plant and animal taxa as soon as possible. Without the observations and experimental results of physiological ecology, we will be hard pressed to predict or ...
commentary WHAT
IS PHYSIOLOGICAL
ECOLOGY?
Introduction C. Richard
Tracy1 and J. Scott Turner1-2
The name "physiological is a hybrid of phys ecology" clearly indicates that this discipline or of physiology iology and ecology. But is physiological ecology simply another dimension ecology alone, or is physiological ecology unique in some fundamental way from its parent "are there any emergent to physiological disciplines (in the jargon of ecology, properties These and other questions were asked of several biologists who were requested ecology?")? to submit short essays outlining their views. We hoped to use these essays to compile (a) definitions of physiological ecology, and (b) opinions on the relationship between physiolog ical ecology and its parent disciplines. Not surprisingly, the opinions were eclectic. They varied all the way from the opinion that "there is (not) a lizard's eyelash of difference between 'physiological
ecology,'
'environmental
physiology,'
'ecophysiology,'
or
'comparative
physi
and environmental ology'" (Bennett), to a jesting comment that physiological ecologists phys iologists can be identified on the basis of their wardrobe (Strain). The lack of unanimity among the essays is perhaps the most striking result of this "exper It suggests that physiological iment" with opinion. has not yet "sorted out" as a ecology it is usually possible to distinguish the bulk Thus, while discipline with distinct boundaries. from most of physiology, it is often more difficult to distinguish of ecology between physio in emphasis appear to logical ecology and environmental physiology, although differences exist (Gates, Heinrich, Huey, Janzen, King, McClure, McNab, Miller, and Strain). Further ob between these subdisciplines is the fact that other areas of science, such scuring distinctions as behavioral ecology and ecological morphology, have developed with intimate connections more than once that physiological Indeed, the opinion was expressed physiological ecology. if it did not deal with behavioral and morphological ecology would be poor science aspects of the questions addressed (see Huey and King). The lack of clear definition may not be troublesome to many, but as knowledge expands, there is a natural tendency to subdivide scientific disciplines and to define sharp boundaries of these new disciplines. This process can have the undesirable effect of isolating scientists into parochial "clubs," and it can have the beneficial effect of allowing scientists to throw off the shackles of "standard methods" and "acceptable that practitioners of an questions" established discipline might define. Sharp definition of the borders of any scientific discipline can also stifle the interchange of ideas that fuels pro in its incipient stages of development often need to gress in science. On the other hand, scientists asking new kinds of questions a problem, without being obliged to conform to standards, develop new ways of approaching from other disciplines, which may be inappropriate. Indeed, some essayists warn that simply to examine questions from comparative in physiological ecol borrowing methods physiology results (see Huey and McClure). Thus it appears that good scientific ogy can yield misleading than those guidelines judgment may be a better guide to the pursuit of knowledge imposed with scientific disciplines. by arbitrary doctrines associated Separate from the philosophical question of the relationship between physiological ecology of our day-to-day and related areas of science are the practical necessities lives as scientists in some classification which force us to engage of our colleagues. For example, we seek out our own we with to with interests similar whom discuss ideas. We also need may colleagues to identify scientists who can evaluate scientific to our professional reports submitted jour to ensure that our journals publish nals. Categorization of scientific material also is necessary for the stated purposes of the journal. For example, physiological material that is appropriate is seen to provide the mechanistic of ecological at higher processes explanations ecology to extinction, levels of integration (e.g., population growth, patterns of mortality, vulnerability nutrient cycling, competitive etc.; see essays by Bartholomew, exclusion, Billings, Chabot, Gates, Heinrich, Huey, Janzen, King, McClure, McNab, Miller, Strain). But must a manuscript
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at a higher level of integration than physiology to be acceptable explicitly address questions material for publication in ESA journals? How do we simultaneously protect authors from area of reviewer prejudices and whimsical opinions not shared by all peers in a developing to journals from research reports that science, at the same time that we protect subscribers diverge a great deal from the stated mission of the journal? A philsophical and importance of phys examination of the position, state of development, cau that cannot be avoided, but it should be approached is an exercise iological ecology of a biological does not affect either the previous or tiously. While classification species can profoundly evolution of that taxon, classification of scientific subsequent disciplines affect the field's course of future development. of ESA should be Thus, the membership in the processes that result in the evolution by these essays to participate challenged (and/ or extinction) of scientific disciplines. of Zoology and Entomology department Colorado State University Fort Collins, Colorado 80523 2Present address: Department of Zoology Duke University Durham, North Carolina 27706
Definitions
and Opinions
A. Bartholomew3
George
is a continuum, but for its study the establishment of subdivisions is an operational Biology on the basis of the fields of scientific nature is not organized necessity. Unfortunately, is apt to be biologically Elaborate partitioning and intellectually unrealistic specialization. Itprobably does more harm than good to distinguish between environmental sterilizing. physi and physiological Each deals with aspects of physi ology, ecological physiology, ecology. ology that are relevant to ecology, and vice versa. Ifone defines ecology as the study of the relations between organisms and environment, relevant physiology covers an ecologically enormous of physiology that affect exchanges between area, including all those aspects or that affect the behavioral interactions between organisms. organism and environment, the biophysical and biochemical attempt to identify and describe Physiological ecologists use in coping with environmental that individual organisms mechanisms factors, or that they in ecological interactions. Such findings establish a framework or mechanism that employ can also be used to analyze and interpret ecological interactions at population and higher levels
of
integration.
The methods it more empirical of physiological tend to make than theoretical. ecology the primary data of physiological are physiological, these data are inter Although ecology is more important preted in the context of ecology. The intent of the physiological ecologist than the methods he uses to gather his data. Ideally, he should be a technically competent and also a good naturalist and an able ecologist. If he has sufficient physiologist insight he can draw ecological inferences from material derived from virtually any physiological disci pline.
of Biology department University of California Los Angeles, California
90024
Albert Bennett4 Ido not believe there is a lizard's eyelash of difference between "physiological ecology," or (these days) "comparative "environmental To physiology," "ecophysiology," physiology." Ihave called my interests all these things and more. I think me, these fields are synonymous: the distinctions among them are contrived and/or trivial. They all represent the same approach to organismal biology. To my mind, physiological involves functional studies that have three character ecology istics: (1) they are highly empirical, function under natural biotic and (2) they emphasize
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and (3) they consistently refer to performance within the context of an abiotic conditions, intact individual organism. The range of possible observations broad: is thus exceptionally from the biochemical level up, is appropriate performance, virtually any aspect of mechanistic our measurements will be indistinguishable and at times necessary. Sometimes from those an histologist, a behaviorist, or a population our in of a systemic physiologist, ecologist; is often different. This breadth and interpretation sometimes terpretive context present prob and we may be told that a particular study is not "ecology" or not lems for other biologists, I regard this type of outlook as largely the problem "behavior" or not "respiratory physiology." of the observer. We cannot really expect everything we do to appeal to all our co-workers; one person's stunning insight is another's turned page. What we should do is to interpret our data in our own context and make explicit the implications of our observations for as many as we find possible. different levels of biological organization 4School of Biological Sciences University of California Irvine, California 92717
W. D. Billings5 as a in isolation, but an integral part of ecology is not a science Physiological ecology if at all, from ecophysiology; It is not clearly distinct, whole. both must deal with problems of in field environments. organisms Iview physiological First, to under ecology as playing at least two major roles in ecology. we must know how the plants, in a changing stand how ecosystems operate biosphere, in that ecosystem should animals, and microorganisms grow and reproduce. Whole ecosystems be studied with regard to gains and losses of populations, soils, nutrients, energy, water, and But if one wants to know what makes an ecosystem tick, some components. atmospheric How do the further dissection is necessary. What are the roles of the physical components? become established, metabolize, grow, and reproduce? component organisms in The second major role of physiological and is ecology helping to explain migrations distributions of taxa. Involved here is research on the physiological, morpho geographical of local populations, and higher genetically ecotypes, logical, and reproductive adaptations and its components. based units in relation to the total environment Biospheric change can often be very fast. It is imperative that we know the potential environmental tolerance ranges of many
plant
and
animal
taxa
as
soon
as
possible.
Without
the observations
and
experimental
to predict or explain migrations, results of physiological ecology, we will be hard pressed are possible and ecosystemic roles of important taxa, if, indeed, such predictions extinctions, at all.
of Botany department Duke University Durham, North Carolina
27706
Brian F. Chabot6 is, as the name implies, a hybrid enterprise. This is its strength. Any ecology Physiological a in ecology construct which distinguishes this from other approaches to definition attempt are indistinct The boundaries between most related disciplines is likely to be self-defeating. and should be left so. In the end, it is the biological itself, and its attendant phenomenon, that justify the research effort and the spectrum of approaches used. There is hypotheses little added virtue in identifying the question as lying within the realm of physiological ecology or any other discipline. are usually interested in the mechanisms ("adaptations") by which ecologists Physiological include physiolog These mechanisms interact with their environment. frequently organisms and behavior. For a physiological but may also involve anatomy, morphology, ical processes, ecologist,
these
component
processes
achieve
a necessary
integration
at
the whole-organism
traits are employed of "how," the question of "why" specific level. In addition to questions that involves placing adaptive mechanisms is often asked. This is the evolutionary aspect in within more encompassing is providing strategies. ecology Increasingly, physiological
342
at the population (what controls reproductive output?), community sights into phenomena and ecosystem (what traits determine competitive (how do plants respond to her success?), levels. Increasingly, requirements affect feeding strategies?) bivory? How do animal metabolic these other ecological disciplines are providing an added relevance for physiological ecology. 6Ecology and Systematics Cornell University Ithaca, New York 14853
David M. Gates7 the response of organisms to their environments To understand as thoroughly and rigorously as possible all pieces of the problem. known
correctly
(radiation,
temperature,
food,
nutrients,
etc.)
The
one needs to understand The environment must be organism
must
be
known
to radiation, rate, size, absorptance correctly (metabolic rate, respiration rate, photosynthetic on temperature, insulation, etc.), including all the functional relationships (dependencies light, the genotypic and phenotypic variations and carbon dioxide, nitrogen, etc.). Furthermore, of the various properties and functions must be understood. dependencies Clearly this in volves understanding soils, physiology, anatomy, and even physics, meteorology, genetics, The use of such terms is unfortunate, because their use constrains one's think biochemistry. it be physical or is high-quality science irrespective of labels, whether ing. What one desires biological science. but the methodology will use that the goal is ecological, ecology suggests Physiological involves its interactions with information. However, the ecology of an organism physiological the community of organisms inwhich it is immersed and includes competition, succession, and population dynamics. To understand physiology per se is not the goal, but only a means to an end, the end being the ecology of the organism. Environmental has physi physiology information to achieve that goal. The goal is the ology as the goal, but uses environmental factor here. distinguishing Most plant and animal responses to environmental conditions must ultimately be measured in the spond
field, although to a multitude
laboratory of variables,
measurements and
usually
are several
often
necessary are variables
as
well.
varying
Organisms at any moment.
re
must allow for this simultaneity of change. Plants and animals are in transient Measurements relate to transient states states very often. Many challenging physiological ecology questions for of short duration: the effects of sunfleeks on the productivity of understory vegetation, example.
7Biology Station University of Michigan Ann Arbor, Michigan 48109
Bernd Heinrich8 An organism must respond to at least two different components of its environment. One that elicits adaptive response concerns from the physical world. The component challenges that requires response originates from the biosphere. other major challenge Inmy opinion, the aim of physiological is to determine physiological bases or limits ecology to its physical environment. that affect an organism's The behavioral/physiological responses can niche-limits within the environment that the organism capacities ultimately determine of the thermal tolerance and/or thermoregulatory occupy. For example, knowledge capacity of insects of various sizes might allow one to make some predictions of weather conditions or geographically), that exclude certain insects physically but favor (diurnally, seasonally, others. Given a physiological sharpened explanation, by biophysical insights, for observed one can then either examine potential that could act to circumvent responses phenomena, an organism's limits so as to broaden its niche, or the other type of environ physiological mental factors, such as low energy supplies and competitors, it. that might contract concern The data, as such, with which physiological themselves may not be ecologists concerns the interpretation of physiology and homeostatic mecha unique. The uniqueness to the environment, and hence on evolution. The same data on nisms in terms of adaptation in the realm of comparative for example, might also be considered thermor?gulation, physi
343
because
ology,
The
thermy.
file
be used
they could one
uses
to make
to categorize
general
depends
on
statements one's
broader
about frame
body size and endo of
reference.
of Zoology department of Vermont University Burlington, Vermont 05405
B. Huey9
Raymond
is the study of interactions of organisms with each other and with the physical Ecology is the exploration of underlying mechanistic that environment, whereas physiology processes inter how organisms work. Physiological influence ecological determine capacities strongly to elucidate actions of organisms. these influences should Nevertheless, ecologists wishing over many years by not unhesitatingly methods adopt the elegant experimental developed con and physiologists ask complementary but different questions physiologists. Ecologists a study suitable for one field may not be suitable for the Consequently, cerning physiology. other.
Level of Analysis reflects the integration of many component each of processes, performance Organismal to a given environmental which may respond differently variable. Thus organismal perfor mance in nature, the primary focus of ecologists, from studies is more reliably predicted rather than from those directed at isolated tissues or biochemical directed at whole organisms can In contrast, the mechanistic bases of performance, the focus of physiologists, reactions. be determined only from lower level studies. over Behavior
Control
and Morphology
interactions Behavioral and morphological adjustments mediate an animal's physiological in nature can be reliably predicted only from experi and performance. Thus, performance Lower level studies exclude ments permitting animals to use these adjustments. such ad for of but not for prediction of organismal this is mechanisms, analyses justments: appropriate performance.
Acclimation The recent history of an organism influences its capacity and performance. Most terrestrial that can have complex and often unpredictable live in fluctuating environments organisms in nature is more reliably predicted from experi effects on physiology. Thus, performance in which
ments
animals
and especially
anistic, acclimation
have
been
comparative,
exposed
studies
to natural
acclimation
in physiology
regimes.
may
In contrast,
require exposure
mech
to constant
regimes.
of Zoology NJ-15 department University of Washington 98195 Seattle, Washington
Daniel
H.
Janzen10
function with respect to is the study of how physiological processes ecology Physiological or are generated The stress is on 'inter environment, by interactions with the environment. to bogs. If a study in actions' and they may be with anything from subcellular components in kidney blood processing rate) is fo comparative (e.g., interspecific variation physiology the variation that generate cused on the processes (e.g., water and toxin content of the It is a very human trait to concoct animals' foods) it is also a study in physiological ecology. environmental clubs (ecophysiology, ecology, etc.) and design the physiology, physiological into physiological, the subdivision of ecology rules so as to benefit the members; membership a is detrimental etc. is encouraging through (and generally severely straining population, can only have political or eco and certainly further subdivision narrowing of perspective), nomic
344
motives.
in physiological The important kinds of problems ceptual and general framework of understanding, specific
examples,
so
that
we
can
talk
about
both
ecology are those that enlarge our con and those that fill in the interstices with central
tendency
and
variation
in nature's
faced by organisms solutions to the physiological challenges (e.g., what fraction of developing inwhich habitats). Use and appropriateness fruits bear chlorophyllous of method embryos and tools are specific to the question and organism rather than some imagined subdiscipline. It is appropriate to examine that We study how organisms interact with their environments. mor interaction at all levels of organization cellular, physiological, (molecular, biochemical, individual, family, population, habitat, etc.). The 'importance' of physiological phological, is merely that it represents one of these levels. ecology 10Department of Biology University of Pennsylvania Philadelphia, Pennsylvania
James
R.
19104
King11
An essay of 250 words enforces a dogmatic approach, and the following observations about are ex cathedra therefore animal physiological of shorn pronouncements ecology redeeming weasel words. Organismal behavioral, adjustments, broadly speaking, may be morphological, or physiological, re and can involve either genotypic responses (speciation) or phenotypic to proximate environmental factors in present time. Only the latter are in the realm sponses or physiological of environmental Environmental physiology ecology. physiology typically to abiotic factors, most commonly in the laboratory, focuses on physiological responses or the life-styles of free-living organisms. The em without reference to natural environments of response or the limits of physiological phasis is on mechanisms plasticity (e.g., CNS control of thermal panting, renal or sweat-gland to water shortage or dehydration). The adjustments textbooks by Folk or Slonim (editor) entitled "Environmental exemplify this per Physiology" In contrast, physiological spective. ecology focuses not only on physiological adjustments by in which morphological the phenotype, but also on the ways and behavioral adjustments limitations. The investigation of operational ameliorate or substitute for physiological factors in natural microenvironments is an essential of phys component (biotic as well as abiotic) or and other species (through competition iological ecology. To the extent that conspecifics or access to nutrients, for instance, they may indirectly pr?dation) affect energy expenditure necessitate and thus constitute environmental factors within the physiological adjustments, scope of physiological ecology merges with behav ecology. At this interface, physiological ioral ecology. As yet there are no textbooks on physiological ecology. Gates' "Biophysical In short, the key concepts of physiological is the closest approximation. Ecology" ecology that can guide editors who insist on distinguishing environmental physiology or comparative from physiological natural mi responses, physiology ecology are: phenotypic physiological or behavioral croenvironmental substitutes for physiological variables, and morphological even capacities. Finally, readers should notice that I have not used the word "adaptation" once.
of Zoology "Department State University Washington 99164 Pullman, Washington
Polley Ann McClure12 inwhich the questions is a branch of biological science have their ecology Physiological level and their answers at the level of organismal or origins at the evolutionary or ecological in which the focus of This differs from comparative physiology suborganismal physiology. and sub-organismal is a specific organismal process and a variety of organism questions inwhich Italso differs from environmental "tools" are used to study the process. physiology the focus is on a specific (usually stressful) environmental factor such as altitude, cold, heat, and the organism's to that factor. responses physiological The questions and eco important concern basic issues of evolutionary characteristically of the of The differentiation. methods for studies basis range example logical biology, ecotypic to precise biochemical correlation and physical measure from fairly descriptive analyses
345
ments,
sometimes
in the
context
of
designed
experiments,
sometimes
not.
The
methods
are
ecology except that, where possible, they are increasingly usually not unique to physiological The most obvious example here being adapted for use in the animal's natural environment. rate. Most studies employ the procedures is the method of measuring metabolic for measuring in use in physiology and carbon dioxide production laboratories, but oxygen consumption we are having increasing success in measuring rate in the field using doubly la metabolic It is important that physiological belled water. those ques differentiate between ecologists and those that require new methods, tions answerable with standard physiological methods and that they expend the effort to develop appropriate and precise techniques. The relationship of physiological ecology to population and community ecology on the one and biophysics on the other, is that of a bridge between two otherwise hand, and biochemistry can provide the ecological isolated land masses. "so what?" at the ecology Physiological in otherwise esoteric chemical and and community level to studies of variations population It can also provide the predictability at the ecological level that comes physical processes. based on fundamental principles of chemistry and phys foundations from sound mechanistic ics.
12Department of Zoology Indiana University Indiana 47401 Bloomington,
Brian
K. McNab13
taken from natural history, ecol is an intellectual brew of elements Physiological ecology It and tied to the experimental of physiology. and evolution, ogy, operationally discipline but in and environmental not in subjects or techniques, differs from comparative physiology, goals: the former is principally concerned with the integrative view of ecology and evolution, the latter with reductionism. Physiology brings to ecology an analytic approach based in the as to how far mathematics can be used to there is sciences, disagreement although physical of organisms without unduly idealizing the problems. Ultimately, the analyze the responses is the nature of, and the limits to, adap principal concern of most physiological ecologists tation. As these limits are approached, examine the means by which physiological ecologists into a functional basis for the limits such limits are evaded, or how these limits are translated to climatic and geographic distribution. This field also has significance for other disciplines, such as population (in that the reproduction of animals appears to depend on their ecology or community ecology rates of energy expenditure) (where energy distribution and exchange the size of individuals and the in communities vary significantly with the trade-off between is a thorough understanding size of populations). ecology Finally, the bedrock of physiological not does influence such knowledge of the natural history of the organisms studied; only being but it can suggest which species should be studied to the interpretation of our observations, the diversity of life on the planet Earth. determine the rules by which evolution has produced 13Department of Zoology University of Florida Florida 32611 Gainesville,
Phillip C. Miller14-15 attributes ecology should include as its domain of interest the physiological Physiological that allow them to live in and restrict them to their natural habitat or ecosystem. of species or en variable is the organism's The dependent place in nature. In comparative physiology variable or the focus of interest is on the internal and the dependent vironmental physiology, or species to its habitat. While the foci of the of an organism adjustments morphological both may involve evolutionary differ in direction of emphasis, interpretations and disciplines or measurements. Historically, physiological ecology may utilize similar research techniques As these in the United States has emphasized plant water and carbon balance measurements. of better techniques for syn have become better known, and with the development aspects on the and to water balance whole of carbon information processes, plant linkages thesizing These functioning have been developed. plant behavior, population attributes, and ecosystem a means areas are the to the current of active research; develop provide sig they linkages
346
nificance general
of detailed mechanistic
physiological basis
in a fuller ecological
attributes at
for observations
the
and
population
setting,
a
and to develop
community
level.
14Systems Ecology Research Group San Diego State University San Diego, California 92115 15Deceased
Park S. Nobel16 To me there is no sharp distinction among plant physiology, environmental plant physiol and a biophysical ogy, physiological plant physiology), plant ecology (or ecological plant In fact, I have taught courses with titles in all four areas and the material has over ecology. lapped considerably. in plant ecology, such The objective of ecological is to explain processes plant physiology as plant performance, in physiological, survival, and distribution, biochemical, biophysical, and molecular that we cannot only be preoccupied with events at the terms. This means molecular levels, but must also broach broader questions. At one extreme, we find the phys with states and processes within relatively small scales of space and iologist preoccupied time. These concerns of adaptation in terms of the way component lead to understanding are fitted together for optimal performance in a partic of the individual organism processes ular habitat. At the other extreme, we find the ecologist much with preoccupied larger scale inwhich the survival of the individual organism states and processes, is but one component of the performance of the larger system, the ecosystem. These two views lead to a concern with the physiology within the environmental of performance limits to survival on the one hand, and the biology of survival on the other. 16Department of Biology University of California Los Angeles, California
90024
Boyd R. Strain17 inwhich physiological As the term implies, this is a discipline techniques are used to study is the noun and physiology an adjective. Thus, ecology remains problems. Ecology ecological or comparative the primary objective. Environmental physiology, ecophysiology, physiology, on the other hand, imply that physiological are at the center of the scientific curi questions osity.
Physiological ecology of organisms responses biological
interaction.
can be addressed
is generally practiced at the organism allows the analysis of the integrated Supraorganism
by monitoring
taxonomic-,
certain
population-,
physiological
level. Studying physiological effects of environmental and or
ecosystem-level
characteristics
questions
of representative
or
ganisms.
It is true that a physiological ecologist will frequently have to work at the suborganismal level. The stated objective of the experiment and the interpretation of results, however, will be both integrative and extrapolative. The ecologist will not stop at an explanation of the examined but will go on to a discussion mechanism of how that mechanism physiological affects the establishment and survival of the organism or species. Insummary, all ecologists in relation to their environment. A physiological study organisms in that study. Somewhat in jest, I tell my ecologist simply uses physiological techniques drive four-wheelers, wear desert boots, and use Scho students that physiological ecologists lander bombs, while environmental drive sedans, wear dress shoes, and use physiologists are valid, of course. Neither is innately preferable to the Waring Blenders. Both approaches other. In fact, a given investigator may be an ecologist in one study and a physiologist in another.
17Department of Botany Duke University Durham, North Carolina
27706
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