Download Interspecific Competition and Species` Distributions

AMER. ZOOL., 21:889-901 (1981)
Interspecific Competition and Species' Distributions:
The Ghosts of Theories and Data Past1
JEREMY B. C. JACKSON
Department of Earth and Planetary Sciences, The Johns Hopkins University,
Baltimore, Maryland 21218
SYNOPSIS. The idea that biological interactions between species restrict their distributions
beyond limits set by the inorganic environment was established by plant ecologists well
before the work of Volterra, Gause, and the development of modern niche theory. Mechanisms of competition between plant species, and the influence of predation and environmental factors on the outcome of interspecific competition, were demonstrated by
extensive field experiments. These early botanical achievements were ignored by zoologists
whose subsequent, independently derived ideas about competition paralleled those of
plant ecologists to a remarkable degree. Application of niche theory to the real world was
closely tied to the advent of the "modern synthesis." The primary innovation of niche
theory was not simply a new appreciation of the possible importance of competition between animals, but the incorporation of an evolutionary perspective to distributional problems largely absent among ecologists since Darwin.
INTRODUCTION
The role of competition between species
in affecting their distributions is today hotly debated in many quarters (e.g., Connell,
1975, 1978, 1979, 1980). Regardless of position, these discussions almost invariably
focus on the Volterra-Gause niche theory
of competition and the principle of competitive exclusion, as if the importance of
interspecific competition rises or falls on
the strengths or weaknesses of these points
of view (e.g., Hutchinson, 1975, 1978;
Strong, 1979; Heck, 1980). In 1978, for
example, Jared Diamond published a paper titled "Niche shifts and the rediscovery
of interspecific competition, why did field
biologists so long overlook the widespread
evidence for interspecific competition that
had already impressed Darwin?" According to Diamond, ecologists before 1959
missed the boat because, among other reasons:
1. They did not know what to look for.
2. They did not understand the niche concept.
3. They were misguided reductionists
searching solely for physical explanations.
4. They did not have a theoretical framework for the information they did not
know how to look for.
In this paper I will demonstrate that Diamond's story simply is not true. Rather,
ecologists long before 1959 thought a
great deal about competition, they did
know what to look for, they were not all
"reductionists," they did not need a mathematical formulation of the niche to have
the same idea, and they had a well developed theoretical framework, namely
succession. The fact that their theory was
wrong by current views is immaterial; it
stimulated a great deal of important work.
At this point it is probably worth saying
that I was reared on Hutchinsonian niche
theory and, unlike many ecologists today,
still find it enormously stimulating. My argument here is simply against a misguided
sense of the originality of ideas characteristic of the revisionist history written by
successful, creative scientists. I will proceed as follows:
1. Outline what I take to be the generally
accepted genealogy of niche theory
pre-1960.
2. Summarize what was actually being
published in the principal English-language
ecological journals of the time.
1
From the Symposium on Theoretical Ecology preIdeas
about fundamental versus resented at the Annual Meeting of the American Soalized niches, and the roles of compeciety of Zoologists, 27-30 December 1980, at Seattle,
tition and other processes in shaping
Washington.
889
890
JEREMY B. C. JACKSON
Population
Genetics
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Mathematical Pooutation
I92O'S
Ecology
(PEARL, VOLTERRA, LOTKA)
(FISHER, WRIGHT, HALOANE)
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"Modern Synthesis"
(HUXLEY, MAYR. 006ZHANSKY)
I930'S-(940'S
Laboratory Experimental
(GAUSE, PARK, CROM8IE)
Distributions of Natural Populations
(HUTCHINSON and LACK)
I940'S-I950'S
1
1
1960's
Modern Niche Theory
FIG. 1. Partial genealogy of modern niche theory
pre-1960. Details of right side of figure in Hutchinson (1975, 1978).
species distributions, have a considerable pedigree.
3. Point out what was apparently new with
modern niche theory, namely an evolutionary perspective regarding distributional problems.
Lack's first great contributions on this topic are his 1944 paper "Ecological aspects of
species formation in passerine birds" and
its subsequent expanded version, his 1947
book Darwin's finches. In these works Lack
focused on the role of competition in shaping distributions of closely related bird
species and developed his now famous axiom that, because of competition, such
species are either allopatric, or if sympatric, live in different microenvironments
and/or eat different foods. His debt to the
modern synthesis is clear. Mayr and Huxley seem to have influenced him more than
Gause, and he says of Huxley (1942) that
he
". . . is apparently the only previous
worker to suggest that these differences
in size are primarily correlated with differences in food." (Lack, 1944, p. 279)
Lack (1944, p. 284) acknowledged Huxley
for his "extensive criticism of both the facts
According to Diamond (1978), Hutch- and views here expressed, which were ininson (1975, 1978), and others, the path to valuable in completing the final draft." Beunderstanding of the ecological impor- fore 1944 Lack had seemingly no interest
tance of interspecific competition looks in competition and believed that bird
something like the right hand side of Fig- species distributions were explainable by
ure 1. This story, that mathematical habitat selection (Lack, 1933). How such
models stimulated laboratory experiments habitat selection might have evolved apwhich in turn stimulated understanding of parently did not interest him until he
the real world, is the way interspecific com- abandoned the hypothesis as evolutionarpetition is commonly introduced in basic ily unsound in 1940.
texts (e.g., Krebs, 1972). The left hand side
Hutchinson's (1941, 1944) seminal paof Figure 1 is usually ignored, yet, as we pers dealt with the role of competition in
shall see, the "modern synthesis" was es- plankton succession in lakes. In these pasential to what Lack and Hutchinson had pers he cited Volterra and Gause but igto say. I will not discuss the history before nored the botanical literature despite the
Hutchinson and Lack as it is widely known obsession of plant ecologists with succes(see especially Hutchinson, 1975, 1978). sion at that time. In his famous 1951 paper
One point however, deserves special men- "Copepodology for the ornithologist"
tion here. Gause himself did only labora- Hutchinson cited Lack and Huxley. There
tory experiments, but in his influential and in his later paper on the niche (1958)
1934 book The strugglefor existence, he care- and "Homage to Santa Rosalia" (1959)
fully reviewed much of what was already there is no mention of terrestrial plant
known of competition in the real world. ecology. The same is true of all Lack's
This chapter is largely one of plant-envy, works on interspecific competition.
for Gause knew what most ecologists have
Through these papers of Hutchinson
since forgotten, namely that a great deal and Lack, niche theory became firmly eswas known of competition among plants.
tablished among ecologists. Consequently
Hutchinson and Lack were the first to views of competition became strongly
successfully apply ideas of competitive ex- biased in at least two ways. First, competiclusion to the real world in a big way. tion between species became equated with
GENEALOGY OF MODERN NICHE THEORY
891
INTERSPECIFIC COMPETITION
THE PUBLISHED RECORD OF COMPETITION
STUDIES BEFORE 1959
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the niche theory of Volterra and Gause.
Second, all questions about competition
that came to be considered interesting
were denned for the equilibrium case.
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ogists who were writing during the time of
1915
1925
1936
1945
1955
the scenario just described. Data are from
YEAR
the three original English-language ecoFie. 2. Number of published papers mentioning inlogical journals, Journal of Ecology (JE- terspecific
competition as a factor influencing organCOL), Journal of Animal Ecology (JAE) and ism distributions per 1,000 journal pages from 1920Ecology (ECOL), plus The American Natu- 1959. Data points for five-year intervals (e.g., 1920—
ralist (AMNAT). The period covered is the 1924, 1925-1929, etc.). P = JECOL (Journal of Ecolforty years previous to and including publi- ogy), A = JAE (Journal of Animal Ecology), and E =
cation of Hutchinson's "Homage to Santa ECOL (Ecology).
Rosalia" (except for JAE which began publication in 1932). I read at least the summary and scanned every article for any ref- These are, in order of numbers of papers:
erence to interspecific competition as a 1. Studies of distributions for their own
distributional factor. Indices to the joursake: 36% of 332 papers. These include
nals are unfortunately incomplete and/or
Eltonian animal ecology and much
unreliable. For example, Hutchinson's
plant ecology not directly concerned
(1951) "Copepodology for the ornitholowith succession theory. There is no
gist" and MacArthur's (1958) "Population
temporal trend in the frequency of this
ecology of some warblers of northeastern
group of papers in JAE (Fig. 3A); there
coniferous forests" are not listed under
is an increase in JECOL and perhaps in
competition in the Ecology index.
ECOL with waning interest in plant
succession.
There are 336 papers that deal in some
way with interspecific competition in 2. Applied research: 31% of 332 papers.
These include, for example, papers by
71,610 pages of the four journals from
plant ecologists trying to save the
1920-1959. Of these, only fourteen are
American prairie and tropical biologists
from AMNAT, many of whose authors
concerned with parasites and disease.
were busy inventing population genetics
There is a general peak (Fig. 3B) in this
and the "modern synthesis." Excluding
group of papers in the interval 1940AMNAT, there are 322 papers in 50,436
1945, apparently reflecting previous
journal pages or 6.4 articles on interspenatural disasters rather than the ongocific competition for every thousand pages
ing war.
in the three major ecological journals of
the time. That is quite a lot! So, right away,
Neither of these first two groups of pawe can dismiss Diamond's (1978) claim
that ecologists were not studying interspe- pers could be said to be directly motivated
cific competition before 1959. There is not by theory at all.
even any reasonable temporal trend in the 3. Successionists, in the sense of Clements
number of papers (Fig. 2).
and Tansley: 30% of 332 papers. Authors of papers in this group also wrote
What were these authors thinking about
many papers in the first two groups. Bewhile studying interspecific competition so
lief in succession necessitated belief in
enthusiastically? The papers fall readily
competition as the driving force of sucinto four slightly overlapping groups (so
cession, and many were interested in
they sum to slightly more than 100%).
HI
JEREMY B. C. JACKSON
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1945
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Fie. 3. Intellectual framework of papers mentioning interspecific competition published from 1920-1959.
A, studies of distributions for their own sake; B, applied research; C, studies invoking succession theory;
D, studies invoking niche theory. A-C for P = JECOL, A = JAE, and E = ECOL; D as for above plus
N = AMNAT (American Naturalist).
er and editor of the journal since its inception in 1914. A. S. Watt and E. J. Salisbury
were also influential contributors. The
quality of papers in this period was consistently excellent by modern standards.
There followed a lapse in the 1930s of primarily descriptive vegetation studies, apparently motivated by a rather uncritical
but abiding faith in community succession.
After this, there emerged an important series of papers by A. S. Watt and others on
pattern and process in plant communities.
When ECOL first appeared in 1920 it
The primary theme in JECOL until the
early 1930s was succession, and the domi- was, like JECOL, primarily a botanical
nant figure was Sir Arthur Tansley, found- journal. Succession was again the major
observing or measuring this force.
There is a sharp decline in the frequency
of such papers (Fig. 3C) with declining
interest in plant succession itself.
4. Volterra-Gause niche theory: 13% of
332 papers. This, by far the smallest
group, includes authors in the tradition
of the right side of Figure 1. There are
slow increases in the frequencies of papers in this group in ECOL and JAE, no
papers at all in JECOL, and a striking
increase in AMNAT (Fig. 4D).
INTERSPECIFIC COMPETITION
theme, and F. E. Clements the dominant
figure, though he published few papers in
the journal. In the 1930s management of
the prairie became a major topic along
with succession. Later still there was no
unifying theme or dominant figure evident.
JAE was Charles Elton's journal. He
founded it to get out from under the
thumb of the plant ecologists. The early
theme of the journal was causes of variations in animal numbers through time.
This came straight from his 1927 book
Animal ecology, the introduction to chapter
9 of which reads:
"The numbers of animals never remain
constant for very long and usually fluctuate considerably and rather regulariy-"
Contrast this with the first sentence of
Lack's 1954 book The natural regulation of
animal numbers.
"Most wild animals fluctuate irregularly
in numbers between limits that are extremely restricted compared with what
their rates of increase would allow."
Between these two divergent statements,
in 1944, was the famous British Ecological
Society symposium on Gause's work and
the ecology of closely related species.
About this time Elton became more interested in competition than he was in 1927
(Elton, 1946), but not in the same way as
Lack, who wrote numerous niche theorycompetition papers after 1944 (e.g., Lack,
1945, 1946). In 1954, Elton and Miller
considered Lack's approach, said it had
merit, but complained of lack of tests for
his ideas and appealed for experiments
comparable to those done for plants that
Lack and Hutchinson ignored. As an example of what could be done, Elton and
Miller praised Brian's (1952) experimental
study of interspecific competition in ants.
Let us summarize what we have discovered so far relative to Diamond's (1978)
scenario. First, there was a great deal of
work on interspecific competition before
niche theorists (in the current sense) got
around to it. Second, much of this work
was stimulated by a simple desire to un-
893
derstand distribution patterns for their
own sakes, or to solve practical problems,
without regard to any theoretical framework. Third, most of the work on interspecific competition that was stimulated by
theory had another theoretical perspective, now much out of favor, i.e., plant
succession. Evidently dislike (e.g., Hutchinson, 1940) of the superorganism point of
view regarding succession and its proponents' pervading fascination with community classification prevented modern niche
theorists from recognizing the considerable accomplishments of these plant ecologists. This is interesting because much of
what is considered original to modern
niche theory of competition, except the
mathematics, was well formulated and
understood by many plant ecologists, especially in England, as early as 1914. I will
demonstrate this in some detail for two
subjects of major interest both to early
plant ecologists and most ecologists today.
• These are (i) the concepts of what are now
called fundamental versus realized niches
and (ii) the interacting roles of competition, predation, and physical disturbance
in determining community structure.
EARLY PLANT ECOLOGISTS' CONCEPTS
OF THE NICHE
Ideas virtually identical to Hutchinson's
(1958) concept of the niche were put forth
by prominent, well-known, and influential
British plant ecologists more than forty
years before the Cold Spring Harbor Symposium. The first clear statement is that of
Tansley (1914) in his presidential address
to the first annual meeting of the British
Ecological Society. In his paper Tansley
defined the field of ecology as he saw it. In
a section titled "Competition and Succession" he says (p. 198):
One of the most important factors which
will be at once met with in this field is
competition, the competition of plants
of the same species and of plants of different species growing in the same community. A closed plant community, such
as a wood or a meadow or a heath, is
generally relatively stable apart from human interference. That is not to say that
894
JEREMY B. C. JACKSON
it is not undergoing change, but the
change is comparatively slow. The plant
population is in a condition of relative
equilibrium. The balance between its
different members has been worked out,
and fresh invaders can only gain an entrance sporadically. In such conditions
competition, though it is by no means in
abeyance, is largely masked. In order to
determine the powers of the different
species, we must resort to experiment,
i.e. we must give the individuals of the
various species a freer field than they
have in the restricted conditions of a
closed association. The simplest way in
which this can be done is by clearing a
patch of ground of some or all of the
species present and seeing what happens. By suitable modifications of this
procedure we should be able to disentangle the factors which have led to the
actual distribution of species in—that is,
to the structure of—the closed association. We shall find that it depends on
several factors. In the first place the general habitat conditions, depending primarily on the nature of the soil, determine what species can [Tansley's italics]
exist in a given spot. Secondly, we have
to determine what species can actually
gain access to the spot by seeds or other
propagative organs, and having gained
access whether they can germinate and
establish themselves.
This is a remarkably modern outlook. Besides appealing for experiments, to which
we shall return, note that Tansley is thinking in terms of equilibria for most plant
communities. He did, however, recognize
the importance of communities "in which
the habitat is constantly and rapidly changing, so that equilibrium cannot be established" (p. 199). This is "The paradox of
the plankton" (Hutchinson, 1961) in 1914.
Note also that Tansley made a clear and
deliberate distinction between what
Hutchinson (1958) termed the fundamental versus the realized niche when he contrasted "what species can exist in a given
spot," which he defines largely in terms of
soil conditions, and "what species can actually gain access to the spot . . . and . . .
can germinate and establish themselves."
This distinction has been a major theme in
British plant ecology ever since. For example, Tansley (1917) reported results of
an experimental study of competition between two species of the bedstraw Galium
(see also Hutchinson, 1978). Tansley
showed that both species could live on calcareous soils and peat but that the outcome
of competition resulted in different dominants in the two soil types, i.e., it was not
sufficient to know under what conditions
a plant could live alone, but also where it
could survive amongst other plants.
In 1929, E. J. Salisbury gave his presidential address to the British Ecological
Society in which he wrote (p. 201):
. . . culture of plants in conditions far
removed from those of their natural
habitats is possible with a large number
of species provided always that the surrounding soil is kept sedulously weeded.
Such facts emphasize how delicate is the
balance between species in the struggle
for supremacy and how an adverse condition even far removed from the lethal
point may weight the scale in one direction or the other.
It is not my purpose to treat here of
the relation of species to the external
factors of the habitat, though it is obvious that before we are in a position to
assess the contributory causes of dominance and subordination of species their
optimal requirements as regards light,
water supply, soil reaction, supply of essential nutrients, etc. will have to be determined. The more nearly the habitat
conditions simultaneously approach the
optimum requirements for a given
species in these several respects the less
susceptible will it be to suppression by its
competitors unless the same conditions
bring about a corresponding increase in
their vigour also.
Thus for Salisbury, as for Gause (1934)
and others later on, the more similar two
species' requirements, the more intense
was competition likely to be between them.
Interest in potential versus realized occurrences of plants continued in a big way.
The British Ecological Society funded a
895
INTERSPECIFIC COMPETITION
major experimental investigation of the
range of physical and chemical environmental conditions under which common
British plant species could survive. For this
purpose they did transplant experiments,
bringing together plants from all over
Britain to a single place where soils, watering, and nutrients could be varied in a systematic and controlled fashion. In the first
report of this work Marsden-Jones and
Turrill (1930) point out that the plants
were deliberately grown in the absence of
competitors to test the importance of what
they termed "edaphic factors," i.e., they
were determining the boundaries of the
species' fundamental niches. This was expensive work done on a massive scale for
more than a decade; obviously the members of the Society thought it was important.
Early plant ecologists also considered
mechanisms of competition between plants
(Clements and Weaver, 1924; Clements et
al, 1929; Salisbury, 1929). Three questions of particular interest were (i) the relative importance of competition for light
versus that for soil, water and nutrients,
usually termed shading versus root competition (e.g., Moore, 1929); (ii) why particular soils like the English chalk favored
one species or another, e.g., the reasons
for the outcome of Tansley's (1917) experiments (Salisbury, 1920; Rayner, 1921);
and (iii) how established plants prevented
others from becoming established by preventing their seeds from reaching the soil
or germinating (Cameron, 1935). To these
ends plant ecologists did numerous laboratory and field experiments. By laboratory experiments I mean manipulative
plantings in greenhouses or field. In these
they varied plant densities, species compositions, and resources such as light, minerals, or water. Field experiments (sensu
Connell, 1974; Paine, 1977) comprised
manipulations of natural communities,
usually with care to change only a single
factor. For example, ditches were dug to
separate the roots of different plants while
still allowing them to potentially shade
each other (Fricke, 1904 (not seen, cited in
Connell, 1975); Fabricus, 1927 (not seen,
cited in Salisbury, 1929); Phillips, 1928;
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1925
1935
1945
1955
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1955
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1915
1925
YEAR
Fic. 4. Percentage of papers mentioning interspecific competition based on (A) field experiments or
(B) field experiments and/or observations of displacement of one species by another. P = JECOL, A =
JAE, and E = ECOL.
Tourney, 1928; Holch, 1931; Toumey and
Kienholz, 1931; Watt and Fraser, 1933;
Korstian and Coile, 1938; Lutz, 1945;
Shirley, 1945; Robertson, 1947; McVean,
1956; Ellison and Houston, 1958). They
also selectively shaded plants (Phillips,
1928; Nedrow, 1937; Harley, 1939; Chapman, 1945; Ellison and Houston, 1958)
and examined competition between established and newly germinating plants (Cameron, 1935; Bramble and Goddard, 1942).
Many of the first experiments were not
properly controlled or replicated, but over
time many became quite sophisticated.
None other than R. A. Fisher more or less
invented Latin squares and parametric statistics for agriculturalists, and many plant
896
JEREMY B. C. JACKSON
ecologists followed suit with some truly sophisticated work (e.g., Summerhayes,
1941; Bramble and Goddard, 1942).
Because of the great importance currently attached to field experiments (Colwell and Fuentes, 1975; Connell, 1974,
1975, 1978, 1979, 1980; Paine, 1977;
Strong, 1979; Heck, 1980), and widespread belief in their novelty, it is worth
considering the extent of earlier similar
work. Some 78 of the 322 interspecific
competition papers published in JECOL,
JAE, and ECOL from 1920 to 1959 involved field experiments. Two hundred
and nine involved plants, and of these 70
or 34% used or explicitly referred to results of field experiments. In contrast, of
the 113 papers about animals, only eight
or 7% used field experiments. The patterns over time for the three journals are
shown in Figure 4A. Percentages of papers
utilizing field experiments were always
20% or more in the plant journals (JECOL
and ECOL) and much lower in JAE. Expanding the criterion of reasonable demonstration of competition in nature to include carefully observed displacements of
species by others (see Connell, 1975), the
percentages are higher overall, but are still
lower for animals than for plants. These
differences apparently reflect differences
in scientific attitudes of plant and animal
ecologists of the time as much as greater
difficulties of working with highly mobile
animals such as birds.
Plant ecologists worried about the validity of their techniques and even wrote
"methods" papers. For example, in his paper "Exclosure technique in ecology,"
Daubenmire (1940) comments on problems of what are now called "cage effects"
and their interpretation (apparent versus
real causes of results). Certainly there is no
support here for the view of Connell
(1975, 1978, 1979, 1980) and others today
that reliable field demonstrations of interspecific competition are lacking.
Another recent issue (e.g., Sanders,
1968; Paine, 1974) involves the relative importance of biological versus physical factors in distributions of marine organisms.
Early plant ecologists envisioned no such
dichotomy. Rather they designed their
competition experiments to bring out the
subtle relationships between so-called
edaphic factors such as soil pH and the
outcome of competition. To quote Salisbury (1929, p. 199): " . . . the vigour of a
species and its consequent capacity for
dominance may depend on apparently
quite small and insignificant changes in the
environment and provides a salutory
warning against neglecting such as unimportant." Thus a large number of plant
ecologists studied gradients in environmental conditions not because they were
misguided reductionists unaware of competition, but because they knew the complexity of the multitudinous interactions
hidden behind that name. Certainly the
same must be true of physical gradients on
rocky shores.
COMPETITION, PREDATION, DISTURBANCE,
AND DIVERSITY
A second area long of interest to plant
ecologists involves the nature of the combined effects of competition, predation,
and physical environmental disturbances
on plant community structure and diversity. From the beginnings of this century,
British and American plant ecologists,
farmers, and ranchers have been impressed by the effects of herbivores on the
composition of vegetation, especially in
heaths, fields, and the American prairie.
To quantify the nature and magnitude of
these phenomena they did many field experiments, mostly using exclosures (Farrow, 1916, 1917, 1925; Watt, 1923, 1934,
1957; Tansley and Adamson, 1925; Taylor, 1930; Talbot etai, 1939; Daubenmire,
1940; Godwin, 1941; Hope-Simpson,
1941; Summerhayes, 1941; Bramble and
Goddard, 1942; Fitch and Bentley, 1949;
Gimingham, 1949; Gillham, 1953, 1955;
Goodman and Gillham, 1954). The scale
of manipulations ranged from modest
cages to entire forests and fields. As before, many of the early experiments were
lacking in details of design, but many of
the later studies were excellent.
The nearly universal result of exclosures
was a dramatic change in dominant plant
897
INTERSPECIFIC COMPETITION
species. Sometimes replacement was merely of one grass or herb by another, but other times, especially for exclosures maintained ten to twenty years, trees or woody
shrubs began to replace grasses or ferns
(Farrow, 1941; Hope-Simpson, 1941).
These studies were not done just to
demonstrate the processes of competition
or predation in nature. Everyone seems to
have accepted the importance of both as
obvious. Rather, they were designed to unravel the extent of effects, the mechanisms
of their action, and their consequences in
shaping the major vegetational features of
England and the American west. They
were also done to determine how commercially important pasture and range
were being ruined by drought and/or overgrazing and what to do about it. Ranchers, for example, worried about the possible worth in cattle forage of consumption
of vegetation by rodents (Taylor, 1930;
Talbot et al., 1939; Fitch and Bentley,
1949).
Two studies merit special mention for
their relevance to current research. The
first by Tansley and Adamson (1925) was
part of a long term observational and experimental study of the vegetation of the
English chalk. Exclosure experiments
yielded new dominant plants. In their
words (pp. 205-206): ". . . the two interlocked factors, viz. absence of grazing and
consequent increase of competition leading to the success of the taller growing
plants, appear to be far the most potent
influences in changing the vegetation."
Tansley was one of the leading Clementian
successionists. To him competition was the
driving force leading to the local climax
vegetation. Predation was termed the
"biotic factor" and was viewed as a force
that deflected or prevented formation of
climax vegetation. In this light, Tansley
and Adamson's study was theoretically motivated, with the theory being tested by experiments.
I have summarized Tansley and Adamson's results with regard to species diversity as they discussed them but failed to
present in graphical form (Fig. 5). The
curve has a familiar form (e.g., Paine,
Tansley and Adamson 1925
J. Ecology pp. 205-6
; Many
: None
No
Rabbits
Many
Rabbits
Too Many
Rabbits
FIG. 5. Graphical representation of Tansley and
Adamson's (1925) observations on the relation of
plant species diversity to grazing by rabbits.
1977; Lubchenco, 1978), and needs no
further comment other than to emphasize
that the authors' explanation of their results would be well received today.
The second paper, titled "Pattern and
process in the plant community," was A. S.
Watt's (1947) presidential address to the
British Ecological Society. This paper is a
thoroughly modern statement of the ways
physical disturbances like wind erosion,
herbivory, and competition between plants
interact to affect distribution and abundance patterns of plants. It was cited by
Krebs in his influential text (1972) but not
by most ecologists working on similar
problems today (e.g., Levin and Paine,
1974; Platt, 1975; McNaughton, 1979; but
see Connell, 1978; Bormann and Likens,
1979).
Watt (1923) first studied regeneration of
beech woods, doing experiments and describing vegetational changes. Twentyfour years later he had done similar work
in a variety of plant communities and was
ready to make general pronouncements.
He was much less interested in succession
than when he started. Rather he viewed
plant communities as a mosaic of various
dominant associations pock-marked by disturbance-generated patches in varying
states of recovery. Watt understood why
the same association does not always become reestablished in the same place after
a disturbance, i.e., the effects of history or
898
JEREMY B. C. JACKSON
so-called multiple stable points (Sutherland, 1974). He was also a student of morphology and growth patterns, which he
used to explain the comparative competitive success of different species.
Watt had great influence. Some of the
finest derivative work was that of Gillham
(1953, 1955) and Goodman and Gillham
(1954) on the effects of wind erosion, grazing, and sea bird dung on the vegetation
of the Pembrokeshire Islands. These authors did experiments on grazing effects
and observed blowouts of the dense vegetation mats exposed to severe winds.
Speaking of winds and grazing, Goodman
and Gillham (1954, p. 313) state:
Ecologists like Tansley, Watt, and Elton
were interested in immediate causes of distribution and abundance patterns. Some
species of plants propagated vegetatively,
others only by seeds. These differences affected their colonization and competitive
abilities and thus affected distributions.
That was simply the way it was.
For all their splendid work there was little interest in the origin of life history patterns by plant or animal ecologists before
the 1950s. One striking exception was E.
J. Salisbury's (1929) "The biological equipment of species in relation to competition"
to which I have referred previously. This
is a truly extraordinary paper and yet it
has been almost entirely forgotten. Below
These two factors have a strong influ- I list only the life history topics discussed
ence on the competitive powers of a in this paper:
species and hence are to a great extent
indirectly responsible for its abundance
1. Sexual versus asexual reproduction
in a particular place. Thus the domiand its relation to dispersal and comnance of Armeria maritima over Festuca
petitive ability.
rubra on the spray-washed cliff-tops is
2. Parent-offspring conflict and sibling
largely the result of the inability of the
rivalry in plants.
latter to compete under the handicap of
3. Dispersal by fragmentation.
heavy grazing.
4. Morphological variation in stolon
lengths relative to rates of vegetative
Note especially that they viewed competidispersal,
competitive ability, and lotion and predation to be interrelated faccation
of
new
habitats. This was studtors. Predation acted to change the comied
experimentally.
petitive dominant, not to eliminate the
5. Tradeoffs in above-ground versus beimportance of competition. The new domlow-ground stolon propagation.
inant was simply more resistant to the preAbove-ground growth was faster but
vailing conditions of herbivory. Unlike
bore
greater risks of stolons being eatsome ecologists today (Connell, 1975,
en or burned; below-ground growth
1978, 1979, 1980), Gillham, Watt, and
was slower but safer.
Tansley would not have thought to argue
6.
Production of litter, e.g., leaves that do
about the relative importance of competinot easily rot, to make the soil envition and predation. Both were important
ronment unfavorable to other plants.
most of the time, and they had the exper7.
Production of far more seeds than
iments to prove it.
could ever survive to decrease chances
of competitors' seeds surviving.
LIFE HISTORIES AND EVOLUTION:
8. Length of life and why it varies.
T H E NEW PERSPECTIVE
9. Relationship of fecundity to survivorReading all these earlier papers made
ship. Salisbury's admittedly qualitative
me wonder whether the Volterra-Gause
understanding of reproductive value
niche theory had contributed anything
just predates Fisher's (1930) formal
fundamentally new to ecologists' ideas
treatment.
about interspecific competition besides the
10.
Mast years.
mathematics. I believe the answer is yes,
11.
Simultaneous
versus continuous versus
but not for reasons usually claimed. Very
discontinuous germination.
simply, niche theory forced ecologists to
deal with evolutionary arguments.
Salisbury ends with a Harperesque appeal
899
INTERSPECIFIC COMPETITION
for numbers on all the above parameters
and good statistics.
Salisbury's paper was his presidential address to the British Ecological Society,
hardly an obscure offering, yet it has been
, lost from even the botanical literature except for citation by Watt in 1947. Why was
it lost? I believe the explanation is simple.
Poor Salisbury was so far ahead of other
ecologists in his understanding of natural
selection that they simply were not interested. Ecologists had long had a difficult
time with evolutionary thinking. Elton's
chapter on evolution in his brilliant 1927
book is rampantly group selectionist, and
he questioned the application of natural
selection to many ecological problems. His
1929 paper on copepods, which helped inspire Hutchinson's (1951) strongly evolutionary "Copepodology for the ornithologist," is a distribution and abundance
paper lacking in evolutionary argument.
Even so, it too was forgotten.
We have already seen that Lack's (1944)
change of heart about competition was primarily stimulated by Huxley (1942) and
the modern synthesis and only secondarily
by Gause. For most ecologists the modern
synthesis was essential for development of
ideas of life histories, and even afterwards
progress was slow. Cole's paper was not
until 1954, and r- and K-selection and the
flood of interest in life histories not until
the 1960s. Only with understanding of
how phenomena such as character displacement and niche diversification might
occur were ecologists to become comfortable with evolutionary thinking. Thus by
injecting evolutionary perspective, niche
theory profoundly influenced ecology despite the fact that most of its basic tenets
had been developed decades before.
ACKNOWLEDGMENTS
I dedicate this paper to my father Mel
who taught me to suspect the arrogance of
the present. The ideas for this paper germinated in a seminar on the history of
ecology with D. J. Haraway, C. Limoges,
and their students, who patiently tolerated
the rantings of a scientist. N. Knowlton
and L. W. Buss listened bravely to each
new discovery of old ideas and helped
shape the story. J. C. Seidensticker introduced me to the early applied ecology of
the American West. Most of the research
was done in the superb Kline Science Library of Yale University. This study was
partly supported by National Science
Foundation Grant OCE 78-19674.
REFERENCES
Bormann, F. H. and G. E. Likens. 1979. Pattern and
process in a forested ecosystem. Springer-Verlag,
New York.
Bramble, W. C. and M. K. Goddard. 1942. Effect of
animal coaction and seed bed condition on regeneration of pitch pine in the barrens of central
Pennsylvania. Ecology 23:330-335.
Brian, M. V. 1952. The structure of a dense natural
ant population. J. Animal Ecol. 21:12—24.
Cameron, E. 1935. A study of the natural control of
ragwort (Senecio jacobaea L.).J. Ecol. 23:265-322.
Chapman, H. H. 1945. The effect of overhead shade
on the survival of loblolly pine seedlings. Ecology
26:274-282.
Clements, F. E. and J. E. Weaver. 1924. Experimental vegetation. Carnegie Inst. Wash. Publ. 355.
Clements, F. E., J. E. Weaver, and H. C. Hanson.
1929. Plant competition. Carnegie Inst. Wash.
Publ. 398.
Cole, L. C. 1954. The population consequences of
life history phenomena. Quart. Rev. Biol.
29:103-137.
Colwell, R. and E. Fuentes. 1975. Experimental
studies of the niche. An. Rev. Ecol. Syst. 6:281—
310.
Connell, J. H. 1974. Field experiments in marine
ecology. In R. Mariscal (ed.), Experimental marine
biology, pp. 21-54. Academic Press, New York.
Connell, J. H. 1975. Some mechanisms producing
structure in natural communities: A model and
evidence from field experiments. In M. L. Cody
and J. M. Diamond (eds.), Ecology and evolution
of communities, pp. 460—490. Harvard University
Press, Cambridge, Massachusetts.
Connell, J. H. 1978. Diversity in tropical rain forests
and coral reefs. Science 199:1302-1310.
Connell, J. H. 1979. Tropical rain forests and coral
reefs as open nonequilibrium systems. In R. M.
Anderson, L. R. Taylor, and B. Turner (eds.),
Population dynamics, pp. 141-163. Symp. Brit.
Ecol. Soc, Blackwells, Oxford.
Connell, J. H. 1980. Diversity and the coevolution
of competitors, or the ghost of competition past.
Oikos 35:131-138.
Diamond, J. M. 1978. Niche shifts and the rediscovery of interspecific competition. Why did field
biologists so long overlook the widespread evidence for interspecific competition that had already impressed Darwin? Amer. Sci. 66:322331.
Daubenmire, R. F. 1940. Exclosure technique in
ecology. Ecology 21:514-515.
900
JEREMY B. C.JACKSON
of certain deciduous tree seedlings in different
Ellison, L. and W. R. Houston. 1958. Production and
forest sites. Ecology 12:259-298.
herbaceous vegetation in openings and under
canopies of western aspen. Ecology 39:337-345. Hope-Simpson, J. F. 1941. Studies of the vegetation
of the English chalk. VIII. A second survey of
Elton, C. 1927. Animal ecology. Sidgwick and Jackson,
the chalk grasslands of the South Downs. J. Ecol.
London.
29:217-267.
Elton, C. 1929. The ecological relationships of certain freshwater copepods.J. Ecol. 17:383-391.
Hutchinson, G. E. 1940. Book review. Ecology
21:267-268.
Elton, C. 1946. Competition and the structure of
ecological communities. J. Animal Ecol. 15:54- Hutchinson, G. E. 1941. Ecological aspects of succes68.
sion in natural populations. Amer. Natur.
75:406-418.
Elton, C. S. and R. S. Miller. 1954. The ecological
survey of animal communities: With a practical Hutchinson, G. E. 1944. Limnological studies in
system of classifying habitats by structural charConnecticut. VII. A critical examination of the
acters. J. Ecol. 42:460-496.
supposed relationship between phytoplankton
peridocity and chemical changes in lake waters.
Fabricus, L. 1927. Der Einfluss des WurzelwettbewEcology 25:3-26.
erbs des Schirmstandes auf die Entwicklung des
Jungwuchses. Forstw. Centralbl. 49:329-345.
Hutchinson, G. E. 1951. Copepodology for the orFarrow, E. P. 1916. Factors relating to the relative
nithologist. Ecology 32:571-577.
distributions of Calluna heath and grass-heath in Hutchinson, G. E. 1958. Concluding remarks. Cold
Breckland. J. Ecol. 4:57-64.
Spring Harbor Symp. Quant. Biol. 22:415-427.
Farrow, E. P. 1917. On the ecology of the vegetation Hutchinson, G. E. 1959. Homage to Santa Rosalia
of Breckland. III. General effects of rabbits on
or why are there so many kinds of animals?
the vegetation. J. Ecol. 5:1-18.
Amer. Natur. 93:145-159.
Farrow, E. P. 1925. On the ecology of the vegetation Hutchinson, G. E. 1961. The paradox of the plankof Breckland. VIII. Views relating to the probton. Amer. Natur. 95:137-146.
able former distribution of Calluna heath in En- Hutchinson, G. E. 1975. Variations on a theme by
gland. J. Ecol. 13:121-137.
Robert MacArthur. In M. L. Cody and J. M. Diamond (eds.), Ecology and evolution of communities,
Farrow, E. P. 1941. Notes on vegetation changes in
Cavenham Heath, Breckland, J. Ecol. 29:215pp. 492-521. Harvard University Press, Cambridge, Massachusetts.
216.
Fisher, R. A. 1930. The genetical theory of natural Hutchinson, G. E. 1978. An introduction to population
ecology. Yale University Press, New Haven, Conselection. Clarendon, Oxford.
necticut.
Fitch, H. S. and J. R. Bentley. 1949. Use of California annual-plant forage by range rodents. Ecol- Huxley, J. S. 1942. Evolution: The modern synthesis.
Harper Brothers, New York.
ogy 30:306-321.
Fricke, K. 1904. Licht und Schattenholzarten: ein Korstian, C. F. and T. S. Coile. 1938. Plant competition in forest stands. Duke Univ. School Forwissenschaftlich nicht begrundetes Dogma. Cenestry Bull. 3:1-125.
tralbl. f. d. gesamte gesamte. Fortwesen 30:315Krebs, C. J. 1972. Ecology. The experimental analysis of
325.
distribution and abundance. Harper and Row, New
Cause, G. F. 1934. The struggle for existence. Williams
York.
and Wilkins, Baltimore.
Gillham, M. E. 1953. An ecological account of the Lack, D. 1933. Habitat selection in birds with special
reference to the effects of afforestation on the
vegetation of Grassholm Island, Pembrokeshire.
Breckland avifauna. J. Animal Ecol. 2:239-262.
J. Ecol. 41:84-99.
Gillham, M. E. 1955. Ecology of the Pembrokeshire Lack, D. 1940. Habitat selection and speciation in
birds. Brit. Birds 34:80-84.
Islands. III. The effect of grazing on the vegeLack, D. 1944. Ecological aspects of species-formatation. J. Ecol. 43:172-206.
tion in passerine birds. Ibis 86:260-286.
Gimingham, C. H. 1949. The effects of grazing on
the balance between Erica cinerea L. and Calluna Lack, D. 1945. The ecology of closely related species
with special reference to cormorant (Phalacrocorvulgaris (L.) Hull, in upland heath, and their
ax carbo) and shag (P. anstotelis). J. Animal Ecol.
morphological responses. J. Ecol. 37:100-119.
14:12-16.
Godwin, H. 1941. Studies on the ecology of Wicken
Fen. IV. Crop-taking experiments. J. Ecol. Lack, D. 1946. Competition for food by birds of
prey. J. Animal Ecol. 15:123-129.
29:83-106.
Goodman, G. T. and M. E. Gillham. 1954. Ecology Lack, D. 1947. Darwin'sfinches.Cambridge University Press, Cambridge.
of the Pembrokeshire Islands. II. Skokholm, enLack, D. 1954. The natural regulation of animal numvironment and vegetation. J. Ecol. 42:296-327.
bers. Oxford University Press, Oxford.
Harley, J. L. 1939. The early growth of beech seedlings under natural and experimental conditions. Levin, S. A. and R. T. Paine. 1974. Disturbance,
patch formation, and community structure. Proc.
J. Ecol. 27:384-400.
Nat. Acad. Sci. U.S.A. 71:2744-2747.
Heck, K. L., Jr. 1980. Competitive exclusion or comLubchenco, J. 1978. Plant species diversity in a mapetitive delusion. Paleobiology 6:241-242.
rine intertidal community: Importance of herHolch, A. E. 1931. Development of roots and shoots
INTERSPECIFIC COMPETITION
901
Salisbury, E. J. 1929. The biological equipment of
species in relation to competition. J. Ecol.
17:197-222.
Sanders, H. L. 1968. Marine benthic diversity: A
comparative study. Amer. N'atur. 2:243-282.
Shirley, H. L. 1945. Reproduction of upland conifers in the lake states as affected by root competition and light. Amer. Midi. Natur. 33:537612.
Strong, D. R., Jr. 1979. Book review. J. Biogeogr.
6:201-204.
Summerhayes, V. S. 1941. The effect of voles (Microtus agrestis) on vegetation. J. Ecol. 29:14-48.
Sutherland, J. P. 1974. Multiple stable points in natural communities. Amer. Natur. 108:859-873.
fiths (eds.), Serengeti, Dynamics of an ecosystem, pp.
46-81. University of Chicago Press, Chicago.
Talbot, M. W., H. H. Biswell, and A. L. Hormay.
McVean, D. N. 1956. Ecology of Almts glutinosa (L.)
1939. Fluctuations in the annual vegetation of
Gaertn. III. Seedling establishment. J. Ecol.
California. Ecology 20:394-402.
44:195-218.
Tansley, A. G. 1914. Presidential address. J. Ecol.
2:194-202.
Moore, B. 1929. Root competition versus light under
forests. Ecology 10:268.
Tansley, A. G. 1917. On competition between GaNedrow, W. W. 1937. Studies on the ecology of
lium saxitale L. (G. hercynium Weig.) and Galium
roots. Ecology 18:27-52.
s\heslre Pall. (G. asperum Schreb.) on different
types of soil. J. Ecol. 5:173-179.
Paine, R. T. 1974. Intertidal community structure.
Experimental studies on the relationship be- Tansley, A. G. and R. S. Adamson. 1925. Studies on
tween a dominant competitor and its principal
the vegetation of the English chalk. III. The
predator. Oecologia (Bed.) 15:93-120.
chalk grasslands of the Hampshire-Sussex border. J. Ecol. 13:177-223.
Paine, R. T. 1977. Controlled manipulations in the
marine intertidal zone, and their contributions Taylor, W. P. 1930. Methods of determining rodent
pressure on the range. Ecology 11:523-542.
to ecological theory. In C. E. Goulden (ed.),
Changing scenes in natural sciences, 1776-1976, pp. Tourney, J. W. 1928. Foundations of silviculture upon
245-270. Spec. Publ. 12 Acad. Nat. Sci. Philaan ecological basis. John Wiley, New York.
delphia.
Tourney, J. W. and R. Keinholz. 1931. Trenched
plots under forest canopies. Yale Univ. School
Phillips, J. F. V. 1928. The behavior of Acacia meForestry Bull. No. 30.
lanoxylon R. Br. ("Tasmanian Blackwood") in the
Knysna forests: An ecological study. Trans. Roy. Watt, A. S. 1923. On the ecology of British beechwoods with special reference to their regeneraSoc. S. Africa 16:31-43.
tion. J. Ecol. 11:1-48.
Platt, W. J. 1975. The colonization and formation of
equilibrium plant species associations on badger Watt, A. S. 1934. The vegetation of the Chiltern
Hills, with special reference to the beechwoods
disturbances in a tall-grass prairie. Ecol. Monogr.
and their serai relationships. J. Ecol. 22:44545:285-305.
507.
Rayner, M. C. 1921. The ecology of Calluna vulgans.
Watt, A. S. 1947. Pattern and process in the plant
II. The calcifuge habit J. Ecol. 9:60-74.
community. J. Ecol. 35:1-22.
Robertson, J. H. 1947. Responses of range grasses
to different intensities of competition with sage- Watt, A. S. 1957. The effect of excluding rabbits
brush (Artemisia tridentata Nutt.). Ecology 28:1from grassland B (Mesobrometum) in Breckland.
J. Ecol. 45:861-878.
16.
Salisbury, E J. 1920. The significance of the calci- Watt, A. S. and C. K. Fraser. 1933. Tree roots and
the field layer. J. Ecol. 21:404-414.
colous habit. J. Ecol. 8:202-215.
bivore food preference and algal competitive
abilities. Amer. Natur. 112:23-39.
Lutz, H. J. 1945. Vegetation on a trenched plot
twenty-one years after establishment. Ecology
26:200-202.
MacArthur, R. H. 1958. Population ecology of some
warblers of northeastern coniferous forests.
Ecology 39:599-619.
Marsden-Jones, E. M. and W. B. Turrill. 1930. Report on the transplant experiments of the British
Ecological Society at Potterne, Wilts. J. Ecol.
18:352-378.
McNaughton, S. J. 1979. Grassland-herbivore dynamics. In A. R. E. Sinclair and M. Norton-Grif-