AMER. ZOOL., 19:1173-1175(1979).
Concluding Remarks
O. J. REICHMAN
Museum of Northern Arizona, Flagstaff, Arizona 86001
Even though competition between close- each other that they employ similar means
ly related taxa is not completely known, to resolve their competition. For example,
the increasing interest in competition be- Galapagos finches seem to have become retween more distantly related organisms source specialists primarily on the basis of
made this symposium timely for several bill morphology. When competitors are
reasons. First, it is hoped that the discussion more distantly related they arrive in the
and publication of the symposium topics competitive arena through convergence on
will stimulate ecologists to look for competi- a common resource and are frequently extion between distantly related taxa in the tremely different from each other in most
systems they are studying. During attempts ways other than the use of that resource.
to locate participants with actual data on Thus, each taxon could be playing the
competition between distantly related evolutionary game with different rules and
species, numerous investigators stated that equipment, making it difficult for either to
they thought they might have anecdotal in- effectively counter the other. For example,
in the system discussed by Brown et al., the
formation but not hard data.
Another reason for the symposium is that ant colonies can shut down the production
diffuse competition may be widespread and of workers during times of low resource
fairly important in structuring some com- availability, thereby reducing the amount
munities, as the papers on marine bottom of biomass that must be supported. Alcommunities suggest. Indeed, to the ma- though rodents can use torpor or curtail
rine ecologists, the topic on the symposium reproduction, they cannot go to the exis somewhat of a ho-hum issue. Jeremy tremes of the ant colonies and reduce their
Jackson has pointed out that he sometimes size or eliminate a limb to reduce their endeals with seven phyla of competitors in one ergy requirements.
location.
One of the major distinctions that came
A final reason for the symposium is that out of this symposium was between those
investigations into competition between organisms that compete for space and are
distantly related taxa may yield insight into essentially sessile and those that compete
basic competitive interactions which are for a biotic resource and are primarily
obscured by the traditional approach of mobile. The marine system of bottom dwelcomparing a few functional differences lers tends to be representative of the former
{e.g., bill length or foraging height in trees) and as such is similar to terrestrial plant
between closely related species. Considera- systems. Indeed, the terms used by Woodin
tion of basic competitive interactions leads and Jackson for growth forms have their
to the main question of this symposium: analogs in terminology of terrestrial plant
Are the pressures leading to and alleviating communities. Although this marine system
competition between distantly related taxa has some depth component, it is essentially
different in kind and quantity from those two dimensional and as such space itself
between more closely related species?
provides fewer dimensions on which potenOne- of- the- basic differences- between- tial- eompetitors-ean-speeializer-One- mightcompetition involving closely related spe- expect a high degree of convergence in
cies and that involving distantly related taxa these systems as selection pressures on a
arises directly from the differences in their wide variety of organisms are focused on
phylogenetic proximity. Closely related means to commandeer space. Within the
competitors are usually similar enough to ocean bottom communities the resources
1173
1174
O.J. REICHMAN
are relatively small, unidirectional, and uniform, and the organisms must secure a
patch of the bottom in order to obtain the
use of the non-exclusive resources (e.g.,
sunlight, plankton, detritus). In terrestrial
systems, animals may defend space (i.e.,
home ranges or territories), the the space is
only a way of maintaining exclusive control
of a resource.
The competition that goes on in systems
where the participants are attempting to
gain space would put a premium on adaptive colonization schemes and on ways of
avoiding predators. The colonizing tactics
used by the competitors would be important as they jockeyed for the appropriation
of any available space. In the sessile bottom
communities the animals are relatively easy
prey for predators. This should put pressure on the members of the community to
evolve distinct predator avoidance characteristics so as not to be a part of a group of
animals with similar predator escape mechanisms on which a generalized predator
could specialize. Again, terrestrial plant
communities exhibit similar patterns.
Where competition is for a more biotic
resource (e.g., food) the nature of the variability of the resource would play an important role. In systems such as those discussed
by Smith and Balda, and Brown et al., the
resource is highly variable in time and/or
space. This variability, coupled with the typical variability in the size and shape of a
resource, provides numerous dimensions
along which competitors can specialize.
Competitors in these systems, by being
grossly different, can escape the stresses of
a variable resource in many different ways,
thus leading to a high diversity of competitors on a resource, including both
closely and distantly related taxa. The competitors in the above system compete in
ecological time, responding to resource variability, and measures of their ongoing
competition perhaps can be made experimentally.
Where resources are more stable temporally the competitors tend to have resolved their competition evolutionarily and
we see them, at this time, as having very
little overlap in resource utilization. This
evolutionary character displacement is well
illustrated in the papers by Fleming and
Wright, and the hummingbird studies of
Kodric-Brown and Brown, and Carpenter.
The three-dimensional open ocean system discussed by Hayward and McGowan is
substantially different from those discussed
above. The authors have studied an incredibly diverse community whose specific
components are highly predictable. The
structure, however, is virtually unfathomable for two reasons. One involves the difficulties of sampling in the open ocean on a
small enough scale to investigate spatial
phenomena (even though their several
cubic meter samples are extremely small for
their system). A cause of greater concern is
that the currents are stronger than the
swimming capabilities of the organisms and
introduce a strong stochastic component to
the arrangement of the community. Thus,
the organisms and their competitive interactions have only a slight influence on
the structuring of the community.
The systems involving human influence
offer a chance to investigate recent, ongoing, competitive processes. Ron Carroll
presented evidence of multi-faceted, diffuse competition in a agro-ecosystem and
Kraemer explored the complex interactions that can occur with the introduction of
exotic species.
Insights such as those offered by Levins
should stimulate theoretical investigations
into the basic nature of competition, including competition between distantly related
taxa. It will be important to know if we can
drape the ideas of competition between distantly related species on the same framework as that used for other considerations
of competition.
I doubt if any of the participants in the
symposium would consider competition the
only, or even the major, factor structuring
all communities. The papers presented
herein show a wide range in both the
influence of competition in structuring
communities and the difficulties in measuring that influence. Certainly there can be
many arguments about the points presented in the concluding remarks, and I am
sure each participant would have his or her
own specific comments and complaints.
Nevertheless, the ideas about differences
between space and food competitors, and
the ideas concerning the stability of biotic
CONCLUDING REMARKS
1175
resources, might serve as useful working and by the Ecology Division of the ASZ.
hypotheses which can be tested with theory, Special thanks are due to Mary Wiley for
observation, and experimentation.
her incredible efficiency and pleasant manFunding for this symposium was pro- ner. Many individuals contributed to the
vided by a National Science Foundation ideas leading to the symposium and special
grant to the American Society of Zoologists, thanks go to Jim Brown and Chris Smith.