Nordic Society Oikos

On Ecological Fitting Author(s): D. H. Janzen Source: Oikos, Vol. 45, Fasc. 3 (Dec., 1985), pp. 308-310 Published by: Wiley on behalf of Nordic Society Oikos Stable URL: http://www.jstor.org/stable/3565565 . Accessed: 13/09/2013 19:33

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This content downloaded from 169.237.66.239 on Fri, 13 Sep 2013 19:33:00 PM All use subject to JSTOR Terms and Conditions OIKOS 45: 308-310.Copenhagen 1985

Dan Janzen'sthoughts from the tropics1 On ecologicalfitting

I've grownup on a dietof Darwin,Wallace and their occupiedby specieswith the following cyclical pattern culturaloffspring. But I'm facedwith the reality of the to theirhistories. Furthermore, these species are in the biologyof 100 km2of lowlanddry forest (Santa Rosa evolutionarilyquiescent stage in thecycle during their NationalPark) in northwestern Costa Rica. Someof my occupancyof the region.Initially, a speciesis a small backgrounddoes notprepare me for this: almost all the populationoccupying a small area. Sucha restrictedoc- ecologyI see aroundme couldquite easily come to be cupationoccurs through foundling establishment, habi- withvirtually no evolutionhaving occurred at Santa tat fragmentation,habitat shrinkage, etc. This popu- Rosa. lation evolutionarilypasses througha successionof Santa Rosa is a veryordinary place. The fine-scale genotypes.This change occurs because the habitat occu- mosaicof habitatsranges from 30-m-tall nearly ever- piedchanges and becausethe small population is being greenforest to 2-m-talldeciduous thorn scrub, with a evolutionarilyfine-tuned by selectionto theparticular varietyof anthropogenicsuccessional seres. There is a traitsof the habitatit occupies.Then, the population 0-350 m elevationrange, 900-2300 mm annualpre- abruptlyexpands out of its local habitat in theduration cipitation,and twodry seasons, one ofwhich is about6 ofa fewgenerations. The expansionoccurs because the monthslong and usually rain-free. Santa Rosa's habitats evolvingpopulation happens upon some genotype that are quite literallycrawling with complex biotic inter- is serendipitouslyrobust with respect to thechallenges actions.The participantsnumber at least650 species of ofliving throughout some large geographic area. It may plants,3100 species of Lepidoptera, 200-plus species of also occurbecause some geographic barrier has been re- seed-predatorbeetles, 58 speciesof mammals, 250-plus laxed(or bypassed),or becausemajor abiotic changes speciesof birds, and many more. It's decidedly tropical. makea smallhabitat into a widespreadone. The species The problemis thatat least98 percentof thesespe- is now widespread.By virtueof being huge, wide- cieshave geographic ranges covering tens of degrees of spread,on an adaptivepeak, and subject to a multitude latitude.While the majorityare commonand wide- of selectivepressures that are fine-scaleheterogeneous spreadin the dryNeotropics, another majority ranges andcontradictory, the species now becomes evolutiona- widelyover low elevationrainforest habitats as well. rilystatic. It is onlylikely to evolutionarilychange when Over theirwide ranges, these species interact in many a newgenotype appears that raises throughout complicatedways with many other species that do not muchof the species'range. It thencontinues to be a occurat SantaRosa. However,these wide-ranging spe- widespreadspecies until some sortof majorperturba- cies are madeup ofsimilar, if not apparently identical, tionoccurs throughout its range,whereupon it is ex- individualsin quitedifferent parts of theirranges. tinguishedor reducedto somesmall population that is The implicationsof these observations are difficultto againevolutionarily labile. Likewise, during its tenure reconcilewith the commonplaceview of a speciesas as a widespreadspecies, isolates occur from time to evolutionarilylabile. This difficulty leads me to wonder time,and a veryminute fraction of these start the cycle ifa profitableexcursion in evolutionaryecology might again. be to explicitlyintroduce some heterogeneityinto the It appearsto me thatSanta Rosa is almostentirely abilityof natural selection to moldgenomes. As I write occupiedby species with such cyclical histories and that that,I suddenlyrealize that I have blunderedthrough theyare occupyingthe site during the widespread phase thefront door of the turmoil over punctuated equilibria. of theirhistories. Furthermore, it appears to me that We don'thave to dig at the fossilrecord; punctuated mostcontinental habitats are occupied as is SantaRosa. equilibriaare righthere in frontof us, representedby Whensuch a speciesbreaks out of its local status mostof thespecies that you and I haveanything to do somewhereand arrivesat a site such as Santa Rosa, with. whathappens? Think in termsof Africanizedhoney I am hereconcerned with any region that is primarily bees,cattle egrets, feral cattle and guanacaste trees (or

308 OIKOS 45:3 (1985)

This content downloaded from 169.237.66.239 on Fri, 13 Sep 2013 19:33:00 PM All use subject to JSTOR Terms and Conditions gypsymoths, ring-neckedpheasants, feral house cats sures are sufficientlysimilar to maintain this single and kudzu). It willcome to occupysome, but not all the . habitatsat the site. If it is a plant,its flowerswill be pol- 2) The phenotypeis evolutionarilyfrozen and the linated to various degrees and qualities in different mothoccurs wherever its realized fitness is greatenough habitats.Likewise, its seeds willbe dispersedto various for persistence. In some habitats, the eye spots are degrees and into various patternsof seed shadows, highlyfunctional in deterringpredators, but the mothis whichwill in turnimpinge upon a wide varietyof habi- absentbecause its larvalhost plants are absent. In some tats. Only some of these habitatswill containmembers habitats,the eye spots and the behaviourof displaying of theplant population. Its foliagewill be fedon to vari- themsimply lead to increasedpredation by (too) smart ous degrees in differenthabitats and its fitnesswill be predators,but the mothremains a commonmember of variouslyreduced in these differenthabitats as a conse- the fauna because there are massive amountsof para- quence. Of the habitatsit occupies, in some it will be sitoid-freehost plants. In some habitats,the eye spots verycommon and breed, in some it willbe less common are highlyfuntional and thatis whythe mothis present. and breed, and in othersit willbe presentonly as strays Finally,in some habitatsthe eye spotsare simplyirrele- (be they adults or juveniles). These various levels of vant because thereare no significantvisually-orienting habitatoccupation will also be generatedby the more predators,but the mothis onlyoccasionally present be- traditionallyconsidered variations in physicalenviron- cause only in some years is there enough rain for the ment and impact of other plants. If an animal, all the host plant's seeds to germinate.So, when a mutantap- above kinds of interactionswill occur, and with the pears thatmodifies the eye spot so as to raise the moth's same consequences. In short, our newcomer will be fitnessin but one of the many habitatsit occupies, it patchilydistributed, variably abundant, and have differ- seems reasonablethat it does not spread throughoutthe ent interactionswith different organisms in the various moth'srange. However, it also seems likelythat such a habitatsof the Park. mutantmight persist in some small isolate of Automeris No evolutionarychange was necessaryor likelyfor io occupyingonly one habitat. our invadingspecies to incorporateSanta Rosa into its If thisapproach is not all nonsense,then in determin- range,and to develop the heterogeneousmicrodistribu- ing the processes that lead to structurein habitatswe tion and microexpressionof its fitnessthat it now has. should concernourselves with the ecological outcomes Furthermore,there is no reason to expect that the es- of successiveintroductions into a habitat,as well as with tablishedresidents did anythingother than ecologically the evolutionaryadjustments among species. There is, readjustto thisact of ecological fitting.All imaginable then,a strongesoteric rationale for the study of habitats levels of readjustmentmay occur, from going extinct to richin introducedspecies. On the one hand, it is tempt- no response.Almost all thecomplex interactions now at ing to criticallynote thateasily 99 percentof the papers Santa Rosa maybe nothingmore than the consequences in esotericecological journals today deal with"native" of a long successionof ecological fittingsof one wide- animalsand plants. On the otherhand, easily the same rangingspecies afteranother. 99 percentapplies to widespreadorganisms in habitats While seeminglyinnocuous, trite and obvious, I have so modifiedby recenthumans that the organismsmight constructedan argumentthat roughlysuggests that a as well have been introduced.The rationalethat I pre- major part of the earth's surfacemay be occupied lar- senthere also givesvery special meaningto the studyof gelyby organismsthat are richin ecologicalinteractions the natural historyof small, local or otherwiseevo- and have virtuallyno detailed evolutionaryhistory with lutionarilylabile populations. What gives a species its one another. In such a view, questions such as "What traits,what makes it "successful",may have little or are the selectivepressures maintaining such and such a nothingto do withits evolutionaryhistory while it is a set of traitsof an organism"would need to be severely widespreadspecies. augmented by "What mighthave been the selective There are two quite differentways that a habitatmay pressures that invented such a set of traits", "What come to have its traits. For example, does an extra- blocks theirdecay", and "What are the ecological pro- tropicalhabitat accumulatea set of caterpillarspecies cesses that lead to such and such a kind of ecological thatfeed primarilyin the springand autumnbecause 1) fit"? the species thatare therehave been selected to feed at Santa Rosa is occupied by a medium-sizedsaturniid thattime by the traitsof the plantsand the carnivoresat moth with hind wings bearing brightly-coloredlarge thosetimes of year,or 2) as species afterspecies arrived eye-likespots (Automerisio). This moth ranges from at thathabitat over the past, those thatpersisted were Canada to Costa Rica and has virtuallyidentical adults those that had the rightstuff for those times of year, over thisrange. Whichis the more reasonable explana- while those thatfailed were species thathad mid-sum- tion of these false eye spots? mer caterpillarsand life is miserablefor mid-summer 1) Througha rangeof 40 degreesof latitude,in habi- caterpillars?Are some of the plant species at Santa tatsranging from Illinois roadside ditches to a Costa Ri- Rosa quite free of herbivorybecause here, as well as can forestthat contains 200-plus species of visually-ori- throughoutthe rest of their ranges, they have evo- entingvertebrate potential predators, the selective pres- lutionarilyrepulsed each species of herbivorethat found

OIKOS 45:3 (1985) 309

This content downloaded from 169.237.66.239 on Fri, 13 Sep 2013 19:33:00 PM All use subject to JSTOR Terms and Conditions theplant? Or, is it thatsuch a plantevolved some par- 6) Whatare thedecay rates of traits in natureonce a ticularilyeffective deterrent when it was a local popu- speciesbecomes widespread, and whatinternal as well lation somewhereand then spread with this trait as externalprocesses determine the heterogeneityof throughoutits contemporary wide range? Is an ostenta- thoserates (i.e., to whatdegree does the phenotype tioustoxic butterfly the color here at SantaRosa thatis preventdecay of thegenotype)? bestfor advertisement to thepredators here? Or is it 7) Whatare the properties of serendipitous multipur- simplythat particular bright color because its phenotype pose traits(e.g., whatecological processes could con- workedwell somewhere,and workswell enoughfor verta non-migratoryspecies into a migratoryspecies, persistenceat SantaRosa despitethe fact that some mu- ratherthan asking how did migratorytraits evolve)? tantmight well have a higherfitness at SantaRosa? 8) How do all thosespecies get packed into tropical I predictthat there are somelarge and fruitfulsur- habitatswithout eating each other up or squashingeach prisesto comeout of questionssuch as other(as opposedto "howdid all those species evolve in the 1) Whatproperties should the arrayof speciesin a tropics")? habitat ifall arrived withtheir 9) Whatsorts of habitatsshould be particularilyim- display sequentially per- in offlots of and sonaltraits evolutionarily frozen, and then simply made portant spinning widespreadspecies, it to some whatsorts of habitats should primarily accumulate and degree? maintainlocal How does one betweenmultispecies species? 2) distinguish Whatare the detailed events that an mutualismsthat evolved vis a vis the ,and 10) actuallystop those thatare the consequenceof ecologicalfitting invadingwidespread species? (e.g., introduceagoutis to Africa,and thendetermine The complexinteractions enacted by introduced spe- howthe resultantmutualisms differ from those in the cies of animalsand plantsall overthe tropics make it homelandsof Neotropicalagoutis)? quiteclear that a speciesdoes nothave to evolvein a 3) What were the intensiveinteractions in small habitatin orderto participatein theinteractions in that populationsthat produced the salient traits of the large habitat.Widespread species are not adaptedto their numberof widespread species that we studytoday? habitats,they just are. In fact,it can evenbe argued 4) Whatwill be theconsequences of arbitrarily chop- thatmost members of most widespread species are quite pingout a smallblock of terrainoccupied almost en- maladaptedto theirhabitats. As anyoneknows who has tirelyby widespreadspecies and overnightconverting suffered a setbackin life,you don'thave to be well- themto localspecies (the biological history of almost all adaptedto survive.You justhave to survive.We are all NationalParks and Reservesaround the world)? asymmetricalpegs in squareholes. 5) Can we considerthe chemicaldefense traits of plantsas simplyone moretrait that leads to persistence ofthe plant in a -richhabitat, rather than as a traitselectively maintained by all thoseherbivores that do notfeed on theplant (i.e., whenleaf-cutting ants are introducedto Africa,the resultantfood choices they D. H. Janzen,Dept of Biology, Univ. of Pennsylvania, Phila- displaywill certainly not be coevolved)? delphia,PA 19104,USA.

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