Odum Fundamentals of Ecology

Fundamentals of Ecology FIFTI{ EDITION

EugeneP.Odum,Ph.D. oJEcologt LateoJUniversity oJGeorglaInstitute

GaryW.Barrett,Ph.D. of Ecolog4UniversityoJGeor$aInstituteof Ecologt OdumProJessor

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TheScopeof Ecology Ecology:Historyand Relevanceto Humankind Levels-of.OrganizationHierarchy The EmergentPropertyPrinciple TranscendingFunctionsand Control Pro@sses EcologicalIntertacing About Models DisciplinaryReductionismto Transdisciplinary Holism

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1 Ecology: HistoryandRelevance to llumankind The word ecologiis derived from rhe Greek oihos,meaning "household,"and logos, meaning "study."Thus, the study of the environmentalhouseincludes all the organisms in it and all the functional processesthat make the house habitable. Literally, then, ecology is the study o[ "life at home" with emphasison "the totality or pattern of relationsbetween organismsand their environment," to cite a standarddictionary definition of the word (Merriam-Webster's CollegiateDictionory,1Othedition, s.v. "ecology"). The word economics is also derived from the Greek root oikos.As nom[s means "management,"economicstranslatesas "the managementof the household" and, accordingly, ecology and economicsshould be companion disciplines.Unfortunately, many people view ecologistsand economistsas advercarieswith antitheticalvisions. Table 1-1 attempts to illustrate perceiveddifferencesbetween economicsand ecology. l-ater, this book will considerthe confrontation that resuhsb€causeeach discipline takesa narrow view of its subjectand, more important, the rapid development of a new interfacediscipline, ecoiogical economics, that is begnmng to bridge the gap betweenecologyand economics(Costanza,Cumberland,et al. I997; Barrettand Farina 2000;L. R. Brown 2001). Ecologlrwas of practical interestearly in human history. In primitive society,all individuals neededto know their environment-that is, to understandthe forcesof nature and the plants and animals around them-to survive. The beginning of civilization, in fact, coincided with the use of fire and other tools to modify the environment. Becauseo[ technologicalachievements,humans seem to depend less on the natural environment for their daily needs;many of us lorget our continuing dependence on nature for air, water, and indirectly, food, not to mention wasteassimilation, rccreation,and many other s€rvicessupplied by nature.Also, economicsystems, of whatever political ideology, value things made by human beings that primarily benefit the individual, but they placelittle monetary value on the goodsand services of nature that benefit us as a society.Until there is a cdsis, humans tend to uke nat-

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A summaryof perceiveddifferencesbetweeneconomicsand ecology Atttibute

Economics

Ecologl

Schoolof thought

Cornucopian

Neo-Malthusian

Currency

Money

Energy

GroMh form

J-shaped

S-shaped

Selectionpressure

r-selected

K-selected

Technological approach

Hightechnology

Appropriatetechnology

Systemservices Resourceuse

Servicesprovided by economiccapital Linear(disposal)

Servicesprovided by naturalcapital Circular(recycling)

Systemregulation

Exponential expansion

Carryingcapacity

Futuristicgoal

Exploration and expansion

Sustainability and stability

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SECTION1

Ecology:Historyand Relevance to Humankind 3

Figute 1.1. Earthscape as viewedfromApollo17 traveling towardthe Moon.Mew of the ecospherefrom "outside the boxl'

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ural goods and servicesfor granted; we assumethey are unlimited or somehow replaceableby technologicalinnovations, even though we know rhar life necessities such as oxygen and water may be recyclablebut nor replaceable.As long as the lifesupport seruicesare consideredfree, they have no value in current market systems (seeH. T. Odum and E. P Odum 2000). Like all phasesof learning, the scienceof ecologyhas had a gradual if spasmodic development during recorded history. The writings of Hippocrates,Aristotle, and other philosophersol ancient Greececlearly contain referencesto ecologicaltopics. However, the Greeksdid not have a word for ecology.The word ecolog,,is o[ recenr origin, 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 relations of organismsto one another and to their surroundings" (Haeckel 1869). Before this, during a biological renaissancein the eighteenthand nineteenthcenturies, many scholarshad contributed to the subject,even though the word ecologrwas not in use. For example,in the early 1700s,Antoni van Leeuwenhoek,best known as a premier microscopist,also pioneeredthe study of food chains and population reguIation, and the writings of the English botanist Richard Bradley revealedhis understanding of biological productivity. All three of thesesubjectsare important areasof modern ecology. As a recognized,distinct field ofscience,ecologydatesfrom about 1900, but only in the past few decadeshas the word becomepart of the generalvocabulary.At first, the field was rather sharply divided along taxonomic lines (such asplant ecologyand animal ecologl), but the biotic community concept of Frederick E. Clementsand Victor E. Shelford,the food chain and material cycling conceptsof Ra1'rnondLindeman and G. Evelyn Hutchinson, and the whole iake studles o[ Edward A. Birge and ChauncyJuday,amongothers,helped establishbasictheory for a unified 6eld ofgeneral ecology.The work of thesepioneerswill be cited often in subsequentchapters. What can best be describedas a worldwide environmentalawarenessmovement burst upon the sceneduing two years, 1968 lo 1970, as astronautstook the first photographsof Earth as seen from outer space.For the first time in human history, we were able to seeEanh as a whole and to realizehow alone and fragile Earth hovers in space(Fig. I-1). Suddenly,during the 1970s,almosteveryonebecamecon-

4

C H A P T E R1

The Scope of Ecology

cemed about pollution, natural areas,population growrh, food and energ/ consumption, and biotic diversity, as indicated by the wide coverageof environmental concernsin the popular press.The 1970swere frequently referred to as the "decade of the enyironment,"initiated by the first "Earth Day" on 22 April 1970. Then, in the 1980s and 1990s, environmental issueswere pushed into the political background by concerns for human relations-problems such as crime, the cold war, government budgets,and welfare.As we enter the early stagesof the twenty-first century, environmental concelns are again coming to rhe forefront becausehuman abuseo[ Earth continuesto escalate.We hope that this time, to usea medical analogy,our emphasiswill be on prev€ntionrather than on treatment,and ecologyas outlined in this book, can contibute a great deal to prevention technology and ecosystemhealth (Barrett2001). The increasein public attention had a profound effecton academicecology.Before the 1970s, ecologywas viewed largely as a subdiscipline of bioiogy. Ecologisrs were staffedin biology depanmenrc,and ecologycourseswere generallyfound only in the biological sciencecurricula. Although ecology remains strongly rooted in biology, it has emergedfrom biologr as an essemiallynew, inregrarivediscipline thar links physical and biological processesand forms a bridge berweenrhe natural sciencesand the social sciences(E. P Odum 1977). Most collegesnow offer campuswide coursesand haveseparatemajors,departments,schools,centers,or inslitutes of ecology.While the scope of ecology is expanding, the study of how individual organismsand speciesinterfaceand useresourcesintensifies.The multilevel approach, as outlined in the next section,brings together "evolutionary" and "systems"thinking, two approachesthat have tended to divide the field in recentyears.

2 levels-of-0rganizationHierarchy Perhapsthe best way to delimit modern ecologyis to consider the concept o[ levels of organization, visualizedas an ecologicalspectrum (Fig. 1-2) and as an extended ecologicalhierarchy (Fig. 1-3). Hierarchy means "an arrangementinto a graded setes" (Merriam-Webster's CollegieteDicfionary,10th edition, s.v. "hierarchy"). Interaction with the physical environment (energy and matter) at each level produces characteristicfunctional systems.A system, accordingto a standarddefrmuon, consists of "regularly interacting and interdependent components forming a unified

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

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Figure 1-3. Ecologicallevelsof-organization hierarchy;seven transcending processesor lunctions are depicted as vertical componentsof elevenintegrative levelsof organization (afier Barrettet al. 1997).

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whole" (Meriam-Webster'sCollegiateDictiondry,l0th edirion, s.v .system").Systems containing living Giotic) and nonliving (abioric) componentsconstirure biosrstems, ranging from genetic systemsto ecologicalsysrems(Fig. I-2). This specrmm may be conceivedof or srudied at any level, as illusrrated in Figure 1-2, oi at any inter_ mediateposition convenientor practical for analysis.For example,host-parasiresys_ tems or a two-speciessystemof mutually linked organisms(such as the fungi_algae partnership that constitutesthe lichen) are intermediatelevels between oooulation and community. Ecologyis largely,bur not entirely,concernedwith the systemlevelsbeyond that of the organism (Figs. 1-3 and 1-4). ln ecology, rhe rerm population, originally coined to denotea group of people,is broadenedro include groups ofindividuals of any one kind o[ organism.Likewise,cornmunity, in rhe ecologicalsense(sometimes deslgnatedas "biotic community"), includes all the populations occupying a given area. The community and the nonliving environment function together as an eco_ logical systemor ecosyst€m. Biocoenosis (lireralt, ..lfe and Earth andbiogeocoenosis

6

C HAPTER 1

The Scope of Ecology

Figure 1.4. Comparedwiththe strongset-pointcontrols at the organismlevelandbelow,organization andlunctionat the populationleveland aboveare muchlesstightlyregulated,with morepulsingand chaoticbehavio(but theyare controllednevertheless by allernatingpositiveand negative feedback-inotherwords,they exhibithomeorhesrs as opposedto homeostasls. Failureto recognize thisdifferencein cyberneticshas resultedin muchconfusionaboutthe balanceof nature.

Ecosphere

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Biomes

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t t Communities t Populations t OFGANISM Ecosystems

No sefpointcontrols (+ and -) feedback maantaanjng pulsingstates withinlimits HOMEORHESIS

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functioning together"),terms frequentlyusedin Europeanand Russianlirerarure,are roughly equivalent to community and ecosystem,respectively.Refe[ing again to Figure 1-3, the next level in the ecologicalhierarchy is the landscape,a term originally referring to a painting and defined as "an expanseof sceneryseenby the eyeas one view" (M€rridm-Webster's Colleglo.te Dictionary,lOth edition, s.v."landscape").ln ecology,landscape is defrnedas a "heterogenousarea composedo[ a cluster of interactingecosystemsthat are repeatedin a similar manner throughout" (Forman and Godron 1986). A wctershedis a convenientlandscapeJevelunit for large-scalestudy and managementbecauseit usually has identifiable natural boundaries. Biomeis a term in wide use for a largeregionalor subcontinentalsystemcharacterizedby a major vegetationt)?e or other identifying landscapeaspect,as, for example,the Temperate Deciduous Forestbiome or the Continental Shelf Oceanbiome. A reglonis a large geologicalor political area that may contain more than one biome-for example, the regionsof the Midwest, the AppalachianMountains, or the PacificCoast. The largestand most nearly self-sufficientbiological sysremis ofren designatedasrhe ecosphere, which includes all the living organismsof Earth interacting with the physicalenvironmentasa whole to maintain a self-adjusting,looselycontrolledpulsing state(more about the concept of "pulsing state"Iater in this chapter). Hierarchicaltheory providesa convenientframework for subdividing and examining complex situationsor extensivegradients,but it is more thanjust a useful rankorder classification.lt is a holistic approachto understandingand dealingwith com-

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SECTION 3

The Emergent property principte

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piex siruations,and is an alternativeto the reductionist approachof seekrnganswers by reducing problems ro lower-levelanalysis(Ahl and Allen 1996). More than 50 yearsago,Novikoff (1945) poirued out that rhereis both continuity and discontinuity in the evolurion of the universe.Developmentmay be viewed as continuous becauseit involvesnever-endingchange,but it is also drsconLtnuous becauseit passesrhrough a seriesof different levelsof orqanizarion.As we shall dis_ cussin Chapter 3, the organizedstateo[ Ii[e is mainraineJ by a conrinuousbut srepwise flow ofenergy. Thus, dividing a gradedseries,or hierarchy,into componentsis in many casesarbitrary, but sometimessubdivisionscan be basedon natural discon_ tinuities. Becauseeach level in the levels-of-organization spectrum is ,.integrated"or interdependentwith other levels,there can be no sharp lines or breaksin a functional sense,nor even betweenorganismand population. The individual organism,for ex_ ample, survive for long without its population, any more than the organ -cannot would be able [o survive for long as a self-perpetuaringunit without its organlsm. Similarly, the community cannot exist wirhour rhe cyclinq of materialsand the flow of energyin rhe ecosysrem.This argumenris applicablet"orhe previously discussed mistaken notion that human civilization can exist separatelyfrom the natural world. It is very rmporrantto emphasizethar hierarchiesin natureare nested-Lharts, each level is made up of groups of lower-level unirs (populations are composedof groups of organisms,for example). ln sharp contrast,human-organizedhierarchies rn Sovernments,cooperations,univercities,or the military are nonnested(sergeants are not composedofgroups ofprivates, for example).Accordingly,human-organized hierarchiestend ro be more rigid and more sharply separatedii compared ro natu_ ral levelso[ organization.For more on hierarchrcaltheory, seeT. F. H. Allen and Starr (1982),O'Neill et al. (1986),and Ahl and Allen (1996).

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3 TheEmergent Propefi Principte Al important consequenceof hierarchical organization is that as componems, or subsets,are combined to produce larger functional wholes, new propenies emerge that were not preseni at the level below Accordingly, an emergent property of in ecologicallevel or unit cannot be predicted from the study of the componentsof that level or unit. Another way to expressrhe sameconcept rs nonreducibie propenythat is, a property ofthe whole not reducibleto the sum ofrhe propeniesof the parts. Though findings at any one level aid in the study of the next level, they never com_ pletely explain the phenomenaoccurring ar the nexr level,which musr itselfbe studied to complete rhe picrure. Two examples,one from the physical realm and one from rhe ecologicalrealm, will sufficeto illusrrate emergentproperries.When hydrogen and oxygen are combined in a certain molecular configuration, water is formed-a liquid wirh properties utterly different from those of its gaseouscomponents.When certain algaeand coelenterateanimals evolvetogetherto produce a coral, an efficientnutrientiycling mechanismis createdthat enablesthe comblned system to maintain a high rate of productivity in watercwith a very low nutrient content. Thus, the fabulousproduc-

8

CHAPTER 1

The Scope of Ecology

tivity and diversity of coral reefsare emergentpropenies only at the level of the reef community. Salt (1979) suggestedthat a distinction be made betweenemergempropeties, as defined previously,and collective properties, which are summationsof the behavior of components.Both are propertiesof the whole, but the collectivepropertiesdo not lnvolve new or unique characteristicsresuking from the functioning of the whole lniL Birth rateis an exampleof a population level collectiveproperty, as it is merely a sum of the individual births in a designaiedtime period, expressedas a lraction or percentof the total number of individuals in the population. New propertiesemerge becausethe componentsinteract, not becausethe basic nature of the componentsis changed.Partsare not "melted down," as it were, but integratedto produce unique new properties. lt can be demonstratedmathematicallythat integrativehierarchies evolvemore rapidly from their constituentsthan nonhierarchicalsystemswith the same number of elements;they are also more resilient in responseto disturbance. Theoretically,when hierarchiesare decomposedto theirvarious levelsoIsubsysrems, the latter can still interac[ and reorganizeto achievea higher level of complexity. Someattributes,obviously,becomemore complex and variableas one proceeds to higher levelsof organization,but often other attributesbecomelesscomplex and lessvariableas one goesfrom the smaller to the larger unit. Becausefeedbackmechanisms(checksand balances,forcesand counterforces)operatethroughout, the amplitude ol oscillations tends to be reduced as smaller units function within larger units. Statistically,the va ance of the whole system level property is less than the sum of the varianceof the parts. For example,the rate of photosynthesisof a foresr community is lessvariablethan that of individual leavesor treeswithin the community, becausewhen one component siows down, another component may speedup to compensate.When one considersboth the emergentpropenies and the increasing homeostasisthat develop at each level, not all component parts must be known before the whole can be understood.This is an important point, becausesome contend that it is uselessto try to work on complex populations and communitieswhen the smaller units are not yet fully understood. Quite the contrary, one may begin study at any point in the spectrum, provided that adjacentlevels, as well as the level in question,are considered,because,as alreadynoted, some attributes are predictable from parts (collectiveproperties),but others are no[ (emergentproperties).ldeally, a system-levelstudyis itselfa threefoldhierarchy:system,subsystem(next levelbelow), and suprasystem(nextlevelabove).Formore on emergenlproperties,seef. F. H. AIIen and Starr(1982),T. F. H. Allen and Hoekstra(1992),and Ahl and Allen (1996). Each biosystemlevel has emergentproperties and reduced varianceas well as a summation of attributes of its subsystemcomponents.The folk wisdom about the forest being more than just a collection of treesis, indeed, a first working principle of ecology.Although the philosophy of sciencehas alwaysbeenholistic in seekingto understandphenomenaasa whole, in recentyearsthe practiceof sciencehasbecome increasinglyreductionist in seekingto understand phenomenaby detailed study of smallerand smaller componenls.LaszLoand Margenau(1972) describedwithin the history o[ sciencean alternation of reductionist and hoiistic thinking (redi{ctiorxism constructionism and atomism-holism are other pairs of words used to contrast these philosophicalapproaches).The law of diminishing retums may very well be involved here, as excessiveellort in any one direction eventuallynecessitates taking the other (or another) direction. The reductionistapproachthat hasdominatedscienceand technologysincelsaac

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Transcending Functions and Control Processes 9

Newton hasmade major contdbutions. For example,researchat the cellular and molecular levelshas establisheda firm basis for the future cure and prevention of cancersat the level of the organism.However,celllevel sciencewiil contribute very little to the well-being or survival of human civilization if we understandthe higher levels of organization so inadequatelythat we can hnd no solutions to population overgrowth, pollution, and other forms ofsocietal and environmentaldisorders.Both holism and reductionism must be accordedequal value-and simultaneously,not altematively (E. P Odum 1977; Barrett 1994). Ecologyseek slnthesis, not separation. The revival of the holistic disciplinesmay be due at leastpartly to citizen dissatisfaction with the specializedscientistwho cannot respond to the large-scaleproblems that need urgent attention. (Histodan L),nn White's 1980 essay"The Ecology of Our Science"is recommendedreadlng on this viewpoint.) Accordingly, we shall discuss ecologicalprinciples at the ecosystemlevel, with appropiate attention to organism, population, and community subsetsand to landscape,biome, and ecospheresuprasets.This is the philosophical basisfor the organizationo[ the chaptersin this book. Fortunately,in the past I0 years,technologicaladvanceshaveallowed humans to deal quantitativelywith large,complex systemssuch as ecosystemsand landscapes. Tracer methodology,masschemistry (spectrometry,colorimetry, chromatography), remotesensing,automadcmonitoring, mathematicmodeling, geographicalinformation systems(GlS), and computer technologyare providing the tools. Technologyis, of course,a double-edgedsword: it can be the means of underctandingthe wholenessof humans and nature or of destroyingit.

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4 Transcending Functionsand ContrulProeesses Whereaseachlevel in the ecologicalhierarchy can be expectedto haveunique emergent and collectiveprope ies, there arc basic functions that operateat a]l levels.Examplesof such transcending functions are behavior,development,diversity, energetics,evolution, integration,and regulation (seeFig. l-3 for details).Someo[these (energetics,for example)operatethe samethroughout the hierarchy,but others differ in modusoperandiat differentlevels.Natural selectionevolulion, for example,involvesmutations and other direct geneticinteractionsat the organismlevel but indlrect coevolutionaryand group selectionprocessesat higher levels. It is especiallyimpoftant to emphasizethat although positive and negativefeedback controls are universal,from the organismdom, control is sel?oirlf,in that it involvesvery exactinggenetic,hormonal, and neural controls on growth and development, Ieadingto what is often called homeostasis. As noted on the right-hand side of Figure 1-4, there are no set-pointcontrolsabovethe organismlevel (no chemostats or thermostatsin nature). Accordingly, feedbackcontrol is much looser,resulting in pulsing rather than sieady states.The term homeorhesis, from the Greek meaning "maintaining the floq" has been suggestedfor this pulsing control. ln other words, there are no equilibriums at the ecosystemand ecospherelevels,but there arepulsing bclances,such asbetweenproduction and respirationor betweenoxygenand carbon (the scidioxide in the atmosphere.Failure to recognizethis differencein cybernetics encedealingwith mechanismsof control or regulation)has resultedin much confusion about the realitiesof the so-called"balanceof nature."

10 CHAPTER1

TheScopeot Ecology

5 Ecologicallnterfacing Becauseecology is a broad, muLtileveldiscipline, it inrerfaceswell with lraditional disciplinesthat tend to have more narrow focus. During the past decade,there has been a rapid rise of interfacefields of study accompaniedby new societies,journals, symposium volumes, books-and new careers.Ecological economics,one of the most important, was mentionedin the frrst sectionin this chapter.Others that are receiving a greatdeal oI attention,especiallyin resourcemanagement,are agroecology, biodiversity,conservationecology,ecologlcalengineering,ecosystemhealth, ecotoxicology,environmentalerhics,and restorationecology. In the beginning, an interface effort enriches the disciplines being interfaced. Lines of communication are established,and the experliseo[ narrowly trained "experts" in each field is expanded.However, for an interfacefield ro becomea new discipline, somethingnew hasto emerge,such asa new conceptor technology.The concept oInonmarket goodsand services,for example,was a new concept that emerged in ecologicaleconomics,but that inidally neither rraditional ecologistsnor economists would put in their textbook (Daily 1997; Mooney and Ehrlich 1997). Throughout lhis book, we will reler to natural capital and economiccapital. Natural capital is defined as the benefits and servicessupplied to human societiesby natural ecosystems,or provided "free of cosf'by unmanagednatural systems.These benehtsand servicesinclude purificadon oI water and air by natural processes,decomposition of wastes,maintenanceof biodiversity, control of insect pests,pollination o[ crops, mitigation of floods, and provision o[ natural beauty and recreation, amongothers(Daily 1997). Economic capital is defined as the goods and servicesprovided by humankind, or the human workforce, tlpically expressedas the gross national product (GNP). Gross national product is the total monetary value o[ all goods and serl,rcesprovided in a country during one year. Natural capital is typically quantifred and expressedin units of energy,whereaseconomic capital is expressedin monetary units (Table 1-1). Only in recent years has there been an attempt to value the world's ecosystemservicesand natural capital in moneury terms. Costanza,d'Arge, et al. (1997) estimatedthis value to be in the rangeof 16 to 54 trillion U.S.dollarsper year for rhe enrire biosphere,with an averageof 33 triliion U.S. dollars per year. Thus it is wise to protect natural ecosystems,both ecologicallyand economically,becauseof the benehtsand servicesthey provide to human societies,aswill be illustrated in the chantersthat follow.

6 AboutModels Ifecology is to be discussedat the ecosystemlevel, for reasonsalreadyindicated,how can this complex and formidable systemlevel be dealt with? We begn by describing simplifred versionsthat encompassonly the most important, or basic,propertiesand functions. Because,in science,simplified versionsof the real world are called models, it is appropriatenow to introduce this concept. A model (by definition) is a formulation that mimics a real-world phenomenon

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S E C T I O N6

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AboutModels 11

and by which predictionscan be made.ln their simplestlorm, modelsmay be verbal or graphic (infotmal). Ultimately, however, models musr be sraristicaland mathematical Uormdl) i[ their quantitative predictions are ro be reasonablygood. For example, a mathematicalformulation that mimics numerical changesin a population of insectsand that predicts the numben in the population at some time would b€ considereda biologically useful model. lf the insectpopulation in questionis a pest species,the model could have an economicallyimportant application. Computer-simulatedmodelspermit one to predict probableoutcomesasparametersin the model are changed,as new parametersare added, or as old on€s are removed. Thus, a mathematicalformulation can often be "tuned" or refined by computer operations to improve the "nC'to the real-world phenomenon. Above all, models summarizewhat is understood about the situation modeled and therebydelimit aspectsneedingnew or better data, or new principles. When a model does not work-when it poorly mimics the real world-computer operadonscan often provide cluesto the refinemenmor changesneeded.Once a model proves to be a useful mimic, opponunities for experimentationare unlimited, becauseone can introduce new factorsor perturbationsand seehow they would affectthe system.Even when a model inadequatelymimics the real world, which is often the casein its early stages of development,it remainsan exceedinglyuseful teachingand researchtool if it revealskey componentsand interactionsthat merit specialattention. Contrary to the feelingof many who are skepticalabout modeling the complexity of nature, information about only a relativelysmall number ofvariables is ofren a sufficient basisfor effectlvemodels becausekey factors,or emergentand orher imegrative properties,as discussedin Sections2 and 3, often dominate or control a large percentageofthe action.Watt (1963), for example,stated,"We do not needa rremendous amount o[ information about a great many variablesto build revealingmathe matical models."Though the mathematicalaspectsof modeling are a subject for advancedtexts,we should review the first stepsin model building. Modeling usually beginswith the construction of a diagram, or "graphic model," which is often a box or companmenLdiagram,as illustrated in Figure 1-5. Shown are two properties, P1and P2,that interact, I, to produce or alfect a third prope y, P], when the systemis driven by an energysource,E. Five flow pathways,F, are shown, with F1 representingthe input and F6 the output for the systemas a whole. Thus, at a minimum, there are five ingredientsor componentsfor a working model of an ecologrcalsituation, namely,(l) an energ) sourceor other outside forcing function, E; (2) propertiescalled state variables, P1,Pr, . . . P"; (3) flow pathways, Fr, F2, . . . Fi, showing where energyflows or material transfersconnectpropertieswith each other and with forces;(4) interaction functions, I, where forcesand propertiesinteract to modify, amplify, or control llows or createnew "emergenC'properties;and (5) feedback loops, L. Figure 1-5 could serveas a model for the production of photochemicalsmog in the air over Los Angeles.ln this case,P1could representhydrocarbonsand P2nitrogen oxides,two products of automobileexhaustemission.Under the driving force of sunlight energy,E, rheseinteract to produce photochemicalsmog, P1.In this case, the interaction function, l, is a slrrergisticor augmentativeone, in that P3is a more seriouspollutant for humans than is P1or P2acting alone. Alternatively,Figure 1-5 could depict a grasslandecosystemin which P1representsthe greenplanE that convet the energyof the Sun, E, to food. P2might representa herbivorousanimal that eatsplants, and P:lan omnivorous animal that can eat

1 2 C H A P T E R]

The Scope of Ecology

Figure 1-5. Compartment diagramshowingthefjvebasjccomponents of primaryInterestrn modelingecological systems. E : energysource(forcingfunction);pj, p2,p3= statevariables; F1-F6= flow pathways; | : interaction function;L = feedbacklooo.

eitherthe herbivores or rhe plants.ln rhiscase,the interactionfunction,I, could representseveralpossibilities. Ir could be a no_preference swirchi[ observntron in the realwotld showecL that the omnivorep, eatseitherpr or pr, accordingto availability. Or I could be specifiedto be a constantpercentage valuei[ it wasfound that rhe dier o[ P, rvascomposeclof, say, 80 percent plant and 20 percent animal narrer, rrre_ specrivco[ the srateo[ p, or pr. Or I cou]d be a seasonai switchi[ pr feedson plants during one part of the yearancLon animalsduring anorherseason.Or I could be a thresholdswitch il P, greatlyprelcrsanimalfood and switchesto plantsonly when P, is rcducedto a low level. Fccclbcrch loopsare imporLant learuresoI ecologicalmodels becausethey repre_ sentcontrolmechanisms. Figure l-6 is a simplilieddiagramoIa systemth fearures a feedbackloop in which "downstream,, ourput,or so;e part o[ ii. is fed backor .e cycleciro affector perhapsconrrol"upstream., .o.pon.nrs. For exrmple,the feed_ back loop could representpredalion by 'downsrream',organisms,C, that reduceand thereby rend to control the grouth o[,,upstream,'herbivoresor plants B and A in the fooclchain. Often. such a feedbackacruallypromotesthe growth or survivalof a downstrcamcol]tponent,such as a grazerenhancingfhe growth of plants (a .,reward feedback." asit rvere).

Figure 1-6. Compartmentmodelwith afeedbackorcontrol loop that transformsa linear system into a partiallycyclical one.

Feedback loop

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SECTI0N 6

AboutModels 13

Figute 1.7. Interactionof positive and negativefeedbacksin the relationships of atmosphericCOr, climate andcarbonse' warming,soilrespiration, questration(modifiedafter Luo et al. 2001).

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re'lt5 la c'n

Negative

Figure 1-6 could also representa desirableeconomicsystemin which resources, A, are convertedinto useful goods and services,B, with the production ofwastes,C, that are recycledand used again in the conversionprocess(A --+ B), thus reducing the waste output of the system.By and large, natural ecosystemshave a circular or loop design mther than a linear structure. Feedbackand cybernetics,the scienceof controls, are discussedin detail in Chapter 2. Figure 1-7 illustrateshow positive and negativefeedbackcan interact in the relationship betweenatmosphericCO2concentrationand climatic warminS. An increase in CO2 has a positive greenhouseeffect on global warming and on plant growth. However,the soil systemacclimatesto the warming, so soil resPirationdoesnot continue to increasewith warming. This acclimation results in a negativefeedbackon carbon sequestrationin the soil, thus reducing emissionof CO2 to the atmosphere, accordingto a study by Luo et al. (2001). Compartment models are greatly enhancedby 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 energylanguage(H. T. Odum and E. P Odum 1982; H. T. Odum 1996) are depicted as used in this book. ln Figure l-9, theses).tnbolsare used in a model of a pine lorest located in Florida. Also, in this diagram estimatesof the amount of energ'yflow through the units are shown as indicators of the relativeimportanceof unit functions. ln summary, good model definition should include three dimensions: (I) the spaceto be considered(how the system is bounded); (2) the subsystems(components)judged to be important in overall function; and (3) the lime interval to be considered. Once an ecosystem,ecological situation, or problem has been properly dehnedand bounded, a testablehlpothesis or serieso[ hlpotheses is developedthat can be rejectedor accepted,at leasttentatively,pending further expedmenLationor analysis.For more on ecologicalmodeling, seePattenand Jorgensen(1995), H. T. Odum and E. C. Odum (2000), and Gundersonand Holling (2002). ln the following chapten, the paragraphsheadedby the word statement are, in effect,"word" models of the ecologicalprinciple in question.ln many cases,graphic models are also presented,and in some cases,simplified mathematical formulations are included. Most ofall, this book attemptsto provide the principles, concepts,

14 CHAPTER 1 The Scope of Ecology

Energy circuit (A pathwayor flowof energy)

Energy source (Sourceol energyfrom outsidethesystem)

Consumer (Usesproducer energy for self-maintenance)

-\

t--_r -Y ----\.

-.L --:

Heatsink (Degradedenergy afterusein work)

Producer (Converts and concentrates sorarener9yl

Y

t-

Slorage {A compartmentoJ energy storage)

=

-v-*

$.-.,.4\--

lnteraclron (Twoor moreflows of energyto producea high-quality energy)

Capitaltransaction (Fow of moneyto payfor flowof energy)

Figule 1-8, TheH. T.Odumenergylanguagesymbolsusedin modeldiagramsin this book.

Figure 1-9. Ecosystemmodel using energylanguagesymbolsand including estimatedratesof energyflowfor a Florida pineforest(courtesyof H. T. Odum).

Heatsink(usedenergy)

-

SECIION 7

DisciplinaryReductionismto Transdisciptinary Hotism 1O

simplifications,and absrractionsthat one must deducefrom the realworld beforeone can understand and deal with situations and problems or construct marhematical models of rhem.

7 llisciplinarylieductionismto Tlansdisciptinary Holism a gaper entltled "The Emergenceof Ecologr as a New lmegrarive Discipline,,, ln E. P Odum (1977) noted that ecologyhad becomea new holistii discipline, having roots in the biologicai, physical,and social sciences,rather than jusr a iubdiscipline ofbiology. Thus, a goal of ecoiogyis to link the natural and sociaisciences.It should be noted that most disciplinesand disciplinary approachesare basedon increased specializationin isolation (Fig. l-10). The early evoiution and developmentofecol_

Figure 1.10. Progression ol relationsamongdisciplines fromdiscjplinary reductionism to transdisciplinary holism(afterJantsch 1972). )k.

E

DISCIPLINARY specialzingin isolation

tI

MULTIDISCIPLINARY no cooperation

CROSSDISCIPLINARY rigid polarizationtoward specific monodisciplinary concepl

INTERDISCIPLINARY coordination by higher levelconcept

TRANSDISCIPLINARY multi-levelcoordinationof entire education/ innovation systern

16 CHAPTER 1

The Scope of Ecology

: "many"), espeogli was frcquently basedon multidisciplinary approaches(multi cially during the 1960s and 1970s.Unfonunately, the multidisciplinary approaches lacked cooperation or focus. To achievecooperation and define goals,insliutes or centerswere establishedon campusesthroughout the world' such as the lnstilute of Ecologylocatedon the campusof lhe University ofGeorgla Thesecrossdisciplinary uppro".h", (ctott = "traverse":Fig. 1-10) frequently resultedin polarization toward a specificmonodisciplinary concept,a poorly funded administrativeunit, or a narrow mission. A crossdisciplinaryapproachalso frequently resultedin polarized facuhy reward systems.Institutions of higher leaming, traditiona\ built on disciplinary structures, have diffrculties in administering programs and addressi.ngenvironmental problemsaswell astaking advantageofopponunities at greatertemporal and spatial scales. = "among') were To addressthe dilemma, interdisciPlinary approaches(inter employed,resultingin cooperationon a higher-levelconcept,problem, or question' t'oi example, the process and study of natural ecological successionprovided a higher-level concept resulting in the successof the SavannahRiver Ecological Labotheorized that new systemProperratory (SREL)during its conception.Researchers and that it is theseproperdevelopment of ecosystem the course during ties emerge that occur (E P Odum form changes growth and for species account ties that largely approachesare cominterdisciplinary Today, for details). 8 1969,1977, seeChapter global levels' and landscape, at ecosystem, problems mon when addressing problems, need to solve increased is an There however. be done, Much remainsto manin a transdisciplinary resources manage literacy, and promote environmental innovation and educalion entire involves approach large-scale ner. This multilevel, systems(Fig. I-10). Thil integrativeapproach to the need for unlocking cause-and#ect explanations across and among disciplines (achieving a transdisciplinary understanding) has been termed consilience(E. O Wilson 1998), sustainability scien'e (Barrett2001) Actually, the continued de(Kateset al. 2O0l), and integrativescietLce (the "study of the household"or''place where we velopmentofthe scienceofecology science of the future This integrative much-needed into that live';) will likely evolve and approachesto principles, concepts, knowledge' book attempts to provide the process learning and underpin this educationalneed