COMMENTARY
What Is Insect Ecology? A Commentary
Robert N. Coulson and
D. A. Crossley, Jr.
T
HE subject
insect ecology is
common in the curricula of departments of entomology in universities throughout North America. This fact
suggests to us that it is a topic generally recognized to be of fundamental significance,
ranking in importance with basic knowledge in insect systematics, morphology,
physiology, and evolution. Principles of insect ecology are the foundation of many of
the basic, applied, and service courses traditionally associated with entomology. However, there is little consensus among insect
ecologists as to the bounds, scope, and
perhaps, aim of the subject. For this reason
numerous approaches are used in teaching
insect ecology, and the subject matter varies
greatly.
Recently we have discussed with colleagues the justification for a course in insect ecology. Attempts to define insect
ecology have led to discussions about the
significance of entomology as a discipline
and about the nature of ecology itself. Presented here are some of our conclusions
about tl1e purpose of insect ecology and its
proper place within the entomology curriculum. Both entomology and ecology are dynamic sciences, and we do not represent
our conclusions as absolute. We offer this
commentary with the intent of presenting
our views on the nature of insect ecology
and to provoke further discussion. Our goal
is to examine the concept of insect ecology
and provide a functional definition that includes both the scientific and professional
charges of entomology. The issue that we
address is whether insect ecology embraces
more than an elaboration of basic concepts
of ecology illustrated with examples from
entomology. For reasons outlined below,
we contend that it does. This issue is important because its resolution influences the
Robert N. Coulson is a member of the
Dep. of Entomology, Texas A&M Univ., College Station, Tex.
D. A. Crossley,Jr. is a member of the Dep.
of Entomology, Univ. of Georgia, Athens,
Ga.
64
represents the functional relationship of the
way knowledge is organized and presented
two fields of study.
to students of entomology and ecology.
What is Entomology and What Is Its PurOur approach is to consider the concept
of insect ecology using hierarchical levels of pose? Few would argue that entomology is
organization (Fig. 1). This technique is cer- not the study of insects, but it is not clear
tainly not new. The use of hierarchies, or that all who study insects are therefore enspectra of organization, is a common feature tomologists. Certainly basic research using
of ecology texts (see Odum 1983 for ex- insects as experimental subjects has led to
ample). The use of hierarchy theory in eco- significant developments in various fields
logical interpretation has been examined in within the biological sciences (including
detail by Allen & Starr (1982). For our pur- ecology). However, it appears to us that enposes, we are concerned with the study of a tomology persists as a separate entity within
particular system. Three levels in a hier- biology because it is an applied science, i.e.,
archy are involved: a level of study (the because of the importance of insects in agrisystem), a lower level required for explana- culture, natural resource management,
tion (the subsystem or subsystems), and a public health, and veterinary medicine.
We found support for this contention by
higher level of interpretation (the suprasystem). For example, if we were interested examining the college affiliation of departin studying the southern pine bark beetle ments of entomology within North Amerguild (i.e. a community of scolytid beetles ican universities, t)1Jes of papers published
that inhabits pines), our explanation would by the Entomological Society of America,
and course offerings provided by departcome from examination of the population
dynamics of its members, and our interpre- ments of entomology. Of the 61 departtation would come from examination of the ments of entomology identified, 50 were
effects produced at the forest ecosystem associated with colleges of agriculture or
level.
natural resources. It is also noteworthy that
more than 50% of the scientific papers pubThe concept of insect ecology presented
herein is defined by our selection of the lished by the Entomological Society of
number of levels of integration included, America in the years 1960-86 occurred in
the level of primary focus or study, the the Journal of Economic Entomology.
level(s) used for explanation, and me level About 25% appeared in me Annals of the
used for interpretation. The selection pro- Entomological Society of America, which
cess was tempered by examination of sev- generally deals with issues of basic entomological science. The remaining 25% were
eral seemingly simple, yet fundamentally
published in Environmental Entomolo&.'Y
important, questions. What is entomology
and what is its purpose? What is ecology and (R.N.C., unpublished data). Viewed in the
context of levels of organization (Fig. 1), ca.
what is its purpose? Why study insect
80% of d1e courses offered by departments
ecology?
of entomology occur within four levels:
populations, organisms, organ systems, and
The Questions
organs. This observation can be verified by
Most fledgling students can cite the ety- examining the course listings for departmological origins and dictionary definitions ments of entomology in university cataof the terms entomology (me study of in- logues. The types of courses traditionally
sects) and ecology (the study of me interre- taught in departments of entomology can be
lationships between living organisms and classed into mree general categories. The
their environment). However, textbook au- first category includes core courses dealing
thors usually define the terms in specialized wim basic issues in entomology, such as inways that reflect their own perspective or sect systematics, morphology, physiology,
system of organization. In developing a defi- ecology, etc. The second category deals with
nition it is instructive to examine the terms applied courses, such as integrated pest
in the context of how entomology and management, biological control, toxicology,
ecology are currently practiced and toward etc. The third category deals with service
courses, generally provided to other acawhat objectives. This approach will produce
anomer specialized definition, but one mat demic programs within the university, such
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COMMENTARY
BIOSPHERE
BIOMES
LANDSCAPES
LANDSCAPES
ECOSYSTEMS
ECOSYSTEMS
COMMUNmES
POPULATIONS
ORGANISMS
ORGAN SYSTEMS
ORGANS
TISSUES
CELLS
SUBCELLULAR ORGANELLES
MOLECULES
Fig. 1. Hierarchical spectrum of organization illustrating the levels of integration
associated with entomology, traditional insect ecology, and the proposed concept of
insect ecology. Note that the leve4 Landscape, is normally not included in the spectrum,
but is a central feature of the proposed concept of insect ecology.
as forest entomology, horticultural entomology, veterinary entomology, medical entomology, etc.
Because of the preponderance of departments of entomology in colleges of agriculture (and natural resource management),
the types of papers published by entomologists in their professional journals, and the
nature of course offerings in entomology
departments, we conclude that contemporary entomology is in essence an applied
science. However strictly entomology might
be defined, most contemporary practitioners of entomology are probably professionals in an applied science. Historically,
interest in insects has often accompanied
t11eireconomic importance (see Smith et al.
1973). The purpose of entomology can be
summarized under two headings: effects of
insects on humans, their food, and their environment; and contribution of new knowl-
66
edge about insects to science. These
statements of purpose are not new and represent a viewpoint probably shared by most
entomologists, although some might argue
that d1e ordering of the two purposes is reversed.
What Is Ecology and What Is Its Purpose?
Ecology is a more difficult term to define
than entomology. Current textbooks offer a
rich spectrum of definitions, some narrow
in scope, some broad, and some obscure.
There are numerous reasons for these circumstances, which are addressed by McIntosh (1985) in his thorough and scholarly
treatment of the subject. McIntosh points
out that the most common definition is an
abstract (or embellishment) of the concept
presented by Haeckel (1869), and translated
in Allee et al. (1949): ecology is the study of
the interrelations of plants and animals with
their environments. Examples of definitions
of this genre include Odum's (1983) study
of the totality or pattern of relations between organisms and their environment;
and Ricklefs' (1983) study of plants and animals, both as individuals and together in
populations and biological communities, in
relation to their environments. Although
ecologists do not agree on the optimal definition of the term ecology, most would concede that it includes consideration of at least
the population, community, and ecosystem
levels in the organizational hierarchy.
The discipline
may be diverse, but most
ecological studies have one of two purposes: to explain the abundance and distribution of organisms, or to explain how
ecological systems work. The first purpose
embraces the large variety of research in
population ecology and on natural history of
plants and animals. The second purpose
contains research at the community-ecosystem-landscape levels (i.e., the higher
levels in the hierarchy [Fig. 1]. Like entomology, ecology has application to humans,
their food, and environments. Ecology, however, has remained in essence a basic
science. True, there are applied ecologists,
applied journals, and a section of applied
ecology within the Ecological Society of
America, but the society and its journals remain largely devoted to basic rather than
applied research. It can justifiably be argued
that much ecological research has important
implications for human society, but again,
the purpose of the research is usually scientific understanding.
Why Study Insect Ecology? In the introduction we stated that insect ecology embodied more than an elaboration
of
principles of ecology illustrated with examples from entomology, and that it embraced a distinct viewpoint and represented
a subject of fundamental importance to entomology students. Following is the rationale for this contention.
Insect Diversity, Abundance, and Distribution. No other animal group exhibits the
immense diversity of ecological interactions
found in the Class Insecta. Other groups of
organisms are uniquely adapted to their
ecosystems, and some are economically important, but insects are distinctive in their
variety of trophic interactions, environmental adaptations, niche exploitations, etc.
The ecology of insects is unique from this
aspect. Fortunately, entomologists are comfortable with detail. By and large, students of
BUliETIN OF THE ESA
Fig. 2. A simplified conceptual model of elemental cycling in a terrestrial ecosystem
emphasizing the presence and activities of arthropod consumers. Indirect regulation of
elemental movements by arthropods is indicated by the hourglass-shaped valves on
those flows. Virtually all fluxes within ecosystems are known or believed to respond to
various levels of arthropod activity (after Seastedt & Crossley [1984 J).
entomology
are attracted by the diversity of
insects and become comfortable with the
large variety of interactions. A5 practitioners
in an integrative science, ecologists have as
one of their goals the identification of paradigms that reduce large bodies of information to unifying principles. Entomologists,
we believe, feel less constrained. Combining basic principles with a rich diversity
is a challenge for insect ecology.
Impact on Ecosystems. Activities of insects
influence the major ecological processes of
terrestrial and freshwater ecosystems (Fig.
2). Primary production, consumption, and
decomposition is strongly influenced, if not
controlled or regulated, by activities of
insects. Effects of insects on ecosystem processes influence natural and human-managed ecosystems in ways that we are still
discovering. The importance of insects in
ecosystems is evidenced by the fact that recent texts dealing with insect ecology (Price
1984) and ecological entomology (Huffaker
& Rabb 1984) are introduced by a discussion of basic concepts of ecosystems.
Integration of Basic and Applied Biology.
Because entomology is essentially an applied science and ecology a basic one, combination of the two sciences permits a
unique synthesis of ecological background
SUMMER 1987
and applied
interpretation.
We do not dis-
pute the value of coursework in general
ecology or in other specialized sub-areas
(plant ecology, for example), but we think
that the basic/applied synthesis is of unique
value. In many instances students entering
an entomology program have weak backgrounds in ecology or do not recognize the
relevance of principles of ecology to various
entomological pursuits. Because of the diversity of insect/environment interactions, a
course in insect ecology permits presentation, illustration, and discussion of an array
of pertinent ecological principles without
overwhelming students with management
implications. Other disciplines in applied
plant and animal science have the same
dilemma in structuring coursework for
ecological background and applied interpretation but lack adequate diversity to develop broad-based ecological discussion.
Insect Ecology Defined
With the preceding discussion on definition, purpose, and scope of entomology and
ecology as background, we can now consider a definition of insect ecology. In the
introduction we stated the definition would
be developed from a consideration of the
levels of organization involved (Fig. 1), and
that both the scientific and professional
charges of entomology should be addressed. We offer our working definition:
insect ecology is the study of the interactions
and influences of insect populations and
communities on ecosystem processes that
affect landscape structure, function, and
change. Following is the rationale for this
definition.
Levels of Organization. As stated previously, in the study of a system there are
three important hierarchical levels: the
system (level of study), the subsystem (level
used for explanation), and the suprasystem
(level used for interpretation). In our definition of insect ecology the level of focus or
study is the ecosystem, the levels of explanation include insect populations and insect
communities, and the level of interpretation
is the landscape (Fig. 1 and 3). In particular,
we are interested in how insect populations
and communities influence and interact
with basic ecosystem processes (primary
production, consumption, and decomposition) to affect landscape structure, function,
and change.
Insect ecologists
who have struggled
to
apply the ecosystem concept in heterogeneous environments will welcome the development of an emphasis on landscape
ecology (Naveh & Leibermann
1983,
Forman & Godron 1986). "Landscape" has
been included as a distinct entity in our organizational hierarchy. Most representations
of the levels in the spectrum do not recognize landscape as a category (i.e., the progression is from ecosystem to biome).
However, we found little evidence of
biome-level interpretation of ecosystem
processes. We believe that much of integrated pest management and natural resource management, for example, is based
on ecosystem concept but is actually practiced at the level of the landscape (i.e., the
interpretation of outcome of management
practices is directed at the landscape level).
A landscape is defined as a heterogeneous
land area composed of a cluster of interacting ecosystems that are repeated in similar form throughout. Landscapes vary in
size, down to a few kilometers in diameter
(Forman & Godron 1986). By this definition
it is clear that the federal agencies responsible for various types of land management
(e.g., the USDA Forest Service) are actually
dealing with landscapes comprising mul-
67
COMMENTARY
LANDSCAPES
EFFEcrs
ON LANDSCAPE
STRUcruRE, FUNCTION.
AND
LEVEL
CHANGE
OF INTERPRETATION
ECOSYSTEMS
IN'ffiRA.cnONSA.'ID
INFLUENCES ON
ECOSYSTIiM PROCESSES
LEVEL OF STIJDY
POPULATIONS
INSiCTS
COMMUNITIES
•••••.
INSECTS
IN COMMUNITIES
PUNTS
LEVEL
OF EXPU\NAll0N
Fig. 3. The levels of organization and
their interrelationships for the proposed
concept of insect ecology. The level of
focus or study is the ecosystem, the levels
used for explanation are insect populations and communities, and the level used
for interpretation is the landscape. Insect
populations and communities influence
and interact with ecosystem processes,
which affects landscape structure, function, and change.
tiple interacting ecosystems. This statement
is true also for a farmer managing a farm.
The landscape concept is also helpful in
dealing with the inherent fuzziness.~ssociated with time and space resolution in the
definition of ecosystem.
The integration of the various hierarchical
levels in the context of an insect ecology
problem can be illustrated by considering
an outbreak of bark beetles in a pine forest.
The pine forest is one element (ecosystem)
in a landscape that may include other forest
types: lakes, streams, pasture, etc. Various
biotic and abiotic factors influence the population dynamics of the bark beetles (or in
some cases the guild or community
dynamics of bark beetles). Occasionally, epizootic population levels occur that result in
excessive levels of consumption,
which in
turn reduce primary production within the
pine forest ecosystem. The impact of the
event influences landscape structure (the
distribution
of energy,
materials,
and
species in relation to the sizes,. shapes,
numbers, kinds, and configurations of landscape elements
or ecosystems),
function
(the flows of energy, materials, and species
among the component ecosystems), and dynamics (alteration in the structure ane! function of the ecological mosaic over time). In
this example we have shown that population
and community
dynamics influence ecosystem processes
to affect a landscape.
While the insect ecologist could be interested in the basic ecological issues involved
in the interaction described, the entomologist might be more concerned with the effects produced
by the interactions
(forest
management implications).
Relation to Traditional
View of Insect
Ecology. The traditional or common focus
of insect ecology generally includes levels
dealing with organisms,
populations,
and
communities
(see the chapter headings in
Price [1984] (Fig. 1). In our concept of insect
ecology we have not emphasized behavior
of individual organisms. This subject is certainly important and is treated in numerous
courses offered in an entomology
curriculum. It has been covered in detail in Huffaker & Rabb (1984). We assume
that
students taking a course in insect ecology
have a background
that includes course
work dealing with the natural history of insects. However, basic principles of population dynamics (the study of the causes for
change in the distribution and abundance of
insects through space and time) and community dynamics
(studies
dealing with
issues associated
with commonness
and
rarity of species assemblages)
are central
components
in our organizational
scheme.
Although the ecosystem is recognized as an
important element of insect ecology in both
of the contemporary
texts (Price 1984, Huffaker & Rabb 1984), the mechanisms
that
link the lower levels to the ecosystem are
not discussed in detail. Interpretation of the
influences and interactions of insect populations and communities
on ecosystem processes in relation to effects at the landscape
level is the unique aspect of our proposed
concept
of insect ecology.
One consequence of the concept presented here is that
an insect ecologist must have broad training
in an unusually large number of levels in
the organizational hierarchy.
Conclusion
We have offered a synopsis of our conclusions about the nature of insect ecology. The
discussion was based on an examination of
the definition, scope, and purpose of entomology and ecology. A definition of insect
ecology was proposed and cast within the
framework of hierarchical levels of organi-
zation: the study of the interactions
and
influences of insect populations
and communities on ecosystem processes that affect
landscape structure, function, and change.
In this concept of insect ecology, the level of
focus is the ecosystem, the levels of explanation are insect populations and insect communities, and the level of interpretation
is
the landscape. This definition represents insect ecology as a unique subject for coursework and includes consideration of both the
scientific and professional charges of entomology. We anticipate disagreement among
entomologists
and ecologists with the concept of insect ecology presented here and
we welcome dialogue.
Acknowledgment
We are indebted to and acknowledge the contributions of students and faculty in the Department of Entomology and Institute of Ecology at
the Univ. of Georgia who helped in formulating
our concept of insect ecology and provided criticism of early versions of the manuscript. We acknowledge and thank W.J. Mattson (USDA Forest
Service) and F. P. Hain (North Carolina State
Univ.) for their reviews of this paper. We thank S.
Spalding (Univ. of Georgia) and A. M. Bunting and
L. Gattis (Texas A&M Univ.) for providing technical assistance. This paper is TA No. 22063 of the
Texas Agric. Exp. Sm.
References
Cited
Allee, W. c., A. E. Emerson, O. Park, T. Park &
K. P. Schmidt. 1949. Principles of animal
ecology. Saunders, Philadelphia.
Allen, T. F. H. & T. Starr. 1982. Hierarchy: perspectives for ecological complexity. Univ. of
Chicago.
Forman, R. T. T. & M. Godron. 1986. Landscape
ecology. Wiley, New York.
Haeckel, E. 1869. Entwicklungsgand und aufgaben der zoologie. Jenaische Ztschr. 5:353.
Huffaker, C. B. & R. L. Rabb. 1984. Ecological entomology. Wiley, New York.
Naveh, Z. & A. S. Lieberman. 1983. Landscape
ecology: theory and application. Springer, New
York.
McIntosh, R. P_1985. The background of ecology:
concept and theory. Cambridge Univ., New
York.
Odum, E. P. 1983. Basic ecology. Saunders, Philadelphia.
Price, P. W. 1984. Insect ecology. Wiley, New
York.
Ricklefs, R. E. 1983. The economy of nature.
Chiron, New York.
Seastedt, T. R. & D. A. Crossley, Jr. 1984. The in·
fluence of arthropods on ecosystems. BioScience 34:157-161.
Smith, R. F., T. E. Mittler & C. N. Smith [eds.].
1973. History of entomology. Anou. Rev., Palo
Alto, Calif.
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