Nordic Society Oikos Organisms as Ecosystem Engineers Author(s): Clive G. Jones, John H. Lawton and Moshe Shachak Reviewed work(s): Source: Oikos, Vol. 69, No. 3 (Apr., 1994), pp. 373-386 Published by: Wiley on behalf of Nordic Society Oikos Stable URL: http://www.jstor.org/stable/3545850 . Accessed: 11/02/2013 12:21 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]. Wiley and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos. http://www.jstor.org This content downloaded on Mon, 11 Feb 2013 12:21:08 PM All use subject to JSTOR Terms and Conditions OIKOS 69: 373-386.Copenhagen 1994 Organismsas ecosystemengineers Clive G. Jones,John H. Lawton and Moshe Shachak Jones,C. G.,Lawton, J. H. andShachak, M. 1994.Organisms as ecosystemengineers. - Oikos 69: 373-386. Ecosystemengineers are organisms that directly or indirectly modulate the availability of resourcesto otherspecies, by causingphysical state changes in bioticor abiotic materials.In so doingthey modify, maintain and create habitats. Autogenic engineers (e.g. corals,or trees)change the environment via theirown physical structures (i.e. theirliving and dead tissues). Allogenic engineers (e.g. woodpeckers, beavers) change theenvironment bytransforming living or non-living materials from one physical state to another,via mechanicalor othermeans. The directprovision of resources to other species,in theform of livingor dead tissuesis notengineering. Organisms act as engineerswhen they modulate the supplyof a resourceor resourcesother than themselves.We recognise and define five types of engineering and provide examples. Humansare allogenicengineers par excellence,and also mimicthe behaviour of autogenicengineers, for example by constructingglasshouses. We explorerelated conceptsincluding the notions of extendedphenotypes and keystone species. Some (but not all) productsof ecosystemengineering are extendedphenotypes. Many (perhapsmost) impacts of keystone species include not only trophic effects, but also engineersand engineering. Engineers differ in theirimpacts. The biggesteffects are attributabletospecies with large per capita impacts, living at high densities, over large areasfor a long time,giving rise to structuresthat persist for millennia and that modulatemany resource flows (e.g. mimamounds created by fossorial rodents). The ephemeralnests constructed by small,passerine birds lie at theopposite end of this continuum.We provide a tentativeresearch agenda for an explorationof the phenom- enonof organismsas ecosystemengineers, and suggestthat all habitatson earth support,and are influenced by, ecosystem engineers. Jones,C. G., Inst.of Ecosystem Studies (IES), BoxAB, Millbrook,NY 12545, USA. - J. H. Lawton,NERC Centrefor Population Biology,Imperial College, Silwood Park, Ascot,Berks, UK, SL5 7PY,and IES. - M. Shachak,Mitrani Centerfor Desert Ecology, Blaustein Inst. for Desert Research, Ben-Gurion Univ. of the Negev, Sede Boqer 84900, Israel, and IES. Interactionsbetween organisms are a majordeterminant common. The ecological literature is rich in examplesof of the distributionand abundanceof species.Ecology habitatmodification by organisms,some of whichhave textbooks(e.g. Ricklefs1984, Krebs 1985, Begon et al. beenextensively studied (e.g. Thayer 1979, Naiman et al. 1990) summarisethese important interactions as intra- 1988).However, in general,population and community and inter-specificcompetition for abiotic and bioticre- ecologyhave neitherdefined nor systematically identi- sources,predation, parasitism and mutualism.Conspic- fiedand studied the role of organisms in thecreation and uouslylacking from the list of key processes in most text maintenanceof habitats.There is noteven a word,or booksis therole that many organisms play in thecre- words,in commonuse to describethe process. We will ation,modification and maintenanceof habitats.These call the process EcosystemEngineering and the orga- activitiesdo notinvolve direct trophic interactions be- nismsresponsible Ecosystem Engineers. tweenspecies, but they are neverthelessimportant and Beaver(Castor canadensis) are familiarexamples of Accepted21 September1993 Copyright(? OIKOS 1994 ISSN 0030-1299 Printedin Denmark- all rightsreserved OIKOS 69:3 (1994) 373 This content downloaded on Mon, 11 Feb 2013 12:21:08 PM All use subject to JSTOR Terms and Conditions organismsacting as ecosystemengineers. By cutting impactsof engineerson communitiesand ecosystems. treesand using them to construct dams they alter hydrol- We areinterested solely in discoveringproperties that all ogy,creating wetlands that may persistfor centuries. engineershave in common.We addressthe scale and "Theseactivities retain sediments and organic matter in magnitudeof theireffects later. the channel,... modifynutrient cycling and decomposi- tiondynamics, modify the structure and dynamics of the riparianzone, influence the character of water and mate- rials transporteddownstream, and ultimatelyinfluence plantand animal community composition and diversity" Classificationof organisms as engineers (Naimanet al. 1988). Table1 summarisesexamples of organisms as ecosystem However,beaver are by no meansthe only ecosystem engineers.The table is illustrative,not exhaustive. Addi- engineers.As we willshow, a vastarray of specieshave tionalexamples are discussed at greater length in the text. effectsthat are fundamentallysimilar, albeit often on All theexamples of whichwe are awarecan be as- moremodest spatial and temporal scales. Yet there is no signedto one of fivepossible cases (Fig. 1), or to a commonlanguage to describewhat ecosystem engineers combinationof twoor moreof these cases. As in many do, no formalstructure to modeltheir effects, and no otherareas of ecology,the diversity of biologicalpro- generaltheory round which to organiseunderstanding of cesses meansthat precise pigeon-holing is sometimes theprocess. Examples, which are developedmore for- difficult.The boundariesbetween types of engineering mallybelow (for others, see Table 1), includenot only areoccasionally fuzzy and, in thereal world, separating beaverand their dams but also gophers,ants and termites engineeringfrom other ecological processes may also be thatmove soil, woodpeckersthat drill holes, alligators difficult,simply because these non-trophic interactions thatmake wallows, rock-eating snails, trees, corals, sea- alwaysco-occur with trophic interactions. We discuss grassbeds and Sphagnum blanket bogs. some difficultcases as we proceed.The majorityof The purposesof thisarticle are fourfold: (i) to define examplesare, however, easy to classify.The legendto andto giveexamples of ecosystem engineering by orga- Fig. 1 explainsthe conventional notation used to describe nisms;(ii) to developa conceptualframework that ex- them.For clarity, itis easiestto introducethe arguments plainsand classifiesits effects; (iii) to showhow orga- usingbeaver and their dams. nismalengineering differs from related concepts (e.g. Beaverconform to case 4 in Fig. 1. Thatis theyare 'keystonespecies' Paine 1969,Krebs 1985); (iv) andto allogenicengineers, taking materials in theenvironment identifyquestions for further work on organismsas eco- (in thiscase trees,but in themore general case it can be systemengineers. First we definewhat we meanby an anyliving or non-living material), and turning them (en- ecosystemengineer, before providing examples and a gineeringthem) from physical state 1 (livingtrees) into conceptualframework for what is, andis not,ecosystem physicalstate 2 (deadtrees in a beaverdam). This act of engineering. engineeringthen creates a pond,and it is thepond which hasprofound effects on a wholeseries of resource-flows usedby other organisms. The critical step in thisprocess is thetransformation oftrees from state 1 (living)to state 2 (a dam).This transformation modulates the supply of Definitions otherresources, particularly water, but also sediments, Ecosystemengineers are organismsthat directly or in- nutrientsetc. A criticalcharacteristic ofecosystem engi- directlymodulate the availability of resources (other than neeringis thatit mustchange the availability (quality, themselves)to otherspecies, by causingphysical state quantity,distribution) ofresources utilised by other taxa, changesin bioticor abioticmaterials. In so doingthey excludingthe biomass provided directly by thepopula- modify,maintain and/or create habitats. tionof allogenicengineers. Engineering is not the direct The directprovision of resourcesby an organismto provisionof resources in the form of meat, fruits, leaves, otherspecies, in theform of living or dead tissues is not orcorpses. Beaver are not the direct providers of water, in engineering.Rather, it is thestuff of most contemporary the way that prey are a directresource for predators, or ecologicalresearch, for example plant-herbivore orpred- leavesare food for caterpillars. ator-preyinteractions, food web studiesand decomposi- Now considerthe autogenicequivalents of beaver tionprocesses. (Fig. 1, case 3). Simpleexamples are thegrowth of a Autogenicengineers change the environment via