ent during the time when the present magnetization in the same direction as ple of such a pathway. In the nonliving
magnetization was acquired. Apparently, the lava. If the second hypothesis were part of the ecosystem, circulation of
the best procedure is to continue to ac- true, this would not always occur. energy and matter is completed by such
cumulate field evidence. The results that very recent flows are physical processes as evaporation and
It was possible (2) last summer to always found to be normally magnetized precipitation, erosion and deposition. The
make a survey of the remanent magnet- and baked clays have the same magnet- ecologist, then, is primarily concerned
ization of some of the lava flows of the ization as the lava which bakes them with the quantities of matter and energy
San Francisco Mountain, Verde Valley, are in accord with evidence from other that pass through a given ecosystem and
and Mormon Mountain volcanic fields lava series. It must be concluded that with the rates at which they do so. Of
in northern Arizona. It was thought suffi- this evidence from northern Arizona almost equal importance, however, are
cient to determine the polarity rather lends support to the first hypothesis. If the kinds of organisms that are present in
than the exact direction of magnetiza- this hypothesis is correct, the earlier flows any particular ecosystem and the roles
tion of the specimens. For this it is pos- in this region must be at least about 1 that they occupy in its structure and or-
sible in the majority of cases to use a million years old (7). ganization. Thus, both quantitative and
Brunton compass. Assuming that the N. D. OPDYKE qualitative aspects need to be considered
specimen is magnetized normally or re- S. K. RUNCORN in the description and comparison of eco-
versely, the poles of the specimen are Museum of Northern Arizona, Flagstaff, systems.
brought near the poles of the compass, and Department of Geodesy and Ecosystems are further characterized by
and repulsion or attraction is noted. In- Geophysics, Cambridge University, a multiplicity of regulatory mechanisms,
creased sensitivity can be obtained by Cambridge, England which, in limiting the numbers of organ-
moving a pole of the specimen from isms present and in influencing their
side to side over one end of the com- References and Notes
physiology and behavior, control the
Downloaded from www.sciencemag.org on December 12, 2011
pass needle and noting whether the 1. Advances in Phys. 4, 191 (1955). quantities and rates of movement of both
needle moves in phase or antiphase with 2. We are indebted to the Geological Society of matter and energy. Processes of growth
America and the Museum of Northern Arizona
the specimen. for grants and to H. S. Colton, director of the and reproduction, agencies of mortality
Occasionally, a few specimens in a Museum of Northern Arizona, for his help and (physical as well as biological), patterns
interest.
single flow were found to be magnetized 3. H. S. Colton, Museum Northern Arizona Bul. of immigration and emigration, and hab-
differently from the rest, but, as these No. 10 (1950). its of adaptive significance are among
4. R. P. Sharp, J. Geol. 50, 481 (1942).
specimens were usually very intensely 5. H. H. Robinson, U.S. Geol. Survey Profess. the more important groups of regulatory
magnetized and had been collected from Paper No. 76 (1913). mechanisms. In the absence of such
exposed points, it was assumed that 6. 0. E. Childs, Bull. Geol. Soc. Amer. 59, 353 mechanisms, no ecosystem could continue
(1948).
lightning strokes were responsible. 7. Details of these investigations are being incor- to persist and maintain its identity.
From the extent of the erosion of the porated in a report that is in preparation. The assemblage of plants and animals
lava tops and fronts, Colton (3) has ar- 1 February 1956 visualized by Tansley as an integral part
ranged the lavas of the San Francisco of the ecosystem usually consists of nu-
volcanic field in order of age, stage I merous species, each represented by a
being the oldest, stage V the youngest. population of individual organisms. How-
Sharp (4) considers stage III lavas to Ecosystem as the Basic ever, each population can be regarded as
be younger than about 60,000 years and Unit in Ecology an entity in its own right, interacting
stage II lavas probably older. Robinson with its environment (which may include
(5) considers the earliest flows in this The term ecosystem was proposed by other organisms as well as physical fea-
region to be Pliocene. Work done by Tansley (1) as a name for the interaction tures of the habitat) to form a system of
Childs (6) on pediplane surfaces of the system comprising living things together lower rank that likewise involves the dis-
Colorado plateau shows that the stage I with their nonliving habitat. Tansley re- tribution of matter and energy. In turn,
flows rest on a late Pliocene surface and garded the ecosystem as including "not each individual animal or plant, together
that the stage II flows occurred before only the organism-complex, but also the with its particular microenvironment,
the first glaciation in the San Francisco whole complex of physical factors form- constitutes a system of still lower rank.
peaks, probably in the early Pleistocene. ing what we call the environment." He Or we may wish to take a world view of
Nine stage III flows, one stage IV, and thus applied the term specifically to that life and look upon the biosphere with its
one stage V flow were examined and level of biological organization repre- total environment as a gigantic ecosys-
found to be normally magnetized. This sented by such units as the community tem. Regardless of the level on which
is in accord with the evidence from the and the biome. I here suggest that it is life is examined, the ecosystem concept
New England varved clays which cover logically appropriate and desirable to can appropriately be applied. The eco-
a fair proportion of this time. The data extend the application of the concept and system thus stands as a basic unit of ecol-
from Iceland and France would indicate the term to include organization levels ogy, a unit that is as important to this
that stage II covers the Pliocene-Pleisto- other than that of the community. field of natural science as the species is
cene boundary. One out of six lavas ex- In its fundamental aspects, an ecosys- to taxonomy and systematics. In any
amined in the Verde Valley volcanic tem involves the circulation, transforma- given case, the particular level on which
field was reversely magnetized, and 13 tion, and accumulation of energy and the ecosystem is being studied can be
out of 21 in the Mormon Lake volcanic matter through the medium of living specified with a qualifying adjective-for
field were reversely magnetized. things and their activities. Photosynthesis, example, community ecosystem, popula-
All these flows were of stage I or II. decomposition, herbivory, predation, tion ecosystem, and so forth.
In these fields, one normally magnetized parasitism, and other symbiotic activities All ranks of ecosystems are open sys-
lava and two reversely magnetized flows are among the principal biological proc- tems, not closed ones. Energy and matter
have been found overlying baked clay esses responsible for the transport and continually escape from them in the
horizons. The latter were found to be storage of materials and energy, and the course of the processes of life, and they
magnetized concordantly with the re- interactions of the organisms engaged in must be replaced if the system is to con-
spective lavas. The clay was thus heated these activities provide the pathways of tinue to function. The pathways of loss
by the lava and, on cooling, acquired a distribution. The food-chain is an exam- and replacement of matter and energy
22 JUNE 1956 1127
frequently connect one ecosystem with Table 1. Temperatures for 11 dogs during hypothermia experiments.
another, and therefore it is often difficult
to determine the limits of a given ecosys-
tem. This has led some ecologists to re-
ject the ecosystem concept as unrealistic
and of little use in description or analy-
sis. One is reminded, however, of the fact
that it isalso difficult, if not impossible,
to delimit a species from its ancestral or
derivative species or from both; yet this
does not destroy the value of the concept.
The ecosystem concept may indeed be
more useful when it is employed in rela-
tion to the community than to the popula-
tion or individual, for its limits may be
more easily determined on that level.
Nevertheless, its application to all levels
seems fully justified.
The concept of the ecosystem has been
described under many names, among
them those of microcosm (2), naturkom-
plex (3), holocoen (4) and biosystem tion of the organism to the stress of the
Downloaded from www.sciencemag.org on December 12, 2011
(5). Tansley's term seems most success- shock of surface cold application (3).
fully to convey its meaning and has in Cooling the body from the outside re-
fact been accepted by a large number of quires a long time to extract the body
present-day ecologists. I hope that it will heat through the outer layers of fat and
eventually be adopted universally and muscular natural insulation (1, 4).. It
that its application will be expanded be- seemed to us that a more rapid lowering
yond its original use to include other of the body temperature could be ac-
levels of biological organization. Recogni- complished by internal cooling through
tion of the ecosystem as the basic unit in the lowering of the temperature of the
ecology would be helpful in focussing at- animal's circulating blood in an external
tention upon the truly fundamental as- heat exchanger. The cooled blood return-
pects of this rapidly developing science. ing to the body would act as a heat-ab-
FRANCIS C. EVANS sorbing and transferring medium to re-
Institute of Human Biology, duce rapidly the body temperature.
University of Michigan, Ann Arbor To accomplish this, the following pro-
References
cedure is used. After minimal anesthesia
with intravenous Nembutal and with
1. A. G. Tansley, Ecology 16, 296 (1935). tracheal intubation, the animal is con-
2. S. A. Forbes, Bull. Peoria Sci. Assoc. (1887).
3. E. Markus, Sitzber. Naturforsch. Ges. Univ. nected to a respirator. The carotid ar-
Tartu 32, 79 (1926). tery is cannulated with a polyethylene
4. K. Friederichs, Die Grundfragen und Gesetz- tube that is threaded through a circulat-
massigkeiten der land-und forstwirtschaftlichen Fig. 1. Cardiographs of dog: (1) normal
Zoologie. (Parey, Berlin, 1930). ing pump and is then coiled around a sinus rhythm, prehypothermia; (2, 3, 4)
5. K. Thienemann, Arch. Hydrobiol. 35, 267 spindle that is immersed in a refriger- increasing R-R internal and prophasive
(1939).
ated alcohol-water bath. The return end delay in repolarization of myocardium,
30 January 1956 of the polyethylene tube is then inserted shown by markedly prolonged electric
in the femoral vein. systole, (5) apparent cardiac asystole;
In a series of 30 dogs, very good re- (6) sinus rhythm, early posthypothermia.
sults have been obtained. A dog is cooled
Hypothermia by Internal Cooling from 100°F to 80°F in 20 minutes. No
cardiac fibrillation, shivering, or shock
Mammals normally maintain their manifestations are encountered during
body temperatures at a constant and rela- the procedure. Several animals have been
tively high level. Chemical and other cooled to a complete cardiac standstill
1--
body reactions speed up with increase in and then returned to normal rate and
I
temperature and slow down at lower rhythm by rewarming (Fig. 1). It is nec- z
temperatures. Chemical-reaction rates essary only to bring the dog up to 900F, Lx
cr.
approximately double for each 20-deg which is above the shivering point. The
rise in temperature. animal recovers to normal by itself after
I
In surgery it is desirable to slow down this. Lu
W.
body reactions to allow more time for Rewarming is accomplished by the use
certain operations (1, 2). Hypothermia of a heating unit in the cooling bath. The 3:
has been used with some success in such refrigeration is shut off, and the heating ROOM TEMP 72 °
work, but the cooling methods that were
used introduced several problems, such
unit is activated to warm gradually the
bath, which in turn warms the circulating :;P
i
55 BATH 410
-
°
w
as ventricular fibrillation, the necessity of blood of the animal (Table 1). 20 40 60 80 100 120
MINUTES
prolonged preoperative preparation of By this method of producing hypo-
the patient, and, most important of all, thermia by internal heat exchange, the Fig. 2. Related temperatures during hy-
the biological catastrophe of overreac- blood and body temperatures may be pothermia.
1128 SCIENCE, VOL. 123