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The University of Chicago Competition Theory, Hypothesis-Testing, and Other Community Ecological Buzzwords Author(s): Daniel Simberloff Source: The American Naturalist, Vol. 122, No. 5, A Round Table on Research in Ecology and Evolutionary Biology (Nov., 1983), pp. 626-635 Published by: The University of Chicago Press for The American Society of Naturalists Stable URL: http://www.jstor.org/stable/2460845 . Accessed: 11/12/2014 15:31 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. . The University of Chicago Press, The American Society of Naturalists, The University of Chicago are collaborating with JSTOR to digitize, preserve and extend access to The American Naturalist. http://www.jstor.org This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions Vol. 122, No. 5 The AmericanNaturalist November 1983 COMPETITION THEORY, HYPOTHESIS-TESTING, AND OTHER COMMUNITY ECOLOGICAL BUZZWORDS DANIEL SIMBERLOFF Departmentof Biological Science, Florida State University,Tallahassee, Florida 32306 SubmittedOctober 12, 1982; Accepted April 19, 1983 Roughgarden's (1983) and Quinn and Dunham's (1983) thoughtfulessays on how to do communityecological research both fall into two parts: (1) general discussions of the meritsor lack thereofof various philosophicalstances toward communityinvestigation;and (2) technicalcriticismsof research,includingmuch of my own work, guided by philosophicalviews that theyfindpoorly suited to communityecology. Accordingly,my response will be in two corresponding sections. PHILOSOPHY Roughgardenbelieves thatan investigatorestablishesa factin sciencejust as in everydaylife, "by buildinga convincingcase forthe fact" (p. 583), throughhis native abilities, common sense, and experience. In everydaylife, he feels, we rarelyif ever adhere to formalrules in constructinga convincingcase, so it is rarelyifever appropriateforscientiststo abide by formalrules. I am sympathetic to Roughgarden's desire to ignore the entire corpus of epistemologyand the philosophyof science. Afterall, so much formalwritingby philosophersseems tedious, contrived,and supercilious."Every philosophy... is liable to degenerate in such a way that its problems become practicallyindistinguishablefrom pseudoproblems, and its cant, accordingly,practically indistinguishablefrom meaninglessbabble" (Popper 1963, p. 7). Further,as Roughgardenimplies,we seem to get along quite well in everydaylifeby usingcommon sense and experience to constructa world view, so why not apply the same approach to our scientificendeavors and let tendentiousphilosophers argue about how many angels can dance on thehead of a pin? If onlyforthetimeand mentaleffortsaved, this is a temptingproposition. Unfortunately,it is probably an overly simplisticone as well. For example, using common sense, experience, and native abilities,millionshave builta convincingcase forthe existence of a deity,some of themproceedingvery systematicallyto thisconclusion (e.g., James 1902). Othershave concluded by the same methodthatno such being exists, while agnosticshave argued,equally commonsensically and (to themselves,at least) cogently,that there is no possibilityof Am. Nat. 1983. Vol. 122, pp. 626-635. ? 1983 by The Universityof Chicago. 0003-0147/83/2205-0005$02.00. All rightsreserved. 626 This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions COMPETITION THEORY AND TESTING HYPOTHESES 627 correctlyreachingeitherof theothertwo positions.Are scientistsdoomed to such impasses, or are thereformalproceduresthatpromisea more satisfactoryresolution? At least where experimentis possible, it seems to me that applicationof Popper's procedure (1963, 1972), clearly stated hypotheses and rigorous attemptedfalsification,is more likely to get us closer to an accurate account of Platt(1964) providesa nontechnicaldescriptionof nature,and to do so efficiently. how thisprocedure,whichhe terms"stronginference,"has spurreda remarkable series of successes in areas of physicsand molecularbiologyand argues thatit is the strictformalizationthatis responsible. Now it is truethatPopper's procedurecould well be partof a commonsensical constructionof a convincingcase, so the two approaches need not be viewed as mutuallyexclusive alternatives.It is equally truethatthe search forconfirmatory and is veryseductive.I suspect evidence is easier thanthe search forfalsification that in everyday experience it is by far a more common modus operandi than and I feelthatin communityecologyitalso holds sway. This attemptedrefutation, is the detrimentI see to rejectingformalizationin favorof commonsense. If one agrees that a procedure is effectiveand logically correct, its formalizationis simplyan aid to force us continuallyto match our actions and thoughtsto the procedure.An analogyto probabilitytheoryis apt here. Most people feelthatthey outcomesin have an intuitiveor commonsensenotionofthelikelihoodof different simple but well-framedquestions thatarise in everyday,life. A friendlygame of blackjack is likelyto be played, if not completelyintuitively,at least withlittle more system than recalling the preceding few cards played, and with some attentionto hunches. Yet we are very inclined to rely on formal statistical procedureswhen questions become more complex, even thoughthe procedures themselvesrelyon the same principlesthatwe ascribeto commonsense. Ifwe set out to make our livingby beatingthehouse consistentlyat blackjack,we would be muchmorelikelyto succeed ifwe rigorouslyemployeda countingprocedureand not the methodswe use at home. In exactly thisway, formalizationof scientific procedures in communityecology need not be antitheticto common sense, but oughtto help us to keep trackof what we have and have not establishedin our studyof what mustbe a vastlymorecomplicatedentitythanmolecularbiologists or blackjack players deal with. Also, if one agrees with me that confirmatory evidence per se is not verycompellingsince one can always findsome (Northrop in allocat1948; Popper 1963), formalizationoughtto help us to be more efficient ing our research time. It is ironic that Roughgardenshould call for adherence to common sense as opposed to the Popperian procedures that my colleagues and I have advocated while a numberof persons are contendingthat Popper's ideas have application well beyond the realms of naturalscience, includingday-to-dayactivity.The art criticGombrich(1960, 1973) and neurophysiologist Gregory(1973), forexample, suggestthatperceptionitselfis a tacitconstructionof a hypothesis,withimaginationand/orexperiencefillingin thosepartsof a perceptthathave notbeen directly establishedby the senses. Popper himself(1972) notedthispsychologicalvariant of his refutationprocedure. When a perceptualhypothesisis incorrect,it is an illusionthatcan mislead us in our everydayactions. Our sensationsof the world This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions 628 THE AMERICAN NATURALIST constantlyprovide data thatcan be used to assess the hypothesis.To the extent that we ignore conflictingdata and accept those data that tend to confirmour illusion,we are notthinkingefficiently and our everydayactionsare morelikelyto be misguided.There is nothingmysteriousabout this psychologicalmodel; it is simplymeantto show thatin everydaylifeas in science, "buildinga convincing case" by common sense and experienceis not a trivial,automaticallyefficacious matter.And in everydaylifeas in science, applicationof a falsification procedure is likelyto help. Hintikka (1969, 1975) suggests a "possible worlds" model of epistemology, whereinany quest for knowledge,be it in everydayor scientificaffairs,begins witha large numberof depictionsof reality(possible worlds), all consistentwith "facts" that we agree are "established." Any advance consists in eliminating some possible worlds,therebynarrowingthe scope ofpotentiallyvalid depictions. Such a model, whose similarityto Popper's prescriptionforscientificresearchis apparent, seems eminentlyreasonable to me and indicates what constitutesan efficientprocedure in science as in everyday life: one that invalidates a large numberof hithertopossible worlds. It also suggeststo me thata major pitfallin both everyday and scientificreasoningis failureto posit initiallya sufficiently large universe of possible worlds, so that the real world is not among those initiallypresent. Particularlywithrespectto evolutionarycommunityecology theory,I feel that the Popperianprescriptionshould be moderated,as Lakatos (1970) suggests,into a "sophisticated falsificationism."Afterall, the historyof science is rifewith observationsthat originallyseemed anomalous but in the lightof later developmentswere shownto be quite consistentwiththehypothesesthatspawned them. The complexityof communitiesand difficulty of manipulatingthemdictatethata theorynot be immediatelydiscardedbecause a singleobservationseems to refute it. As Lakatos (1970, p. 179) says, "one must treat budding programmesleniently,"especially while theyseem to be growingand generatingresearchthat anticipates new facts. But eventuallythere must be a willingnessto confront theorywithcontradictory data in a decisive manner;Lakatos (1970, p. 179) allows only that "a budding research programme . . . should be sheltered for a while . . . " (myitalics). My complaintis thatcommunitytheoryhas been shelteredfor longenoughand has littlemoreto show forthisforbearancethana proliferation of theory.This is not a novel concern (cf. McFadyen 1975; Smith 1976; Futuyma 1975; Brown 1981; Pielou 1981),and I do notmean to be dogmaticabout it. It may be, as Roughgardenfeels, thatwe are on thethresholdof dramatic,rigoroustests ofcommunitytheorythatwillfinallyprovidecommunityecologywithwell-tested, predictivemaxims.If so, thispast decade and a halfof intensetheoreticalactivity will have been well spent. If not, a large fractionof a generationof evolutionary ecologistswill have spentits timemanipulatingmodels thatare practicallyirrelevant to nature. Having statedmyreasons fordesiringsome sortoffalsification procedure,even ifdelayed, I findmuchin Roughgarden'sphilosophicalsectionwithwhichI agree. Roughgardenis correctto distinguishbetweenmathematicaland biologicalproofs in that, exactly as Lakatos emphasizes, subsequent observations can always This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions COMPETITION THEORY AND TESTING HYPOTHESES 629 change our interpretation of a physical observation;but as Lakatos argues, this condition dictates only patience and leniency, not eternal immunityfrom attemptedfalsification.I also agree withRoughgarden(cf. Simberloff1980) thatthe variedand complex natureof communitiespreventsa simple"litmustest" forthe historicoccurrence of coevolution or interspecificcompetition.Popper (1972, 1980) feels that his procedure applies to both singularand historicevents, but surelyfalsification is vastlymoredifficult withoutreplication.This difficulty in no way obviates theultimateattemptto refutea theory,however,and italso suggests monumentalmodestyin assessing the scope and value of a model. I even agree with Roughgardenand with Quinn and Dunham that we were incorrectto suggest (Strong et al. 1979) that the hypothesisof no population interactionshas "logical primacy" as a null hypothesis.I do feel, however,that such a hypothesisis an apt startingpoint. There is such a plethoraof information in the populationbiology literatureon the ecological and evolutionaryresponses of individualspecies to habitatvariationthatit seems reasonable to assume that the habitat must always affecta population's densitywhetheror not species interactionsare important.In fact, as an appeal to Occam's razor (admittedlya psychologicallyattractiveratherthan a logically necessary principle)it seems appropriateto ask if habitat variationmightnot explain a species' distribution withoutany need to invoke otherspecies' distributionsat all. If thiswere so, it would certainlynot demonstratethatspecies interactionsare not important,nor have my colleagues or I ever suggestedthatit would. But it shouldforceus to recognizethatour universeof "possible worlds" is largerthan we had thought.If, on the other hand, we reject this null hypothesis(as my colleagues and I have oftendone), we have successfullynarrowedthisuniverse. By contrast,approachingthismatteras a problemof everydaycircumstances,as Roughgardensuggests, seems oftento have led to no null hypothesisat all, in which instancewe cannot in principlehave narrowedthe universe. Othertimes, "common sense" has led to an initialuniversethatexcludes an eminentlyreasonable galaxy ofpossible worlds. Pielou (1981, p. 24) observes thattheoreticians modelingmultispeciessystemsroutinelyassume thatcompetitionis occurringand that such models ". . . shackle thought. With depressing frequency, they cause studentsto assertthatthisor thatprocess must(or cannot)be takingplace, merely because some model or othersays it must(or cannot). So-called counter-intuitive models have thedesirableeffectofjoltingthoughtout oftherutscreatedby earlier models .... ." I agree withRoughgarden,too, thatit is a distractionto focus moreon testinga model thanon testinghypothesesabout processes in an actual system. simplifying My question to him then is, How many of the pages on evolutionaryecology theoryin, for example, The American Naturalist, are misguidedlyfocused on theoryand how many are actually requiredto presentthe model thatmotivates testsof hypotheses?Roughgardenfeelsthatthemajorculpabilityfortheory'sbad press rests on the "always naive" and "usually incorrect" set of "popular impressionsabout 'what theoryactually does say' " (p. 598). I presumethatby "popular impressions" he refers to interpretationsby us benighted nonmathematiciansand by the nonecologistswho have to determinewhat practical This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions 630 THE AMERICAN NATURALIST lessons ecology yields.I would pointout firstthatthereis some blame attachingto the modelersthemselves(cf. Levin 1975) and second, thatthe bloated theoretical literaturehas consequences beyondbeinga chore forecologiststo wade through. Simplyby persistenceand volume alone, a fieldacquires both a lifeof its own and at least temporaryrespectabilityamongnonexperts.That ecological modeling forits own sake is now a recognizeddisciplineis witnessedby the emergenceof journals (e.g., Ecological Modeling, Theoretical Population Biology) devoted primarilyor solely to modelingand scarcely at all to whetherthe models correspond to nature. Now, I agree withRoughgardenthattheoreticaland empirical research need not march in lockstep; however, I would emphasize his qualifier: "Nonetheless, theoreticalecology is ultimatelyvalued by itsutilityin understandingecological processes in nature" (p. 597). I suspectthata good manyecological modelingattemptsare not motivatedby thisultimategoal. Pielou (1981) observes thatmany ecological models seem to have been constructedwithno purpose in mind,but I believe she overstatesthis case. No biological purpose perhaps, but some purpose nonetheless.One would surelynot go throughthe troubleof doing theresearch,writingthepaper, and attendingto thenumeroustediousdetailsthat ensureitspublicationifone onlywantedto fillup time.Many purposesin addition to biological ones may be served by doingsuch work: amourpropre,professional prominenceand its attendantrewards,even such mundanemattersas tenureand promotioncan all benefitfromdoingthiswork. Such goals are neitherblameworthynor unique to ecological modeling;Merton (1973) makes a strongcase that they motivateall scientists. The importantpoint is that such factors imparta tenacityto a disciplinesuch thatit withersslowlyeven when it turnsout to yield few substantiveresults. Alas, it is no easier for nonecologiststo assess the validityof an ecological school thanit is forecologists to judge the relativemeritsof different approaches to cosmology or cancer etiology. So long as its practitionershave academic credentials and are sufficiently adamant and vocal, a patina of respectability accrues to a school in the eyes of nonspecialists,even scientists.I would argue thatthe enhanced statureof ecology in the eyes of othersciences thatRoughgarden perceives (but does not document)is, ifit exists at all, not informedapprobationof ecology's accomplishments.More likely,it would be simplya comfortable feelingthatsome ecologists are speakingin the mathematicaltermsthatphysical scientistsunderstand,ratherthanin Latin nomina. "Physics-envy" (Cohen 1971) is misguided; ecologists' proper goal should be not approbationfromphysical scientistsbut a firmunderstanding of naturalprocesses, to thepointwherewe can predictthe outcome of specifiedecological processes and answer many of the specificecological questions of directapplicationthatcurrentlybesiege us. Respectabilityamong nonspecialistshas consequences beyond the enhancementof self-esteem,unfortunately. In the absence of a clear consensus among workersin the field,a recommendationsupposedlydictatedby "theory" can be promoted as policy when "theory" could as well be writtenor construed to generate exactly the opposite recommendation.For one example, the International Union for Conservation of Nature and Natural Resources (1980) in its overview statementabout what measures we mustimmediatelytake to stem an This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions COMPETITION THEORY AND TESTING HYPOTHESES 631 imminentdisastrous increase in extinctionrate, states thatrefugedesign criteria and managementpractices should accord with the equilibriumtheoryof island biogeography.This is in spite of the factsthat(a) the theoryitselfis increasingly viewed as not a particularlyfaithful respresentationof mostnature(Gilbert1981); (b) the main recommendationadvocated in the name of theory-single large refugesratherthan clusters of small ones-is not a consequence of the theory (Simberloffand Abele 1976; Higgs 1981); and (c) mostempiricaldata thatbear on thematterdo not supporttherecommendation(Simberloff and Abele 1982). Were thisrecommendationtakenseriously,it could reallyhinderconservationefforts.I could easily cite other examples in such practical areas as pest and disease control,food production,etc., whereecological modelshave been used to support prominentrecommendationsthat could as well be wrong as right.My point, however,is not to indicateweaknesses of specifictheoreticalrecommendations. Rather,I want to suggestthatexaggeratedclaims forecological models can have consequences in the real world. Finally, I must demurfromRoughgarden'sassertionthatthe Popperianphilosophical stance is moot and irrelevantto the practiceof scientificresearch. I can onlyhope thatmyabove discussionof thebenefitsof systematization and rigorin reasoningabout empiricalfacts, admittedlyas much an assertionas Roughgarden's advocacy of common sense, is the more cogent. Nor can I concurwithQuinn and Dunham that,effectiveas Popper's procedure is in some sciences, it is inappropriatein ecology and evolutionbecause the latter fieldsare characterizedby multiplecausality. I agree that any naturalhistoric phenomenonis very likely to have been affectedby a numberof forces, but I suspect that this complicationonly demands more ingenuityon the part of researchers in framingunambiguous hypotheses. Afterall, molecular biological processes are also affectedby a varietyof inputs,yet Quinn and Dunham do not contestPlatt's estimation(1964) of the success of stronginferencein thatfield. Many of the crowningachievementsof molecular biology were achieved in spite of complicated inputs, by clever experimentalprocedures that could unambiguouslytest well-chosenhypotheses.In geneticsit is routineto use mutantsthatcannotmanufacturea particularmoleculein orderto show an effectthat would otherwisebe masked. Averyet al. (1944) demonstratedthatDNA was the active agentin bacterialtransformation by usinga Pneumococcus strainthatdoes not manufacturea polysaccharidecoat. Benzer (1962) used mutantsof T4 phage, the rII types,thatcould not grow on strainK of Escherichia coli to demonstrate manyaspects of genetic structure.Many otherdefinitiveexperimentsin physiology and moleculargeneticsrestedon inhibiting or repressingagentsthataffected one or more molecular functionswhile leaving others intact. Analogous techniques should allow ecologiststo testhypothesesin similarlyincisivefashion.For example, at a stroke,Keith (1963) was able to refutethehypothesisthatsnowshoe hare cycles are part of an intrinsicpredator-prey oscillationwhen he foundthat hare populationsoscillate on AnticostiIsland, in the absence of lynx.Underwood (1978) caged three grazing gastropod species in a varietyof densities to show clearly competitiveeffectsof Cellana tramoserica on Bembicium nanum, and equally clearly the absence of othercompetitiveeffectsamong the species. For This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions 632 THE AMERICAN NATURALIST Underwood's resultas forKeith's the key to a clear resultwas an unequivocally simplified,by whatevermeans, to falsifiablehypothesisand a systemsufficiently allow an unambiguoustest of the hypothesis. It is not necessary, fora hypothesisto be falsifiable,thatit state thatforce A and only force A is acting,while the alternativehypothesisposits only force B. Rather,it is at least as much a matterof statingthe hypothesesand choosingthe tests in such a way that theiroutcome is unambiguous.It does not make sense (nor have mycolleagues or I attemptedthis) to hypothesizethatcompetitionand only competitionis responsiblefora communitypattern,and to pose as alternatives that predation and only predation, weather and only weather, etc., are task in communityecology to state uniquelyresponsible.It maybe a verydifficult informative hypothesesthatallow unambiguousanswers,but it is probablyworth theeffort(Strong1980). If the bone of contentionis some claimedhistoricor very infrequentlyoccurringphenomenonthe resolutionof the matterby Popperian methodswill be even harder,but I doubtthatthe inductiveor descriptivemethod advocated by Quinn and Dunham-estimating the probable contributionsof a numberof a priori"causes"-will provide an easier path. Such a methodseems to me to resembleRoughgarden'scommonsenseapproach, and would thus suffer the same shortcomings.As I said above, I could well be wrong,and only the collectivejudgmentof ecologists over the nextfew years will determineifeither variantproduces convincingand usefulecological descriptions. I cannotrefrainfromprotestingabout two pointsoffact.First,nowheredid we (or Popper or Lakatos, for that matter)argue that scientificprogresswill occur fasterifone investigatesalternativehypothesesratherthanthe principalthesisof interest. This view of procedure as an either/orphenomenon erects a false dichotomy.Our contentionhas been thattheremustbe morethanone hypothesis (nulland alternatives,ifyou will) such thattheempiricaldata soughtwillarguefor one over the others: the very proceduredescribed by Platt (1964) formolecular biology. Second, Quinn and Dunham state, "Popper (1959, but see 1983a, 1983b) argued explicitlythat estimates of probabilityare unfalsifiable,and thus not subjectto scientifictestundercriteriaof disproof" (1983, p. 603). Popper (1972, a of revision of 1959) states: "I believe that my emphasis upon the irrefutability probabilistic hypotheses . . . was healthy: it laid bare a problem which had not been discussed previously .... Yet my reform ... changes the situation entirely. For this reform . .. amounts to the adoption of a methodological rule . .. which makes probabilityhypothesesfalsifiable"(p. 191). TECHNICAL CRITIQUE As sympatheticas I am to Roughgarden'sdesire to obviate the philosophyof science, I cannot agree with much of his technicalcritique. A fairfractionof it seems to me to exemplifythe shortcomingsof a commonsensicalapproach. For example, Roughgarden'soutline of coevolutionarytheoryappears (by virtueof niches' beingto therightor leftofone another)to assume a one-dimensionalniche space, surelyan unwarrantedrestrictionon the numberof possible worlds. That one-dimensionalresults need not triviallyand automaticallytranslateinto mul- This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions COMPETITION THEORY AND TESTING HYPOTHESES 633 tidimensionalones is well known(e.g., May 1974). And nowherein his criticismof Connell's protocol does Roughgardensuggestany conceivable observationthat would be taken to indicate that exploitationcompetitionwas not importantin a particularsystem. Then why do any field or laboratoryresearch at all? It is certainlytruethatthe removalexperimentadvocated by Connell (1980) cannot in principleexorcise the ghost of competitionpast, but it seems as if no data can, even though we are not dealing here with a logical proof. At least Connell's procedurehas the virtueof clarifyinghow naturepresentlyoperates. Roughgardenagain seems to narrowtheuniverseof possible worldsunwarrantedly when he criticizesour nullhypothesesbecause "No biologicalprocesses are exhibitedthatproduce the distributionspredictedby [them]" (p. 591). Although we do not attemptto account foreveryforceactingon a species, norfortheexact mechanismby whichforcesact, it is clear thatwe are askingifspecies' individual responses to the physical environmentsufficeto explain their distributions. Roughgarden similarlyomits likely importantforces from his coevolutionary model. (Is he saying,e.g., thatweatheris unimportant, thatthehabitatis homogeneous?) He is also not yeryspecificabout mechanisms(e.g., is the competition exploitationor interference?).Generallyhe seems to be arguingthata model, to be useful,mustbe realistic;but he has not noticedthatall models are unrealistic by virtueof being abstractions(Simberloff1982); thatthe dividingline between "realistic" and "unrealistic" is subjective (Pielou 1981); and that unrealistic models are at least as useful as realisticones in advancingour understandingof natureor generatingmechanistichypotheses(Pielou 1981; Simberloff1982). In testingnull and alternativehypothesesbased on more or less unrealistic models, what is importantis that differentdegrees of realism not affectthe models' performancesin thearea of concern.Roughgardensubsequentlyseems to accept this view when he avers that most communityecology models aim to simplify,and that"we fillthe gaps in the simplifieddescriptionwithassumptions thatmay actuallybe false iftakenliterally,but whichare hoped somehow not to be too misleading" (p. 594). I do not see that Roughgarden's revolutionary models depict the "real processes thatbringspecies to islands" any more than ours do, yet he feels we mustmodel these forcesto determinewhat distributions of data are expected in the absence of interspecific competition.Whymusthe not also model themto determinewhat distributions are expected in the presence of interspecificcompetition? In no sense have my colleagues and I ever said the world is withoutstructure. Nor have we intendedthata patternmustbe manifestbeforeone is licensed to pursue research into what may have caused the pattern.Our sole concern has been thatthe fullrangeof forcespotentiallygeneratingthe patternbe recognized so thatthe search forits causes not be undulycircumscribedinitially.Certainlya process may be studiedfruitfully beforeits consequences are well understood,so long as the process does not imperceptibly become establishedas fact simplyby virtueof its studyor its mathematicaltidiness.Roughgardendoes not recognize thisas a problem: "Sometimes it is obvious thata process is occurring"(p. 592). No doubt as obvious as is the existence or nonexistenceof God. The "serious technical" criticismsof our work to whichRoughgardenalludes This content downloaded from 169.230.243.252 on Thu, 11 Dec 2014 15:31:41 PM All use subject to JSTOR Terms and Conditions 634 THE AMERICAN NATURALIST are fullydiscussed by Strongand Simberloff(1981), Simberloff(1982), and Connor and Simberloff(1983), who have shown themto be eitherincorrector of no consequence withrespect to our conclusions. Nor has Roughgardenstatistically substantiatedhis claim thatour testsare biased towardtypeII errors.I have yetto see his analysis of bias or power of any of his models or ours. Related complaints by Quinn and Dunham are similarlydismissedin the above rebuttals.In particular, the observationthata source pool may alreadybe structuredby competition was anticipatedby Connor and Simberloff(1979) and Stronget al. (1979), and is not germaneto the hypothesestheywere testing,nordoes it generatecircularity. Its sole potentiallydebilitatingeffectis to lower statisticalpower. Withrespectto presence and absence of species combinationson islands, Connorand Simberloff (1979) were explicitthatthe occurrencefrequenciesof the different species might well be partlydeterminedby interactions,but thatthe question asked was ifthe co-occurrencedistribution patternsofthedifferent species, above and beyondthe individualfrequencies,demanded an interactiveexplanation: ". . . unless one is willingto ascribe to competitionthe facts thatislands have different numbersof species and that species are found on differentnumbers of islands, the New Hebrides data still argue heavily against the claim that competitiondetermines of species on islands" (p. 1,136,myitalics). As for mostaspects ofthedistribution the contentionthatthe bill sizes in a species pool may already be structuredby competition,Stronget al. (1979) did not disputethis.All theydid was to perform the classical statisticalprocedure of randomization(Bradley 1968; Hendrickson in bill1981) to see ifobserved subsets of birdson islands were typicallydifferent size characteristicsfromthose we would have observed ifspecies and races were independentlyand randomlyplaced on islands. Again, we did not contend that sizes of birdsin the species pool were not affectedby competition;we asked only ifthe sizes of whicheverraces coexist, above and beyondthe distribution of sizes in the pool, additionallydemand an interactiveexplanation. LITERATURE CITED Avery,0. T., C. M. MacLeod, and M. McCarty. 1944.Studieson thechemicalnatureofthesubstance of pneumococcal types. Inductionof transformation inducingtransformation by a desoxyribonucleicacid fractionisolated fromPneumococcus type III. J. Exp. Med. 79:137-158. Benzer, S. 1962. The finestructureof the gene. Sci. Am. 206:70-84. Bradley,J. V. 1968. Distribution-free statisticaltests. 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