. Sinauer Associates, Sunderland,
and phylogeny. Biol. Revs. 41:587-640.
Mass.
Gould, S.J. and R. C. Lewontin. 1979. The spandrels
of San Marcos and the Panglossian paradigm: A Salt, G. W. (ed.) 1984. A round table on research m
critique of the adaptationist programme. Proc.
ecology and evolutionary biology. University of Chicago Press, Chicago.
R. Soc. Lond. B 205:581-589.
Gould, S. J. and E. S. Vrba. 1982. Exaptation—A Schmidt-Nielsen, K. 1984. Scaling. Cambridge Unimissing term in the science of form. Paleobiology
versity Press, Cambridge.
8:4-15.
Simberloff, D. S. 1980. A succession of paradigms in
ecology: Essentialism to materialism and probaHarper, J. L. 1967. A Darwinian approach to plant
bilism. Synthese 42:3-39.
ecology. J. Ecol. 55:247-270.
Harvey, P. H., R. K. Colwell, J. W. Silvertown, and Sousa, W.P. 1984. The role of disturbance in natural
communities. Ann. Rev. Ecol. Syst. 15:353-391.
R. M. May. 1983. Null models in ecology. Ann.
Strong, D. R., Jr., D. Simberloff, L. G. Abele, and A.
Rev. Ecol. Syst. 14:189-211.
Holmes, R. T., R. E. Bonney, Jr., and S. W. Pacala.
B. Thistle, (eds.) 1984. Ecological communities:
Conceptual issues and the evidence. Princeton Uni1979. Guild structure of the Hubbard Brook bird
versity Press, Princeton, N.J.
community: A multivariate approach. Ecology 60:
512-520.
Thompson, D. W. 1917. On growth and form. CamInger, R. F. and R. K. Colwell. 1977. Organization
bridge University Press, Cambridge.
of contiguous communities of amphibians and Thompson, D. W. 1961. On growth and form.
(Abridged edition.) Cambridge University Press,
reptiles in Thailand. Ecol. Monogr. 47:229-253.
Macintosh, R. P. 1980. The background and some
Cambridge.
current problems of theoretical ecology. Synthese Wainwright, S. A., W. D. Biggs, J. D. Currey, andj.
43:195-255.
M. Gosline. 1976. Mechanical design in organisms.
Mayr, E. and W. B. Provine. 1980. The evolutionary
Edward Arnold, London.
Weins.J. A. 1977. On competition and variable envisynthesis. Harvard, Cambridge, Mass.
Monod, J. 1971. Chance and necessity. A. A. Knopf,
ronments. Amer. Scientist 65:590-597.
New York.
Williams, G. C. 1966. Adaptation and natural selection.
Odum, E. P. 1959. Fundamentals of ecology. W. B.
Princeton University Press, Princeton, N.J.
Saunders, Philadelphia.
Wilson, D. S. 1980. The natural selection of populations
Paine, R. 1981. The forgotten roles of disturbance
and communities. Benjamin/Cummings, Menlo
Park, Calif.
and predation. Paleobiology 7:553-560.
Peters, R. H. 1983. The ecological implications of body
Wilson, D. S. 1983. The group selection controversy:
History and current status. Ann. Rev. Ecol. Syst.
size. Cambridge University Press, Cambridge.
Pianka, E. P. 1980. Guild structure in desert lizards.
14:159-187.
Oikos 35:194-201.
Wilson, D. S. 1985. Adaptive indirect effects. In T.
Pimm, S. L. 1982. Food webs. Chapman and Hall,
Case and J. M. Diamond (eds.), Ecological comLondon.
munities. Harper and Row, New York. (In press)
Price, P. W. 1984. Alternative paradigms in com- Wilson, D. S. and R. K. Colwell. 1982. Evolution of
munity ecology. In P. W. Price, C. N. Slobodsex ratio in structured demes. Evolution 35:882—
chikoff, and W. S. Gaud (eds.), A new ecology: Novel
897.
approaches to interactive systems, pp. 353-385. Wiley, Wynne-Edwards, V. C. 1962. Animal dispersion in
New York.
relation to social behavior. Oliver and Boyd, EdinRoughgarden, J. 1983. The theory of coevolution.
burgh.