Fundamentals of EcologyFIFTI { EDITION

Eugene P. Odum, Ph.D.Late oJ University oJ Georgla Institute oJ Ecologt

Gary W. Barrett, Ph.D.Odum ProJessor of Ecolog4 University oJ Geor$a Institute of Ecologt

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1

The Scope of Ecology

Ecology: History and Relevance toHumankindLevels-of .Organization HierarchyThe Emergent Property PrincipleTranscending Functions and ControlPro@ssesEcological IntertacingAbout ModelsDisciplinary Reductionism to TransdisciplinaryHolism

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Iable 1-1

1 Ecology: History and Relevance to llumankind

The word ecologi is derived from rhe Greek oihos, meaning "household," and logos,meaning "study." Thus, the study of the environmental house includes all the organ-isms in it and all the functional processes that make the house habitable. Literally,then, ecology is the study o[ "life at home" with emphasis on "the totality or pat-tern of relations between organisms and their environment," to cite a standard dic-tionary definition of the word (Merriam -Webster's Collegiate Dictionory, 1Oth edition,s.v. "ecology").

The word economics is also derived from the Greek root oikos. As nom[s means"management," economics translates as "the management of the household" and, ac-cordingly, ecology and economics should be companion disciplines. Unfortunately,many people view ecologists and economists as advercaries with antithetical visions.Table 1-1 attempts to illustrate perceived differences between economics and ecol-ogy. l-ater, this book will consider the confrontation that resuhs b€cause each disci-pline takes a narrow view of its subject and, more important, the rapid developmentof a new interface discipline, ecoiogical economics, that is begnmng to bridge the gapbetween ecology and economics (Costanza, Cumberland, et al. I997; Barrett and Fa-rina 2000; L. R. Brown 2001).

Ecologlr was of practical interest early in human history. In primitive society, allindividuals needed to know their environment-that is, to understand the forces ofnature and the plants and animals around them-to survive. The beginning of civi-lization, in fact, coincided with the use of fire and other tools to modify the environ-ment. Because o[ technological achievements, humans seem to depend less on thenatural environment for their daily needs; many of us lorget our continuing depen-dence on nature for air, water, and indirectly, food, not to mention waste assimila-tion, rccreation, and many other s€rvices supplied by nature. Also, economic systems,of whatever political ideology, value things made by human beings that primarilybenefit the individual, but they place little monetary value on the goods and servicesof nature that benefit us as a society. Until there is a cdsis, humans tend to uke nat-

A summary of perceived differences between economics and ecology

Atttibute Economics Ecologl

School of thought

Currency

GroMh form

Selection pressure

Technological approach

System services

Resource use

System regulation

Futuristic goal

Cornucopian

Money

J-shaped

r-selected

High technology

Services providedby economic capital

Linear (disposal)

Exponential expansion

Exploration and expansion

Neo-Malthusian

Energy

S-shaped

K-selected

Appropriate technology

Services providedby natural capital

Circular (recycling)

Carrying capacity

Sustainability and stability

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SECTION 1 Ecology: History and Relevance to Humankind 3

Figute 1.1. Earthscape as viewed from Apollo 1 7 travel-ing toward the Moon. Mew of the ecosphere from "outsidethe boxl'

ural goods and services for granted; we assume they are unlimited or somehow re-placeable by technological innovations, even though we know rhar life necessitiessuch as oxygen and water may be recyclable but nor replaceable. As long as the life-support seruices are considered free, they have no value in current market systems(see H. T. Odum and E. P Odum 2000).

Like all phases of learning, the science of ecology has had a gradual if spasmodicdevelopment during recorded history. The writings of Hippocrates, Aristotle, andother philosophers ol ancient Greece clearly contain references to ecological topics.However, the Greeks did not have a word for ecology. The word ecolog,, is o[ recenrorigin, having been frrst proposed by the G€rman biologist Ernst Haeckel in 1869.Haeckel defined ecolosl as "the study of the natural environmem including rhe re-lations of organisms to one another and to their surroundings" (Haeckel 1869). Be-fore this, during a biological renaissance in the eighteenth and nineteenth centuries,many scholars had contributed to the subject, even though the word ecologr was notin use. For example, in the early 1700s, Antoni van Leeuwenhoek, best known as apremier microscopist, also pioneered the study of food chains and population regu-Iation, and the writings of the English botanist Richard Bradley revealed his under-standing of biological productivity. All three of these subjects are important areas ofmodern ecology.

As a recognized, distinct field ofscience, ecology dates from about 1900, but onlyin the past few decades has the word become part of the general vocabulary. At first,the field was rather sharply divided along taxonomic lines (such as plant ecology andanimal ecologl), but the biotic community concept of Frederick E. Clements andVictor E. Shelford, the food chain and material cycling concepts of Ra1'rnond Linde-man and G. Evelyn Hutchinson, and the whole iake studles o[ Edward A. Birge andChauncyJuday, among others, helped establish basic theory for a unified 6eld ofgen-eral ecology. The work of these pioneers will be cited often in subsequent chapters.

What can best be described as a worldwide environmental awareness movementburst upon the scene duing two years, 1968 lo 1970, as astronauts took the firstphotographs of Earth as seen from outer space. For the first time in human history,we were able to see Eanh as a whole and to realize how alone and fragile Earth hov-ers in space (Fig. I-1). Suddenly, during the 1970s, almost everyone became con-

4 CHAPTER 1 The Scope of Ecology

BIOTIC COMPONENTS

plus

ABIOTIC COMPONENTS

equals

BIOSYSTEMS

cemed about pollution, natural areas, population growrh, food and energ/ con-sumption, and biotic diversity, as indicated by the wide coverage of environmentalconcerns in the popular press. The 1970s were frequently referred to as the "decadeof the enyironment," initiated by the first "Earth Day" on 22 April 1970. Then, in the1980s and 1990s, environmental issues were pushed into the political backgroundby concerns for human relations-problems such as crime, the cold war, govern-ment budgets, and welfare. As we enter the early stages of the twenty-first century,environmental concelns are again coming to rhe forefront because human abuse o[Earth continues to escalate. We hope that this time, to use a medical analogy, our em-phasis will be on prev€ntion rather than on treatment, and ecology as outlined in thisbook, can contibute a great deal to prevention technology and ecosystem health(Barrett 2001).

The increase in public attention had a profound effect on academic ecology. Be-fore the 1970s, ecology was viewed largely as a subdiscipline of bioiogy. Ecologisrswere staffed in biology depanmenrc, and ecology courses were generally found onlyin the biological science curricula. Although ecology remains strongly rooted in bi-ology, it has emerged from biologr as an essemially new, inregrarive discipline tharlinks physical and biological processes and forms a bridge berween rhe natural sci-ences and the social sciences (E. P Odum 1977). Most colleges now offer campus-wide courses and have separate majors, departments, schools, centers, or inslitutes ofecology. While the scope of ecology is expanding, the study of how individual or-ganisms and species interface and use resources intensifies. The multilevel approach,as outlined in the next section, brings together "evolutionary" and "systems" think-ing, two approaches that have tended to divide the field in recent years.

2 levels-of-0rganizationHierarchy

Perhaps the best way to delimit modern ecology is to consider the concept o[ levelsof organization, visualized as an ecological spectrum (Fig. 1-2) and as an extendedecological hierarchy (Fig. 1-3). Hierarchy means "an arrangement into a gradedsetes" (Merriam-Webster's Collegiete Dicfionary, 10th edition, s.v. "hierarchy"). Inter-action with the physical environment (energy and matter) at each level producescharacteristic functional systems. A system, according to a standard defrmuon, con-sists of "regularly interacting and interdependent components forming a unified

Genes Cells Organs Organisms Populations Communitiest{ ++ t+ t+ t+ r{

Matter Energy

[ | |Genetic Cell Organ Organismic Population Ecosystemssystems syslems systems systems systems

Figure 1-2. Ecological levels-ot-organization spectrum emphasizing the interaction of living(biotic) and nonliving (abiotic) components.

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Figure 1-3. Ecological levels-of-organization hierarchy; seventranscending processes or lunc-tions are depicted as verticalcomponents of eleven integra-tive levels of organization (afierBarrett et al. 1997).

EnergeticsEvolution

DevelopmentRegulation

BehaviorDiversityIntegration

whole" (Meriam-Webster's Collegiate Dictiondry, l0th edirion, s.v .system"). Systemscontaining living Giotic) and nonliving (abioric) components constirure biosrstems,ranging from genetic systems to ecological sysrems (Fig. I-2). This specrmm maybe conceived of or srudied at any level, as illusrrated in Figure 1-2, oi at any inter_mediate position convenient or practical for analysis. For example, host-parasire sys_tems or a two-species system of mutually linked organisms (such as the fungi_algaepartnership that constitutes the lichen) are intermediate levels between oooulationand community.

Ecology is largely, bur not entirely, concerned with the system levels beyond thatof the organism (Figs. 1-3 and 1-4). ln ecology, rhe rerm population, originallycoined to denote a group of people, is broadened ro include groups ofindividuals ofany one kind o[ organism. Likewise, cornmunity, in rhe ecological sense (sometimesdeslgnated as "biotic community"), includes all the populations occupying a givenarea. The community and the nonliving environment function together as an eco_logical system or ecosyst€m. Biocoenosis andbiogeocoenosis (lireralt, ..lfe and Earth

6 C HAPTE R 1 The Scope of Ecology

Figure 1.4. Compared with the strong set-point controlsat the organism level and below, organization and lunction atthe population level and above are much less tightly regu-lated, with more pulsing and chaotic behavio( but they arecontrolled nevertheless by allernating positive and negativefeedback-in other words, they exhibit homeorhesrs as op-posed to homeostasls. Failure to recognize this difference incybernetics has resulted in much confusion about the bal-ance of nature.

Ecosphere

1Biomes

ILanoscapes

tEcosystems

tCommunities

tPopulations

t

No sefpoint controlsfeedback (+ and -)

maantaanjngpulsing stateswithin l imits

HOMEORHESIS

OFGANISM

IOrgan systems

II

Tissues

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IMolecules

IAtoms

Sel-point controlsfeedback (+ and -)

maintainingsteady stateswithin l imits

HOMEOSTASIS

functioning together"), terms frequently used in European and Russian lirerarure, areroughly equivalent to community and ecosystem, respectively. Refe[ing again toFigure 1-3, the next level in the ecological hierarchy is the landscape, a term origi-nally referring to a painting and defined as "an expanse of scenery seen by the eye asone view" (M€rridm -Webster's Colleglo.te Dictionary, lOth edition, s.v. "landscape"). lnecology, landscape is defrned as a "heterogenous area composed o[ a cluster of in-teracting ecosystems that are repeated in a similar manner throughout" (Forman andGodron 1986). A wctershed is a convenient landscapeJevel unit for large-scale studyand management because it usually has identifiable natural boundaries . Biome is aterm in wide use for a large regional or subcontinental system characterized by a ma-jor vegetation t)?e or other identifying landscape aspect, as, for example, the Tem-perate Deciduous Forest biome or the Continental Shelf Ocean biome. A reglon is alarge geological or political area that may contain more than one biome-for ex-ample, the regions of the Midwest, the Appalachian Mountains, or the Pacific Coast.The largest and most nearly self-sufficient biological sysrem is ofren designated as rheecosphere, which includes all the living organisms of Earth interacting with thephysical environment as a whole to maintain a self-adjusting, loosely controlled puls-ing state (more about the concept of "pulsing state" Iater in this chapter).

Hierarchical theory provides a convenient framework for subdividing and exam-ining complex situations or extensive gradients, but it is more thanjust a useful rank-order classification. lt is a holistic approach to understanding and dealing with com-

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piex siruations, and is an alternative to the reductionist approach of seekrng answersby reducing problems ro lower-level analysis (Ahl and Allen 1996).

More than 50 years ago, Novikoff (1945) poirued out that rhere is both continu-ity and discontinuity in the evolurion of the universe. Development may be viewedas continuous because it involves never-ending change, but it is also drsconLtnuousbecause it passes rhrough a series of different levels of orqanizarion. As we shall dis_cuss in Chapter 3, the organized state o[ Ii[e is mainraineJ by a conrinuous but srep-wise flow ofenergy. Thus, dividing a graded series, or hierarchy, into components isin many cases arbitrary, but sometimes subdivisions can be based on natural discon_tinuities. Because each level in the levels-of-organization spectrum is ,.integrated" orinterdependent with other levels, there can be no sharp lines or breaks in a functionalsense, nor even between organism and population. The individual organism, for ex_ample,

-cannot survive for long without its population, any more than the organwould be able [o survive for long as a self-perpetuaring unit without its organlsm.Similarly, the community cannot exist wirhour rhe cyclinq of materials and the flowof energy in rhe ecosysrem. This argumenr is applicable t"o rhe previously discussedmistaken notion that human civilization can exist separately from the natural world.

It is very rmporrant to emphasize thar hierarchies in nature are nested-Lhar ts,each level is made up of groups of lower-level unirs (populations are composed ofgroups of organisms, for example). ln sharp contrast, human-organized hierarchiesrn Sovernments, cooperations, univercities, or the military are nonnested (sergeantsare not composed ofgroups ofprivates, for example). Accordingly, human-organizedhierarchies tend ro be more rigid and more sharply separated ii compared ro natu_ral levels o[ organization. For more on hierarchrcal theory, see T. F. H. Allen and Starr(1982), O'Neil l et al. (1986), and Ahl and Allen (1996).

3 The Emergent Propefi Principte

Al important consequence of hierarchical organization is that as componems, orsubsets, are combined to produce larger functional wholes, new propenies emergethat were not preseni at the level below Accordingly, an emergent property of inecological level or unit cannot be predicted from the study of the components of thatlevel or unit. Another way to express rhe same concept rs nonreducibie propeny-that is, a property ofthe whole not reducible to the sum ofrhe propenies of the parts.Though findings at any one level aid in the study of the next level, they never com_pletely explain the phenomena occurring ar the nexr level, which musr itselfbe stud-ied to complete rhe picrure.

Two examples, one from the physical realm and one from rhe ecological realm,will suffice to illusrrate emergent properries. When hydrogen and oxygen are com-bined in a certain molecular configuration, water is formed-a liquid wirh proper-ties utterly different from those of its gaseous components. When certain algae andcoelenterate animals evolve together to produce a coral, an efficient nutrientiyclingmechanism is created that enables the comblned system to maintain a high rate ofproductivity in waterc with a very low nutrient content. Thus, the fabulous produc-

8 CHAPTER 1 The Scope of Ecology

tivity and diversity of coral reefs are emergent propenies only at the level of the reefcommunity.

Salt (1979) suggested that a distinction be made between emergem propeties, asdefined previously, and collective properties, which are summations of the behav-ior of components. Both are properties of the whole, but the collective properties donot lnvolve new or unique characteristics resuking from the functioning of the wholelniL Birth rate is an example of a population level collective property, as it is merelya sum of the individual births in a designaied time period, expressed as a lraction orpercent of the total number of individuals in the population. New properties emergebecause the components interact, not because the basic nature of the components ischanged. Parts are not "melted down," as it were, but integrated to produce uniquenew properties. lt can be demonstrated mathematically that integrative hierarchiesevolve more rapidly from their constituents than nonhierarchical systems with thesame number of elements; they are also more resilient in response to disturbance.Theoretically, when hierarchies are decomposed to theirvarious levels oIsubsysrems,the latter can still interac[ and reorganize to achieve a higher level of complexity.

Some attributes, obviously, become more complex and variable as one proceedsto higher levels of organization, but often other attributes become less complex andless variable as one goes from the smaller to the larger unit. Because feedback mech-anisms (checks and balances, forces and counterforces) operate throughout, the am-plitude ol oscillations tends to be reduced as smaller units function within largerunits. Statistically, the va ance of the whole system level property is less than thesum of the variance of the parts. For example, the rate of photosynthesis of a foresrcommunity is less variable than that of individual leaves or trees within the commu-nity, because when one component siows down, another component may speed upto compensate. When one considers both the emergent propenies and the increasinghomeostasis that develop at each level, not all component parts must be known be-fore the whole can be understood. This is an important point, because some contendthat it is useless to try to work on complex populations and communities when thesmaller units are not yet fully understood. Quite the contrary, one may begin studyat any point in the spectrum, provided that adjacent levels, as well as the level inquestion, are considered, because, as already noted, some attributes are predictablefrom parts (collective properties), but others are no[ (emergent properties). ldeally, asystem-level studyis itselfa threefold hierarchy: system, subsystem (next levelbelow),and suprasystem (next level above). Formore on emergenl properties, see f. F. H. AIIenand Starr (1982), T. F. H. Allen and Hoekstra (1992), and Ahl and Allen (1996).

Each biosystem level has emergent properties and reduced variance as well as asummation of attributes of its subsystem components. The folk wisdom about theforest being more than just a collection of trees is, indeed, a first working principleof ecology. Although the philosophy of science has always been holistic in seeking tounderstand phenomena as a whole, in recent years the practice of science has becomeincreasingly reductionist in seeking to understand phenomena by detailed study ofsmaller and smaller componenls. LaszLo and Margenau (1972) described within thehistory o[ science an alternation of reductionist and hoiistic thinking (redi{ctiorxism

constructionism and atomism-holism are other pairs of words used to contrast thesephilosophical approaches). The law of diminishing retums may very well be involvedhere, as excessive ellort in any one direction eventually necessitates taking the other(or another) direction.

The reductionist approach that has dominated science and technology since lsaac

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SECTION 4 Transcending Functions and Control Processes 9

Newton has made major contdbutions. For example, research at the cellular and mo-lecular levels has established a firm basis for the future cure and prevention of can-cers at the level of the organism. However, celllevel science wiil contribute very littleto the well-being or survival of human civilization if we understand the higher levelsof organization so inadequately that we can hnd no solutions to population over-growth, pollution, and other forms ofsocietal and environmental disorders. Both ho-lism and reductionism must be accorded equal value-and simultaneously, not al-tematively (E. P Odum 1977; Barrett 1994). Ecology seek slnthesis, not separation.The revival of the holistic disciplines may be due at least partly to citizen dissatisfac-tion with the specialized scientist who cannot respond to the large-scale problemsthat need urgent attention. (Histodan L),nn White's 1980 essay "The Ecology of OurScience" is recommended readlng on this viewpoint.) Accordingly, we shall discussecological principles at the ecosystem level, with appropiate attention to organism,population, and community subsets and to landscape, biome, and ecosphere supra-sets. This is the philosophical basis for the organization o[ the chapters in this book.

Fortunately, in the past I0 years, technological advances have allowed humans todeal quantitatively with large, complex systems such as ecosystems and landscapes.Tracer methodology, mass chemistry (spectrometry, colorimetry, chromatography),remote sensing, automadc monitoring, mathematic modeling, geographical informa-tion systems (GlS), and computer technology are providing the tools. Technology is,of course, a double-edged sword: it can be the means of underctanding the whole-ness of humans and nature or of destroying it.

4 Transcending Functions and Contrul Proeesses

Whereas each level in the ecological hierarchy can be expected to have unique emer-gent and collective prope ies, there arc basic functions that operate at a]l levels. Ex-amples of such transcending functions are behavior, development, diversity, ener-getics, evolution, integration, and regulation (see Fig. l-3 for details). Some o[these(energetics, for example) operate the same throughout the hierarchy, but others dif-fer in modus operandi at different levels. Natural selection evolulion, for example, in-volves mutations and other direct genetic interactions at the organism level but indl-rect coevolutionary and group selection processes at higher levels.

It is especially impoftant to emphasize that although positive and negative feed-back controls are universal, from the organism dom, control is sel ?oirlf, in that it in-volves very exacting genetic, hormonal, and neural controls on growth and develop-ment, Ieading to what is often called homeostasis. As noted on the right-hand sideof Figure 1-4, there are no set-point controls above the organism level (no chemostatsor thermostats in nature). Accordingly, feedback control is much looser, resulting inpulsing rather than sieady states. The term homeorhesis, from the Greek meaning"maintaining the floq" has been suggested for this pulsing control. ln other words,there are no equilibriums at the ecosystem and ecosphere levels, but there are pulsingbclances, such as between production and respiration or between oxygen and carbondioxide in the atmosphere. Failure to recognize this difference in cybernetics (the sci-ence dealing with mechanisms of control or regulation) has resulted in much confu-sion about the realities of the so-called "balance of nature."

10 CHAPTER 1 The Scope ot Ecology

5 Ecologicallnterfacing

Because ecology is a broad, muLtilevel discipline, it inrerfaces well with lraditionaldisciplines that tend to have more narrow focus. During the past decade, there hasbeen a rapid rise of interface fields of study accompanied by new societies, journals,

symposium volumes, books-and new careers. Ecological economics, one of themost important, was mentioned in the frrst section in this chapter. Others that are re-ceiving a great deal oI attention, especially in resource management, are agroecology,biodiversity, conservation ecology, ecologlcal engineering, ecosystem health, ecotox-icology, environmental erhics, and restoration ecology.

In the beginning, an interface effort enriches the disciplines being interfaced.Lines of communication are established, and the experlise o[ narrowly trained "ex-

perts" in each field is expanded. However, for an interface field ro become a new dis-cipline, something new has to emerge, such as a new concept or technology. The con-cept oInonmarket goods and services, for example, was a new concept that emergedin ecological economics, but that inidally neither rraditional ecologists nor econo-mists would put in their textbook (Daily 1997; Mooney and Ehrlich 1997).

Throughout lhis book, we will reler to natural capital and economic capital. Nat-ural capital is defined as the benefits and services supplied to human societies bynatural ecosystems, or provided "free of cosf'by unmanaged natural systems. Thesebenehts and services include purificadon oI water and air by natural processes, de-composition of wastes, maintenance of biodiversity, control of insect pests, pollina-tion o[ crops, mitigation of floods, and provision o[ natural beauty and recreation,among others (Daily 1997).

Economic capital is defined as the goods and services provided by humankind,or the human workforce, tlpically expressed as the gross national product (GNP).

Gross national product is the total monetary value o[ all goods and serl,rces pro-vided in a country during one year. Natural capital is typically quantifred and ex-pressed in units of energy, whereas economic capital is expressed in monetary units(Table 1-1). Only in recent years has there been an attempt to value the world'secosystem services and natural capital in moneury terms. Costanza, d'Arge, et al.(1997) estimated this value to be in the range of 16 to 54 trillion U.S. dollars per yearfor rhe enrire biosphere, with an average of 33 triliion U.S. dollars per year. Thus it iswise to protect natural ecosystems, both ecologically and economically, because ofthe benehts and services they provide to human societies, as will be illustrated in the

chanters that follow.

6 About Models

Ifecology is to be discussed at the ecosystem level, for reasons already indicated, how

can this complex and formidable system level be dealt with? We begn by describingsimplifred versions that encompass only the most important, or basic, properties and

functions. Because, in science, simplified versions of the real world are called models,

it is appropriate now to introduce this concept.A model (by definition) is a formulation that mimics a real-world phenomenon

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SECTION 6 About Mode ls 11

and by which predictions can be made. ln their simplest lorm, models may be verbalor graphic (infotmal). Ultimately, however, models musr be sraristical and mathe-matical Uormdl) i[ their quantitative predictions are ro be reasonably good. For ex-ample, a mathematical formulation that mimics numerical changes in a populationof insects and that predicts the numben in the population at some time would b€considered a biologically useful model. lf the insect population in question is a pestspecies, the model could have an economically important application.

Computer-simulated models permit one to predict probable outcomes as param-eters in the model are changed, as new parameters are added, or as old on€s are re-moved. Thus, a mathematical formulation can often be "tuned" or refined by com-puter operations to improve the "nC'to the real-world phenomenon. Above all,models summarize what is understood about the situation modeled and thereby de-limit aspects needing new or better data, or new principles. When a model does notwork-when it poorly mimics the real world-computer operadons can often pro-vide clues to the refinemenm or changes needed. Once a model proves to be a usefulmimic, opponunities for experimentation are unlimited, because one can introducenew factors or perturbations and see how they would affect the system. Even when amodel inadequately mimics the real world, which is often the case in its early stagesof development, it remains an exceedingly useful teaching and research tool if it re-veals key components and interactions that merit special attention.

Contrary to the feeling of many who are skeptical about modeling the complex-ity of nature, information about only a relatively small number ofvariables is ofren asufficient basis for effectlve models because key factors, or emergent and orher ime-grative properties, as discussed in Sections 2 and 3, often dominate or control a largepercentage ofthe action. Watt (1963), for example, stated, "We do not need a rremen-dous amount o[ information about a great many variables to build revealing mathematical models." Though the mathematical aspects of modeling are a subject for ad-vanced texts, we should review the first steps in model building.

Modeling usually begins with the construction of a diagram, or "graphic model,"which is often a box or companmenL diagram, as illustrated in Figure 1-5. Shown aretwo properties, P1 and P2, that interact, I, to produce or alfect a third prope y, P],when the system is driven by an energy source, E. Five flow pathways, F, are shown,with F1 representing the input and F6 the output for the system as a whole. Thus, ata minimum, there are five ingredients or components for a working model of an eco-logrcal situation, namely, (l) an energ) source or other outside forcing function, E;(2) properties called state variables, P1, Pr, . . . P"; (3) flow pathways, Fr, F2, . . . Fi,showing where energy flows or material transfers connect properties with each otherand with forces; (4) interaction functions, I, where forces and properties interact tomodify, amplify, or control llows or create new "emergenC' properties; and (5) feed-back loops, L.

Figure 1-5 could serve as a model for the production of photochemical smog inthe air over Los Angeles. ln this case, P1 could represent hydrocarbons and P2 nitro-gen oxides, two products of automobile exhaust emission. Under the driving force ofsunlight energy, E, rhese interact to produce photochemical smog, P1. In this case,the interaction function, l, is a slrrergistic or augmentative one, in that P3 is a moreserious pollutant for humans than is P1 or P2 acting alone.

Alternatively, Figure 1-5 could depict a grassland ecosystem in which P1 repre-sents the green planE that convet the energy of the Sun, E, to food. P2 might repre-sent a herbivorous animal that eats plants, and P:l an omnivorous animal that can eat

1 2 C H A P T E R ] The Scope of Ecology

Figure 1-5. Compartment diagram showing the fjve basjc components of primary Interest rnmodeling ecological systems. E : energy source (forcing function); pj, p2, p3 = state variables;F1-F6 = flow pathways; | : interaction function; L = feedback looo.

either the herbivores or rhe plants. ln rhis case, the interaction function, I, could rep-resent several possibil i t ies. Ir could be a no_preference swirch i[ observntron in thereal wotld showecL that the omnivore p, eats either pr or pr, according to availabil ity.Or I could be specified to be a constant percentage value i[ i t was found that rhe diero[ P, rvas composecl of, say, 80 percent plant and 20 percent animal narrer, rrre_specrivc o[ the srate o[ p, or pr. Or I cou]d be a seasonai switch i[ pr feeds on plantsduring one part of the year ancL on animals during anorher season. Or I could be athreshold switch i l P, greatly prelcrs animal food and switches to plants only whenP, is rcduced to a low level.

Fccclbcrch loops are imporLant learures oI ecological models because they repre_sent control mechanisms. Figure l-6 is a simpli l ied diagram oIa system th fearuresa feedback loop in which "downstream,, ourput, or so;e part o[ i i . is fed back or .ecycleci ro affect or perhaps conrrol "upstream., .o.pon.nrs. For exrmple, the feed_back loop could represent predalion by 'downsrream',

organisms, C, that reduce andthereby rend to control the grouth o[,,upstream,' herbivores or plants B and A in thefoocl chain. Often. such a feedback acrually promotes the growth or survival of adownstrcam col]tponent, such as a grazer enhancing fhe growth of plants (a .,rewardfeedback." as it rvere).

Figure 1-6. Compartment model with afeedbackorcon-trol loop that transforms a linear system into a partially cycli-cal one.

Feedback loop

-

t r n

:p-het \ ' '

le t

re-'lt5

l a

c'n

Figute 1.7. Interaction of positiveand negative feedbacks in the relation-ships of atmospheric COr, climatewarming, soil respiration, and carbon se'questration (modified after Luo et al.2001) .

SECTI0 N 6 About Models 13

Figure 1-6 could also represent a desirable economic system in which resources,

A, are converted into useful goods and services, B, with the production ofwastes, C,that are recycled and used again in the conversion process (A --+ B), thus reducing

the waste output of the system. By and large, natural ecosystems have a circular orloop design mther than a linear structure. Feedback and cybernetics, the science of

controls, are discussed in detail in Chapter 2.Figure 1-7 illustrates how positive and negative feedback can interact in the rela-

tionship between atmospheric CO2 concentration and climatic warminS. An increase

in CO2 has a positive greenhouse effect on global warming and on plant growth.

However, the soil system acclimates to the warming, so soil resPiration does not con-

tinue to increase with warming. This acclimation results in a negative feedback on

carbon sequestration in the soil, thus reducing emission of CO2 to the atmosphere,according to a study by Luo et al. (2001).

Compartment models are greatly enhanced by making the shape of the "boxes"

indicate th€ general function of the unit. tn Figure 1-8, some of the symbols from

the H. T. Odum energy language (H. T. Odum and E. P Odum 1982; H. T. Odum

1996) are depicted as used in this book. ln Figure l-9, these s).tnbols are used in a

model of a pine lorest located in Florida. Also, in this diagram estimates of the

amount of energ'y flow through the units are shown as indicators of the relative im-

portance of unit functions.ln summary, good model definition should include three dimensions: (I) the

space to be considered (how the system is bounded); (2) the subsystems (compo-

nents)judged to be important in overall function; and (3) the lime interval to be con-

sidered. Once an ecosystem, ecological situation, or problem has been properly

dehned and bounded, a testable hlpothesis or series o[ hlpotheses is developed that

can be rejected or accepted, at least tentatively, pending further expedmenLation or

analysis. For more on ecological modeling, see Patten and Jorgensen (1995), H. T.

Odum and E. C. Odum (2000), and Gunderson and Holling (2002).

ln the following chapten, the paragraphs headed by the word statement are, in

effect, "word" models of the ecological principle in question. ln many cases, graphic

models are also presented, and in some cases, simplified mathematical formula-

tions are included. Most ofall, this book attempts to provide the principles, concepts,

--> Negative

1 4 C H A P T E R 1 The Scope of Ecology

Energy circuit(A pathway orflow of energy)

Energy source(Source ol energy from

outside the system)

Heat sink(Degraded energyafter use in work)

Producer(Converts and concentrates

sorar ener9yl

Consumer(Uses producer energyfor self-maintenance)

Slorage{A compartment oJ

energy storage)

lnteraclron(Two or more flows

of energy to produce ahigh-quality energy)

Capital transaction(F ow of money to

pay for flow of energy)

-.L--:

-\ t-Y----\. =

t--_r-Y$.-.,.4\---v-*

Figule 1-8, The H. T. Odum energy language symbols used in model diagrams in this book.

Figure 1-9. Ecosystem model usingenergy language symbols and includingestimated rates of energy flow for a Flor-ida pine forest (courtesy of H. T. Odum).

Heat sink (used energy)

-

)k.

SECIION 7 Disciplinary Reductionism to Transdisciptinary Hotism 1O

simplifications, and absrractions that one must deduce from the real world before onecan understand and deal with situations and problems or construct marhematicalmodels of rhem.

7 llisciplinary lieductionism to Tlansdisciptinary Holism

ln a gaper entltled "The Emergence of Ecologr as a New lmegrarive Discipline,,,

E. P Odum (1977) noted that ecology had become a new holistii discipline, havingroots in the biologicai, physical, and social sciences, rather than jusr a iubdisciplineofbiology. Thus, a goal of ecoiogy is to link the natural and sociaisciences. It shouldbe noted that most disciplines and disciplinary approaches are based on increasedspecialization in isolation (Fig. l-10). The early evoiution and development ofecol_

Figure 1.10. Progressionol relations among disciplinesfrom discjplinary reductionismto transdisciplinary holism (af-ter Jantsch 1972).

E

tI

DISCIPLINARYspecialzing in isolat ion

MULTIDISCIPLINARYno cooperation

CROSSDISCIPLINARYrigid polarization towardspecif ic monodiscipl inaryconcepl

INTERDISCIPLINARYcoordination by higherlevelconcept

TRANSDISCIPLINARYmulti-level coordination ofentire education / innovationsystern

16 CHAPTER 1 The Scope of Ecology

ogli was frcquently based on multidisciplinary approaches (multi : "many"), espe-

cially during the 1960s and 1970s. Unfonunately, the multidisciplinary approaches

lacked cooperation or focus. To achieve cooperation and define goals, insliutes or

centers were established on campuses throughout the world' such as the lnstilute of

Ecology located on the campus of lhe University ofGeorgla These crossdisciplinary

uppro".h", (ctott = "traverse": Fig. 1-10) frequently resulted in polarization toward

a specific monodisciplinary concept, a poorly funded administrative unit, or a nar-

row mission. A crossdisciplinary approach also frequently resulted in polarized fac-

uhy reward systems. Institutions of higher leaming, traditiona\ built on disciplinary

structures, have diffrculties in administering programs and addressi.ng environmen-

tal problems as well as taking advantage ofopponunities at greater temporal and spa-

tial scales.To address the dilemma, interdisciPlinary approaches (inter = "among') were

employed, resulting in cooperation on a higher-level concept, problem, or question'

t'oi example, the process and study of natural ecological succession provided a

higher-level concept resulting in the success of the Savannah River Ecological Labo-

ratory (SREL) during its conception. Researchers theorized that new system Proper-ties emerge during the course of ecosystem development and that it is these proper-

ties that largely account for species and growth form changes that occur (E P Odum

1969,1977 , see Chapter 8 for details). Today, interdisciplinary approaches are com-

mon when addressing problems at ecosystem, landscape, and global levels'

Much remains to be done, however. There is an increased need to solve problems,

promote environmental literacy, and manage resources in a transdisciplinary man-

ner. This multilevel, large-scale approach involves entire educalion and innovation

systems (Fig. I-10). Thil integrative approach to the need for unlocking cause-and-

#ect explanations across and among disciplines (achieving a transdisciplinary un-

derstanding) has been termed consilience (E. O Wilson 1998), sustainability scien'e

(Kates et al. 2O0l), and integrative scietLce (Barrett 2001) Actually, the continued de-

velopment ofthe science ofecology (the "study of the household" or''place where we

live';) will likely evolve into that much-needed integrative science of the future This

book attempts to provide the knowledge' concepts, principles, and approaches to

underpin this educational need and learning process