ECOSYSTEM THEORY 261
One of the definitions in Webster’s Unabridged Dictionary
seems especially appropriate for the closing decades of the 20th
century, namely, “ the totality or pattern of relations between
organisms and their environment. ” In the long run the best defi-
nition for a broad subject field is probably the shortest and least
technical one, as for example, “environmental biology.”
To understand the scope and relevance of ecology, the
subject must be considered in relation to other branches of
biology and to “ ologies ” in general. In the present age of
specialization in human endeavors, the inevitable connec-
tions between different fields are often obscured by the large
masses of knowledge with the fields (and sometimes also,
it must be admitted, by stereotyped college courses). At
the other extreme, almost any field of learning may be so
broadly defined as to take in an enormous range of subject
material. Therefore, recognized “fields” need to have recog-
nized bounds, even if these bounds are somewhat arbitrary
and subject to shifting from time to time. A shift in scope has
been especially noteworthy in the case of ecology as gen-
eral public awareness of the subject has increased. To many,
“ecology” now stands for “the totality of man and environ-
ment.” But first let us examine the more traditional academic
position of ecology in the family of sciences.
For the moment, let us look at the divisions of biology,
“the science of life.” Morphology, physiology, genetics, ecol-
ogy, evolution, molecular biology, and developmental biol-
ogy are examples of such divisions. We may also divide the
subject into what may be called “taxonomic” divisions, which
deal with the morphology, physiology, ecology, etc., of spe-
cific kinds of organisms. Zoology, botany, and bacteriology,
are large divisions of this type, and phycology, protozo-ology,
mycology, entomology, ornithology, etc., are divisions deal-
ing with more limited groups of organisms. Thus ecology is a
basic division of biology and, as such, as also an integral part
of any and all of the taxonomic divisions. Both approaches are
profitable. It is often very productive to restrict work to cer-
tain taxonomic groups, because different kinds of organisms
require different methods of study (one cannot study eagles by
the same methods used to study bacteria) and because some
groups of organisms are economically or otherwise much
more important or interesting to man than others. Ultimately,
however, unifying principles must be delimited and tested if
the subject field is to qualify as “basic.”
Perhaps the best way to delimit modern ecology is to
consider it in terms of the concept of levels of organization
visualized as a sort of “biological spectrum.” Community,
population, organization, organ cell, and gene are widely
used terms for several major biotic levels.
Interaction with the physical environment (energy and
matter) at each level producing characteristic functional
systems. By a system we mean just what Webster’s College
Dictionary defines as “regularly interacting and interde-
pendent components forming a unified whole.” Systems
containing living components (biological systems or biosys-
tems) may be conceived at any level in the hierarchy. For
example, we might consider not only gene systems, organ
systems, and so on, but also host-parasite systems as inter-
mediate levels between population and community.HISTORICAL REVIEW OF THE ECOSYSTEM
CONCEPTAlthough the term ecosystem was first proposed by the
British ecologist, A.G. Tansley in 1935, the concept is by no
means so recent. Allusions to the idea of the unity of organ-
isms and environment (as well as the oneness of man and
nature) can be found as far back in written history as one
might care to look, and such an idea has been a basic part
of many religions (less so in Christian religions as recently
pointed out by historian Lynn White, 1967). Anthropologists
and geographers have long been concerned with the impact
of man on his environment and early debated the question: To
what extent has man’s continuing trouble with deteriorated
environments stemmed from the fact that human culture
tends to develop independently of the natural environment?
The Vermont prophet George Perkins Marsh wrote a classic
treatise on this theme in 1864. He analyzed the causes of the
decline of ancient civilizations and forecast a similar doom
for modern ones unless “man takes what we would call today
an ecosystematic” view of man and nature. In the late 1800s
biologists began to write essays on the unity of nature, inter-
esting enough in a parallel manner in German, English, and
Russian languages. Thus Karl Möbius in 1877 wrote about
the community of organisms in an oyster reef as a “biocoe-
nosis,” while in 1887 the American S. A. Forbes wrote his
classic essay on “The Lake as a Microcosm.” The Russian
pioneering ecologist V. V. Dokuchaev (1846–1903) and his
disciple G. F. Morozov (who specialized in forest ecology)
placed great emphasis on the concept of “biocoenosis,”
a term later expanded to geobiocoenosis (or biogeocoenosis)
(see Sukachev, 1944), which can be considered a synonym
of the word “ecosystem.”
No one has expressed the relevance of the ecosystem
concept to man better than Aldo Leopold in his essays on
the land ethic. In 1933 he wrote: “Christianity tries to inte-
grate the individual to society, Democracy to integrate social
organization to the individuals. There is yet no ethic dealing
with man’s relation to the land” ... which is “still strictly
economic entailing privileges but not obligations.” Thus,
man is continually striving, with but partial success so far,
to establish ethical relationships between man and man, man
and government, and, now, man and environment. Without
the latter what little progress has been made with the other
two ethics will surely be lost. In the context of the 1970
scene Garrett Harden (1968) says it in another way when he
points out that technology alone will not solve the popula-
tion and pollution dilemmas; ethical and legal constraints are
also necessary. Environmental science is now being called
upon to help determine a realistic level of human popula-
tion density and rate of use of resources and power that are
optimum in terms of the quality of human life, in order that
“societal feedback” can be applied before there are serious
overshoots. This requires diligent study of ecosystems, and,
ultimately, a judgment on the carrying capacity of the bio-
sphere. If studies of natural populations have any bearing
on the problem, we can be quite certain that the optimum
density in terms of the individual’s options for liberty andC005_003_r03.indd 261C005_003_r03.indd 261 11/18/2005 10:21:02 AM11/18/2005 10:21:02 AM