Download Competition and macroevolution: the ghost of

Biological journal of the Linnean Socicp (1993), 49: 87-98
Competition and macroevolution: the ghost of
competition yet to come?
JUDITH C. MASTERS, F.L.S.*
Population Genetics Laboratory, Museum of Comparative ,Zoology, Haruard Uniuersip,
Cambridge, M A 02138, U . S . A .
AND
RICHARD J. RAYNER, F.L.S.?
Bernard Price Institute for Palaeonlological Research, University of the Witwatersrand,
Private Bag 3, W i t s 2050, South Africa
Received I0 December 1991, accepted for publication 3 March 1992
Competition theory is the focus of much debate among both neontologists and palaeontologists. This
paper explores the expansion of competition theory into macroevolution, since this is the relevant
context for palaeobiologists, and challenges the contention that microevolutionary processes are
generally inappropriate to the interpretation of macroevolutionary pattern. We show that the term
‘interspecific competition’ is imprecise, since it conflates processes operating at various hierarchical
levels, and recommend a terminological change in accordance with hierarchy theory. Finally, we
reassess the rBle of competition and its absence in radiations. Since evolutionary novelties must be
fixed at speciation, and speciation occurs in response to habitat destruction rather than the freeing of
ecological space, we believe the r6le of competition to be minimal in both radiation and the
generation of novelty.
ADDITIONAL KEY WORDS:-Evolutionary
- speciation.
novelties - hierarchy - microevolution - radiation
CONTENTS
Introduction . . . . . . . . . . .
Microevolutionary concepts in macroevolution
. .
Competition, mass extinctions and radiations . . .
Species, speciation and the origin of evolutionary novelties
Conclusions . . . . . . . . . . .
Acknowledgements . . . . . . . . .
References . . . . . . . . . . .
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INTRODUCTION
Some years ago, Benton (1987) published an extensive critique of the r6le of
competition in macroevolutionary theory. His researches led him to two main
*Present address: Department of Zoology, University of the Witwatersrand, Private Bag 3, Wits 2050, South
Africa.
?Author to whom correspondence should be addressed.
87
0 1993 The Linnean Society of London
0024-4066/93/050087 12 $08.00/0
+
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J. C. MASTERS AND R. J. RAYNER
conclusions: first, that the fossil record does not provide evidence of evolutionary
progress, or improvement in competitive abilities, through time; second, that
competition is often wrongly invoked to explain large-scale patterns in the fossil
record. In illustration of the latter, he demonstrated that many purported cases
of competitive displacement and replacement involving animal taxa can be
linked to mass extinction events. Benton’s argument echoes sentiments expressed
by Emiliani (1982) on reviewing turnovers among marine protistan species. In
Emiliani’s analysis, replacement in this group has followed rather than preceded
extinction, making competition an unlikely cause of the latter.
Within a neo-Darwinian context, where competition has traditionally
provided one of the major forces for change, Benton’s views may be regarded as
radical. Nevertheless, they have received little in the way of challenge or
refutation in the literature. Rather, his paper has been cited as a recent reference
point for evolutionary thinking (Connell, 1988; Aronson, 1989; Hofman, 1989;
Jablonski, 1989, 1991; Knoll, 1989; Turkington, 1989; Baur & Baur, 1990).
Hence, it appears that, although there may be some detractors (e.g. Vermeij,
1973, 1977, 1987; Jackson, 1988; Thayer, 1988; Rosenzweig & McCord, 1991),
Benton’s approach is reasonably well accepted within the evolutionary
community.
We profess ourselves to be as conformist as the above-mentioned majority. We
have recently reviewed the major floral and faunal replacements that
characterize the South African fossil record, and believe that competition is
unlikely to have played a major rBle in these events (Rayner & Masters, in
press). However, lest readers grow uneasy at the suggestion of consensus in
palaeobiology, there are two important facets of Benton’s argument with which
we disagree strongly. These are: the rhle of competition in radiations following
upon the heels of mass extinctions; and Benton’s general contention that ‘. . . the
concepts of microevolution, including intra- and interspecific competition, may
be wholly inappropriate to macroevolution’ (p. 329). We shall discuss the latter
issue first.
MICROEVOLUTIONARY CONCEPTS IN MACROEVOLUTION
Underlying Benton’s depreciation of competition in macroevolution is a
principle that there ‘are ‘problems of scaling’ in applying ‘[microevolutionary]
concepts such as competition, adaptation and selection pressure to large-scale
and long-term aspects of evolution’ (Benton, 1987: 331). This assumption is not
valid. Twenty years ago, Lewontin indicated how selection could operate at all
levels of biological organization: ‘the generality of the principles of natural
selection means that any entities in nature that have variation, reproduction,
and heritability may evolve’ (Lewontin, 1970: 1).
More recently, Vrba & Gould (1986: 225) have claimed that hierarchy is a
property of nature, and that:
‘A general theory of biology is a theory of biological levels-of how they arise
and interact. Entities that play the same role in the evolutionary process
must be classed together . . . The same principle also applies to evolutionary
processes themselves. The same general causes are likely to operate at each
level, both in its initial evolution, and subsequently in the de novo
COMPETITION AND MACROEVOLUTION
89
introduction and sorting of variation. We must consider the evolutionary
process itself as basic, and explore its common modes of action u p and down
the hierarchy-particularly interactions between levels . . .’
Thus, if competition is indeed found to be inappropriate to macroevolution, it
must be for reasons more explicit than the general difficulty of transferring
processes across levels. In fact, a sound argument could be made that
‘interspecific competition’ is already a macroevolutionary concept, if
macroevolution is understood to include patterns and processes pertaining to
groups or clades at or above the species level (e.g. Hallam, 1989). An obsession
with species identity (‘us’ vs ‘them’) rather than with the nature of the processes
in operation, has led to an ecological terminology that is at odds with hierarchy
theory, and confusing. For instance, when we talk about ‘interspecific
competition’, we could mean any one of the following scenarios:
(a) all interaction involves characters emergent at the organism level;
members of species A and species B have equivalent abilities to acquire the same
resources, but the environment has a limited carrying capacity; because of
circumstances unrelated to competitive ability or fitness discrepancies (e.g. a
difference in the initial frequencies of the two species), after a passage of time all
of the organisms in a particular area are representatives of one species;
(b) all interaction involves characters emergent at the organism level;
members of species A are more efficient at acquiring the same resources as are
sought by members of species B, and the carrying capacity of the environment is
limited; the presence of species A organisms has a direct effect on the fitness of
organisms of species B; after a passage of time all of the organisms in a particular
area are representatives of species A;
(c) interactions involve groups of two or more organisms-e.g.
breeding
partners, colonies, troops, herds or populations; for reasons unrelated to
competitive ability (e.g. the group became established first, and now accounts
for a significant proportion of the environmental carrying capacity) , after a
passage of time all of the organisms in a particular area are representatives of a
single species;
(d) interactions involve groups of two or more organisms, and organized
group activity enables more effective control of resources than the organisms
would be capable of individually; the fitness of other groups is directly affected
by the activities of the focal group, and after a period of time all the organisms in
a particular area are members of a single species;
(e) true interspecific competition, i.e. interaction involves characters
emergent at the species level; species A competes as a unit with species B.
Alexander & Borgia’s ( 1978: 456) interpretation of interspecific competition is
along these lines: ‘Units or groups such as species, then, may be established
through individual or genic selection, yet persist or fail as a result of competition
with other species-hence, through a kind of group selection’.
If we disregard sources of selection other than competition for the moment,
then according to the scheme of Vrba & Gould (1986), scenario (a) represents
sorting at the organismal level which, through upward causation, results in
sorting at the level of species. Scenario (b) represents competition and selection
at the organismal level, which also causes sorting at the species level. Because of
the similarity in their higher level effects, these two scenarios may be difficult to
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J . C. MASTERS AND R. J. RAYNER
distinguish by observation. However, an explication of the forces potentially
operating, and of the level of their operation, opens this problem to experimental
investigation.
Scenarios (c) and (d) refer to interactions at the group level, e.g. between two
colonies of eusocial hymenopterans. Scenario (c) describes a sorting process,
while scenario (d) depicts competitive selection at this level. I n both cases,
downward causation will result in sorting at the organismal and genic levels,
while upward causation will effect sorting at the level of the species or
community.
We encountered difficulties in envisaging how scenario (e) might operate in
nature [unless the species comprises only one population, in which case it
becomes synonymous with scenario (d)]. The only character that appears to be
emergent at the species level or above, is geographic distribution Uablonski,
1986). Can this be identified in any meaningful way with a resource which might
generate competition? Can species compete for distributions in some way that is
not simply the sum of all interactions between organisms and/or infra-specific
groups for access to a particular region of the habitat?
Several authors (Hull, 1980; Damuth, 1985; Eldredge, 1985, 1986; Tattersall,
1989) have argued that the highest hierarchical level at which entities can
function as ecological interactors is the population. Damuth ( 1985) coined the
term ‘avatar’ to describe representative populations of a single species in different
ecological communities. Eldredge ( 1985, 1986) omitted the species level entirely
from his economic or ecological hierarchy, which he used to portray the levels of
matter-energy transfer, stating unambiguously that: ‘In a purely ecological,
economic, energetics sense, species do not exist’ (1985: 159).
The problem of identifying coherent economic rBles is exacerbated for entities
above the species level. Benton (1991: 100) has touched on this difficulty by
questioning whether key adaptations can confer advantage at such levels: ‘Do
families and orders possess monolithic adaptations that can be compared at clade
level, or do all individuals in a clade have an equivalent advantage over all (or
most) individuals in another?’
If we accept that the highest level of competitive interaction is the population
or avatar, does this mean that competition is irrelevant to evolution at higher
levels? Indeed not. Vrba’s (1980) Effect Hypothesis is an example of processes
occurring at the organismal level which sort upwardly to produce highly
significant macroevolutionary patterns. Therefore, microevolutionary processes
are potentially important to macroevolutionary pattern-although not in the
form of simple extrapolation, as has been the wont of palaeontologists in the
past-and Benton’s (1987) attempt to isolate microevolutionary processes from
macroevolution is ill-advised,
Jackson (1988: 31 l ) , who is a firm believer in the importance of lower level
competitive effects for macroevolution, expressed his dissatisfaction with the
relationship between ecology and macroevolution as follows:
‘The basic intellectual problem is that we lack a clear theory and mechanism
to translate ecological interactions into macroevolutionary trends, and
understanding needs coherent theory’.
We suggest that evolutionary ecologists begin by overhauling their ‘intra-’ and
‘interspecific’ terminology, and bring it into line with hierarchical thinking.
COMPETITION AND MACROEVOLUTION
91
Processes under consideration must be described in terms of their hierarchical
level of operation, and of the units involved. This means that ambiguous terms
like ‘interspecific competition’ must be dropped unless species level processes are
particularly being invoked, in favour of ‘interorganismal’ or ‘interavatar’
nomenclature. Only then will clear theorising be possible.
COMPETITION, MASS EXTINCTIONS AND RADIATIONS
Benton’s (1987) re-interpretation of pattern and process in the fossil record
dealt a telling blow against theories invoking competition as the major force in
extinctions. However, he did not entirely rule out a rble for competition in
macroevolution: ‘Competition may be involved in the subsequent radiation of
the replacing group [once the original inhabitants have gone extinct]: [the
replacing group] could have a key adaptation that enables it to resist extinction,
or which assists the adaptive radiation into empty ecospace’ (1987: 331).
What exactly is the rble for competition that Benton envisages in making this
statement? Certainly, as he is well aware, the survival of a lineage during a mass
extinction or subsequent radiation on account of a particular adaptation or
exaptation, need not call for a ‘competitive’ explanation; neither scenario need
involve interaction with other organisms. Walter (1988), in his critique of the
competitive exclusion principle, identified the rble generally assigned to
competition during radiations as one of absence: competition prevents
radiations; absence of competition permits radiations. That this is a position that
is commonly espoused, is supported by a glance at the literature:
‘The same sort of diversification [adaptive radiation] follows . . . when a
group spreads to a new and, for it, ecologically open territory’ (Simpson,
1953: 223).
‘[Extinction] is, in one sense, the enabling force of the biosphere. Since most
species are extraordinarily resistent to major evolutionary change and since
many habitats are fairly full of species, how could evolution proceed if
extinction did not open space for novelty?’ (Gould, 1982: 12).
‘The more common pattern implies that established groups preempt
resources, and that their extinction releases rapid adaptive radiation and
morphological evolution in groups that had previously been less diverse . . .’
(Futuyma, 1986: 359).
‘Rebound intervals provide settings of unbridled radiation in which
innovations can be captured and new adaptive zones occupied in relative
freedom from pre-emptive competition that typifies clade interactions during
background times’ Uablonski, 1989: 364).
Similar positions have been taken by Stebbins (1966), Sepkoski (1985) and
Hallam ( 1989).
Because of their devastating effects on faunas and floras, mass extinctions are
viewed as being particularly important in this context: they are major clearers of
ecological space.
‘In the absence of mass extinction, . . . macroevolution would be confined to
the slow process of anagenesis and evolutionary novelties would appear
J. C. MASTERS AND R. J. RAYNER
92
rarely at best . . . only mass extinction would break this stagnation by
clearing ecospace for the radiation of new lineages’ (Sepkoski, 1985:230).
‘Mass extinctions can break the hegemony of species-rich, well-adapted
clades and thereby permit radiation of taxa that had previously been minor
faunal elements’ Uablonski, 1989:357).
Some authors propose a more active rBle for this absentee competition than
simply ‘permitting’ radiation:
‘. . . species radiate rapidly when a breakthrough into new empty adaptive
zones is achieved [Simpson, 1944, 1953;Newell, 1952;Mayr, 1963;Walker
& Valentine, 19841 . . . The emphasis shifts to the exploitation of new
habitats as the cause of major ‘‘advances” in evolution (e.g. lungs, amniotic
egg, endothermy)’ (Benton, 1987: 308-309, our emphasis).
Jablonski (1989:363) writes of faunal turnovers which were mediated by mass
extinctions. Sepkoski (1985:225) states that ‘mass extinctions , . , promote rapid
cladogenesis following the removal of established lineages’. Knoll ( 1989: 285),
citing the work of Sepkoski, suggests that: ‘It has been proposed that mass
extinction is a major force in the generation of evolutionary novelty’ (all
emphases ours).
We term this absentee competition ‘the ghost of competition yet to come’. And
this ghost disturbs us, as do several of the utterances quoted above. Mass
extinction is a pattern, the definition of which is still somewhat contentious. It
cannot be regarded as a process, a mediator, a promoter, or a force in any true
sense. Furthermore, cladogenesis, at the level of speciation, has certainly
occurred in the absence of mass extinction. T o view all change in the absence of
mass extinction as anagenetic is clearly wrong.
Our purpose in quoting these statements is not to devalue the opinions of their
authors or portray their interpretations as idiosyncratic, but to highlight a
fundamental contradiction in the Modern Synthesis with regard to the rBle of
natural selection in the generation of diversity. Exploring the Modern Synthesis
further, we find that it is not only the absence of competition that drives
diversity, but the absence of any form of natural selection whatsoever. Huxley
( 1942: 323-324),in formalizing neo-Darwinism, stated:
‘Decreased selection-pressure permits radiation. This is true not only for
species or subspecies but for entire groups. In the former case the result is
higher variability, in the latter more extensive evolutionary divergence and
radiation . . , The principle can be generalized in relation to competitorpressure as well as predator-pressure’.
Further:
‘. . . divergence is normally slow, but occasionally, as on oceanic islands and
other places where the intensity of selection is relaxed, it may be much more
rapid and more extensive than usual’ (p. 383).
In his paradigmatic study of the diversification of the Galapagos geospizids,
Lack (1940:326) identified the three main causal factors as: ‘(1) The almost
complete absence of food competitors . . . (2)The almost complete absence of
COMPETITION AND MACROEVOLUTION
93
predators’ which ‘[bloth must diminish the intensity of selection’ and (3) the
opportunities for geographic isolation.
This attitude does not square with other tenets of the Modern Synthesis, e.g.
‘. . . There is operative a selection-pressure forcing life to occupy every
geographical area and every ecological niche within the area’ (Huxley, 1942:
387-388).
If natural selection is a major force driving evolutionary change, why do
radiations depend on its absence? Just what is the rBle of natural selection in
speciation and the generation of evolutionary novelty? We believe that these two
processes are intimately connected, because, along with Mayr (1963: 1 l ) , we
hold that ‘[tlhe origin of new species, signifying the origin of essentially
irreversible discontinuities with entirely new potentialities, is the most important
single event in evolution’. Any evolutionary novelty must become fixed initially
in a speciation event. Reasons for this have been clearly explicated by Futuyma
(1987), who pointed out that, because of the mobile and transitory nature of
local populations, any novelties that arise in the absence of speciation are likely
to be lost. Hence, an understanding of the evolutionary processes producing such
novelties must take into account the conditions necessary for speciation.
Although Jackson (1988: 31 1 ) is no doubt correct in suggesting that ‘speciation
remains as much a black box as ever’, our ignorance is not total, and it behoves
us to apply what information we have, to lighten our darkness.
SPECIES, SPECIATION AND THE ORIGIN OF EVOLUTIONARY NOVELTIES
As Gould pointed out (1982: 12), ‘most species are extraordinarily resistent to
major evolutionary change’. More than this, organisms avoid the destructive
effects of natural selection whenever possible. Many specific adaptations,.
especially those related to the successful achievement of syngamy, are closely
fitted to the environment in which speciation occurred (Paterson, 1982). A
habitat shift would bring strong selective pressures to bear upon organisms which
were tempted to make such a n injudicious move. Hence, organisms will tend to
remain within their preferred habitats, and geographic distributions of species
will be largely predictable in terms of environmental characteristics, barring the
vagaries of serendipity.
In the event of environmental change, organisms will seek out conditions
similar to those they inhabited previously. Speciation will only occur in ‘trap
situations’ from which emigration is prevented-perhaps
by the surrounding
topography, or by the presence of a hostile environment. Impressive support for
habitat fidelity has been derived from studies of palaeoenvironments and their
associated faunal assemblages in European deposits of Pleistocene age. During
this period, dramatic shifts occurred in the locations of climatic zones within
Europe and Asia, associated with advances and retreats of the Northern
Hemisphere ice sheets. The distributions of fossil species of Coleoptera (Coope,
1975, 1978, 1979) and Mammalia (Kurten, 1968; Butzer, 1972; Stuart, 1974)
have been observed to coincide closely with the ranges of their preferred
biozones. This relationship was consistent even over vast distances: Ullrich &
Coope (1974) quoted one habitat shift of 7000 km, in which the faunal
assemblage remained constant. In all cases, the aspect of the physical
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J. C. MASTERS AND R. J. RAYNER
environment that appeared to exercise the major influence on faunal
distributions was temperature. Coope (1979: 262) interpreted his findings as
follows:
‘Three options are open to species when changing environments become
intolerable: they may adapt to the new conditions, they may become extinct,
or they may move to an area where conditions are still acceptable. Of these
three, the last was the most usual response. As the climate changed rapidly,
the opportunity to “evolve out of trouble” seems to have been beyond their
genetic agility. Rather they simply tracked the tolerable environment across
the continents’.
Similar conclusions have been reached by Cronin (1987) in his studies of
Pleistocene and Holocene marine faunas.
The concept of a preferred species habitat is one well understood by both
neontologists and palaeontologists. T o any field biologist it is a fundamental rule,
and it constitutes the rationale behind studies in palaeoecology, where indicator
species are used to identify the conditions prevailing during particular episodes
in geologic time. Why, then, does the myth persist that empty niches or vacant
adaptive zones are sufficient to cause members of a population to leave the
comfortable world of the specific habitat, and brave the uncharted valleys of the
adaptive landscape in order to climb the peaks of increased fitness?
The myth persists as a legacy of the classical Darwinian ‘struggle for
existence’. In the absence of mass extinctions, competition is so intense that some
organisms are driven to find new habitats, or at least to change their modes of
life. This interpretation has been severely criticised by Wiens (1977), who has
shown that populations normally live well below the carrying capacity of the
environment. Competition is thus an inconsistent and intermittent force which
only occurs at times of particular hardship. During the paradigmatic conditions
of hardship envisaged for speciation, however, Walter, Hulley & Craig (1984)
have estimated that the impact of competition would be weak compared with
the intense selective pressures experienced by a small population under
directional selection in a hostile environment. Further critiques of the r6le of
competition as an explanatory theory for evolutionary change are contained in
Cole ( 1960), Connell ( 1980), Grine ( 1981), Simberloff ( 1982), Salt ( 1984,
selected papers), Arthur (1987), Walter (1988) and Hulley, Walter & Craig
( 1988a, b).
With regard to the interpretation of competition as a force for resource
partitioning and character displacement, we have a further objection to add. It
has never been clear to us how this force is deemed to operate. Under the
circumstances in which competition will be most significant, i.e. times of scarcity,
organisms are known to broaden their tolerances for food (and other habitat
resources), rather than to restrict them further: the hungrier they are, the less
choosy they become (Pyke, Pulliam & Charnov, 1977). Sympatric species will
come to overlap more in their requirements, not less. Thus, when competition
could feasibly have an effect, selection would operate in opposition to it: fussy
eaters are unlikely to survive famines.
Regardless of the effects of competition when present, let us return to the r6le
of absentee competition, or the ghost of competition yet to come. Central to this
discussion is the dialectic between organism and environment described by
COMPETITION AND MACROEVOLUTION
95
Lewontin (1983) and touched on by Benton (1987). Lewontin pointed out that
an environment or niche has no existence without the organism that inhabits it:
in fact, an organism in a very real sense creates the environment it inhabits,
along with its own ecological boundaries. But-and this is crucial-‘[tlhe error is
to suppose that because organisms construct their environments they can
construct them arbitrarily in the manner of a science fiction writer constructing
an imaginary world . . . Where there is strong convergence is in certain
marsupial-placental pairs, and this should be taken as evidence about the nature
of constraints on development and physical relations, rather than as evidence for
pre-existing niches’ (Lewontin 1983: 283). In the same vein, mammals came to
pursue similar life-styles to dinosaurs, not because dinosaurs vacated habitable
ecological spaces, but because of the structural constraints operating on
functional vertebrate bodies.
Mass extinctions and radiations may well be linked in time and space, but this
correlation does not mean one event causes the other. A far more likely
explanation is that the two events share a common cause-i.e. catastrophic
environmental change. Vrba ( 1985) has formalized this as the ‘turnover-pulse
hypothesis’. Such an explanation implies a much looser relationship between
mass extinction and radiation than has been implied previously; radiations may
follow on the heels of mass extinctions, and then again, they may not.
Simpson (1953) has indicated several instances where there is a time lag
between extinction and replacement, which might argue against invoking
common cause as an explanation. O n the other hand, it might simply imply that
stochastic forces play a much larger r6le in speciation and radiation than the
search for repeated patterns might allow.
Since the major selective pressures responsible for evolutionary change are not
ecological space, but habitat destruction, we believe that both the presence and
the absence of other species with similar ecological requirements (e.g. dinosaurs
for mammals) is irrelevant to the generation of novelties.
CONCLUSIONS
Benton (1987) demonstrated that competition was not a significant force in
extinctions. We have extended this insight to argue that competition is also not a
major force in radiations. Is competition theory then completely irrelevant to
any interpretation of macroevolutionary pattern? We believe that competition
can only operate as a selective process at the level of the population or below,
and that any influence it may have on macroevolution must be as a result of
upward sorting from these levels. At present the significance of competition for
microevolution is controversial, and its consequences for macroevolution are far
from obvious. We hope that we have at least clarified the debate, and delineated
the field on which battle should now commence.
Benton (1991) has argued that competition should not be regarded as the
default condition, but that the onus for demonstrating its relevance to
macroevolution be placed squarely on the shoulders of those who support it. We
agree, and suggest that this responsibility be extended to supporters of the ghost
of competition yet to come. But how may such a theory be tested? Using the
insights granted us by hierarchy theory, an obvious starting point is to seek a
microevolutionary analogy for this process. The appropriate analogue appears to
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J. C. MASTERS AND R. J. RAYNER
be ecological succession, in which existing dominants need to be cleared before
propagules from other taxa can flourish. If this is a valid comparison, the
macroevolutionary process it suggests is one in which extant populations are
constantly generating variable daughter ‘propagules’ which are being widely
disseminated to a variety of environments, and dying out. Only during times of
extinction do these propagules have the opportunity to speciate. Is there any
evidence to support such a process?
Furthermore, we must expect the boundaries of species distributions to be
tested constantly if species indeed are constrained to their habitats chiefly by
inter-individual and inter-population competition. A logical consequence of this
is that species’ distributions will interdigitate, and their positions in space will
fluctuate continually, since the interactions maintaining them must be
performed over and over again for each pair of organisms or avatars. Is there
any evidence of this in nature?
Previous studies of competitive exclusion (e.g. Diamond, 1973) have tended to
map the distributions of organisms at too low a level of resolution to establish
whether competitive interactions can indeed be responsible for such patterns.
The necessary data are therefore lacking. We encourage adherents of
competition to incorporate hierarchy theory into their thinking, so that the
appropriate information can be amassed, and competition theory put to the test.
In closing, we wish to remind readers of the teleological underpinnings of
competition theory as espoused by Darwin, and many of his followers
subsequently. In a letter to Asa Gray, Darwin (cited in Eiseley, 1958: 183) made
the following comment: ‘The same spot will support more life if occupied by very
diverse forms . , . And it follows . . . that the varying offspring of each species
will try (only a few will succeed) to seize on as many and as diverse places in the
economy of nature as possible’. Eiseley traced this teleology back to William
Paley, author of Nuturul Theology, in which Paley suggested:
To this great variety in organized life, the Deity has given, or perhaps there
arises out of it, a corresponding variety of animal appetites. For the final
cause of this we have not far to seek. Did all animals covet the same element,
retreat, or food, it is evident how much fewer could be supplied and
accommodated, than what at present live conveniently together, and find a
plentiful subsistence’.
Paley’s belief in providential design was the primary motor for his work.
Darwin, in Eiseley’s analysis, swallowed this teleology as a result of his early
exposure to, and memorization of, Paley’s writings. What’s our excuse?
ACKNOWLEDGEMENTS
This paper grew out of animated discussions with Professors S. J. Gould, R. C.
Lewontin, A. H. Knoll and the members of their laboratories, and we
acknowledge with gratitude the stimulation and hospitality they all afforded us.
We are grateful, too, to the following, who read and commented on an earlier
draft of the manuscript: Michael Benton, James Carpenter, Dennis Cullinane,
Niles Eldredge, Richard Lewontin, James Maki, Colin Patterson, Michael
Rosenzweig. J.C.M. wishes in particular to thank Richard Lewontin and Ruth
Hubbard for providing practical support and encouragement. We acknowledge
COMPETITION AND MACROEVOLUTION
97
the South African F.R.D. and the University of the Witwatersrand for financial
support.
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