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Biological Consequences of Ecosystem Fragmentation: a Review Author(S): Denis A Society for Conservation Biology Biological Consequences of Ecosystem Fragmentation: A Review Author(s): Denis A. Saunders, Richard J. Hobbs and Chris R. Margules Reviewed work(s): Source: Conservation Biology, Vol. 5, No. 1 (Mar., 1991), pp. 18-32 Published by: Wiley-Blackwell for Society for Conservation Biology Stable URL: http://www.jstor.org/stable/2386335 . Accessed: 11/10/2012 13:03 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-Blackwell and Society for Conservation Biology are collaborating with JSTOR to digitize, preserve and extend access to Conservation Biology. http://www.jstor.org Review BiologicalConsequences of Ecosystem Fragmentation:A Review DENIS A. SAUNDERS CSIRO Division of Wildlifeand Ecology LMB 4 P.O. Midland WesternAustralia 6056, Australia RICHARDJ. HOBBS CSIRO Divisionof Wildlifeand Ecology LMB 4 P.O. Midland WesternAustralia 6056, Australia CHRIS R. MARGULES CSIRO Divisionof Wildlifeand Ecology P.O. Box 84 Lyneham AustralianCapital Territory2602, Australia Abstract: Research on fragmentedecosystems has focused Resumen: La investigacionsobre los ecosistemasfragmen- mostlyon thebiogeographic consequences of thecreation of tados se ha enfocado principalmente en las consecuencias habitat "islands" of differentsizes, and has provided littleof biogeograficasde la creacion de "islas" de habitat de difer- practical value to managers.However, ecosystem fragmen- entestamaniosy ha sido de muypoco valorpracticopara los tation causes large changes in thephysical environmentas manejadores del recurso.Como quiera que sea la fragmen- well as biogeographicchanges. Fragmentation generally re- tacion de los ecosistemascausa grandes cambios en el medio sults in a landscape thatconsists of remnantareas of native ambiente fisico asi como en el ambito biogeografico.La vegetationsurrounded by a matrixof agriculturalor other fragmentacionresulta generalmente en terrenosque consis- developed land. As a result,fluxes of radiation; momentum ten de areas remanentesde vegetacion nativa rodeada de (i.e., wind), water,and nutrientsacross the landscape are una matriz de tierrasagricolas u otrasformas de uso de la altered significantly.These in turn can have importantin- tierra Como un resultado de esto, el flujo de la radiacion; fluences on thebiota withinremnant areas, especiallyat or del momentum(ej. el viento),del agua y de los nutrientesa near theedge betweenthe remnant and thesurrounding ma- travesde la tierrason alterados significativamente.Esto en trix. The isolation of remnant areas by clearing also has su turno,puede influenciare la biota dentro de las areas importantconsequences for the biota These consequences remanentes,especialmente en o cerca de los limitesentre los varywith the timesince isolation; distancefrom otherrem- remanentesy la matriz que los rodea El aislamiento de las nants, and degreeof connectivitywith otherremnants. The areas remanentesporla tala tambien tieneimportantes con- influencesof physical and biogeographicchanges are mod- secuenciaspara la biotay estas consecuencias varian con, el ified by the size, shape, and position in the landscape of tiempodesde el momentodel aislamiento, la distancia hasta individual remnants,with larger remnants being less ad- los otros remanentesy el grado de coneccion entreellos. La verselyaffected by thefragmentation process. The dynamics influencia de los cambios fisicos y biogeograficoses modi- ficada por el tamanio,la formay la posicion en el terrenode remanentesindividuales siendo los remanentesgrandes los menos afectados adversamantepor el proceso de fragmen- Paper submittedMay 1990; revisedmanuscript accepted 2, Septem- tacion. La dinamica de las areas remanentesson dirigidas ber 20, 1990. 18 ConservationBiology Volume 5, No. 1, March 1991 Saunderset al. ConsequencesofFragnentation 19 of remnantareas are predominantlydriven by factors aris- predominantementepor factores que surgen en el terreno ing in the surroundinglandscape. Management of, and re- circundante.El manejoy la investigacionde los ecosistemas search on, fragmented ecosystemsshould be directed at fragmentadosdeberi'a de dirigirsetanto al entendimientoy understandingand controllingthese external influencesas control de estas influencias externascomo a las biotas re- much as at the biota of theremnants themselves. There is a manentesen si. Hay unafuerte necesidadpara el desarrollo strongneed to develop an integratedapproach to landscape de un enfoque integradoen el manejo de tierrasque coloca managementthatplaces conservationreserves in thecontext a las reservaspara la conservacionen el contextodel terreno of the overall landscape. en general. Introduction the originalvegetation has been removed (Saunders et al. 1987a). Remnantsoften have been called habitatis- Since the developmentof agriculture,the naturalvege- lands and the changes thatresult from the isolationof tationcover of every continentexcept Antarcticahas these islandshave been the subject of considerablede- been extensivelymodified. A cycle of agriculturalde- bate in the literature.This debate has centeredmostly velopmentfollowed by overexploitationof the land has on the equilibriumtheory of islandbiogeography (Mac- been repeated throughoutrecorded history.Forman Arthur& Wilson 1963, 1967) and its applicabilityto (1987) quotes Plato's(ca. 2350 BP) descriptionof how conservation. In particular,the importance of size, an area ofancient Greece was strippedof its soil follow- shape,and designof single reserves and reservesystems, ing clearingand grazing,leaving "the mere skeletonof extinctionand colonizationrates, and species-arearela- theland." Overexploitation and theuse ofinappropriate tionshipshave been much discussed (Wilson & Willis agriculturalpractices have led to desertencroachment, 1975; Diamond 1975, 1976; May 1975; Terborgh1976; as in the Sahel region in NorthAfrica (Le Houerou & Whitcombet al. 1976; Simberloff& Abele 1976a4 1982; Gillet 1986; Ehrlich& Ehrlich1987), and to extensive Pickett& Thompson 1978; Game 1980; Marguleset al. loss of soil, oftenwith disastrousand dramaticconse- 1982; Boecklen & Gotelli 1984). Particularattention quences, as in the Dust Bowl of the UnitedStates (Hud- has been paid to the question of whetherone large re- son 1981). serve could preserve more species than several small The process of land clearingand the consequent en- reservesadding up to the equivalentarea of the larger vironmentaldegradation is continuingrapidly in many reserve(the so-calledSLOSS, or "singlelarge or several regionssuch as SoutheastAsia and SouthAmerica, par- small" debate; Simberloff& Abele 1976b, 1984; Gilpin ticularlyin areas of tropicalrain forest(Myers 1988). & Diamond 1980; Higgs & Usher 1980; Jairvinen1982; Australiaprovides an example of recentagricultural de- Willis 1984). velopment,with vast areas being cleared over the last These questionshave been reviewedelsewhere (Sim- 100 yearsfor cereal croppingand stockgrazing (Saun- berloff1988) and are not examinedin detailhere. While ders & Hobbs 1989; Hobbs & Hopkins 1990; Saunders of theoreticalinterest, most of these issues are of little et al. 1990). In some regions over 93% of the native practicalvalue in managingfragmented systems (Zim- vegetationhas been removedand the agriculturalland merman & Bierragaard1986; Margules 1987; Hobbs that has replaced it is subject to extensivewind and 1988; Margules& Stein 1989). The species-areaequa- water erosion or soil salinization,with consequentpol- tion,for example, may give a managera rough idea of lutionof water suppliesfor drinking and irrigation. how manyspecies will be maintainedon a remnantof a One legacy of the extensiveremoval of nativevege- given area, but will yield absolutelyno informationon tationis thatthe remainingvegetation is usuallyin frag- the practicalissue ofwhich habitatscontribute most to mentedpatches across the landscape.These patches or species richnessor on which species are most likelyto remnantsare situatedin differentpositions in the land- be lostfrom the remnant. Simberloff ( 1986) stated,"It is scape and on differentsoil types,possess differentveg- also sad thatunwarranted focus on the supposed lessons etationtypes, and varyin theirsize, shape, isolation, and of island biogeographytheory has detractedfrom the typeof ownership.Over much of the world,conserva- maintask of refugeplanners, determining what habitats tionof regional biotas depends entirely on theretention are importantand how to maintainthem." Margules and managementof these remnants.Conservation man- (1986), in a discussionabout two conservationevalua- agersare thereforefaced with the dual issuesof whether tion exercises,notes that,"no panel membersin either the remnantshave any practical conservationvalues, exercise consideredthe species-arearelationship or the and ifthey do, of how theymust be managedto retain equilibriumtheory of islandbiogeography in theireval- these values (Saunders et al. 1987a). uations;at least not explicitly."In addition,the debates In thispaper we use the word remnantto defineany about reservedesign and SLOSS are of limitedrelevance patch of nativevegetation
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