Management of Small Populations: Concepts Affecting the Recovery of Endangered Species Author(s): Gary E. Belovsky, John A. Bissonette, Raymond D. Dueser, Thomas C. Edwards, Jr., Christopher M. Luecke, Mark E. Ritchie, Jennifer B. Slade and Frederic H. Wagner Source: Wildlife Society Bulletin (1973-2006), Vol. 22, No. 2 (Summer, 1994), pp. 307-316 Published by: Wiley on behalf of the Wildlife Society Stable URL: http://www.jstor.org/stable/3783262 Accessed: 24-02-2016 16:01 UTC REFERENCES Linked references are available on JSTOR for this article: http://www.jstor.org/stable/3783262?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. 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 Wildlife Society are collaborating with JSTOR to digitize, preserve and extend access to Wildlife Society Bulletin ( 1973-2006). http://www.jstor.org This content downloaded from 66.254.247.100 on Wed, 24 Feb 2016 16:01:40 UTC All use subject to JSTOR Terms and Conditions Wildl. Soc. Bull. 22:307-316, 1994 ""INMY OPINION . MANAGEMENTOF SMALL POPULATIONS:CONCEPTS AFFECTINGTHE RECOVERYOF ENDANGEREDSPECIES GARY E. BELOVSKY, ConservationBiology Program, Department of Fisheries and Wildlife and Ecology Center, Utah State University,Logan, UT 84322-5210 JOHN A. BISSONETTE, National Biological Survey,Utah Cooperative Fish and WildlifeResearch Unit and Conservation Biology Program, Department of Fisheries and Wildlife, Utah State University,Logan, UT 84322-5210 RAYMOND D. DUESER, ConservationBiology Program, Department of Fisheries and Wildlife, Utah State University,Logan, UT 84322-5210 THOMAS C. EDWARDS, JR., National Biological Survey, Utah Cooperative Fish and Wildlife Research Unit and ConservationBiology Program, Department of Fisheries and Wildlife,Utah State University,Logan, UT 84322-5210 CHRISTOPHER M. LUECKE, ConservationBiology Program, Department of Fisheries and Wild- life, Utah State University,Logan, UT 84322-5210 MARK E. RITCHIE, ConservationBiology Program, Department of Fisheries and Wildlife, Utah State University,Logan, UT 84322-5210 JENNIFER B. SLADE, Department of Fisheries and Wildlife, Utah State University,Logan, UT 84322-5210 FREDERIC H. WAGNER, ConservationBiology Program, Department of Fisheries and Wildlife and Ecology Center, Utah State University,Logan, UT 84322-5210 Key words: endangeredspecies, recovery plans, small populations Based on surveyresponses from state agen- ever,we wishto cautionthat the elimination cies, Hayes (1991) examinedwhich mamma- of the initialcauses of endangerment,such as lian orderswere mostvulnerable to becoming habitatdestruction, may not remove the threat endangered,threatened, or ofspecial concern, to populationsand may notbe theprime con- and the perceivedcauses. Habitatdestruction cernin developingrecovery plans. was listedmost frequently as the cause of a Wildlifebiologists should work to preserve species' vulnerability,whereas overexploita- and restorehabitat for plants and animals,as- tionwas onlyconsidered important for some sumingthat many populationsof plantsand Carnivoraand Artiodactyla.Reviews of ex- animalsare threatenedas a resultof habitat tinctionsthrough history have documented the lossand degradation.Unfortunately, although overridingsignificance of habitatdestruction the preservationof suitablehabitat is neces- (Hester 1967, Diamond 1984). Therefore, sary,it may no longerbe sufficientto ensure wildlifebiologists and conservationistshave the recoveryof smallpopulations because the long consideredhabitat destruction to be the appropriationof habitatand "lettingnature criticalinitial threat to plantand animalpop- takeits course" (i.e., managementby "benign ulations(Terborgh and Winter1980). How- neglect")may no longerbe sufficient;rather, This content downloaded from 66.254.247.100 on Wed, 24 Feb 2016 16:01:40 UTC All use subject to JSTOR Terms and Conditions 308 Wildl. Soc. Bull. 22(2) 1994 innovativeand activemanagement may be endangeredspecies and their extinction or re- needed.Especially when considering habitat coveryin NorthAmerica since European col- lossand degradation,we shouldinclude hu- onizationin the sixteenthcentury. Hester's man-inducedfactors, such as climatechange conclusionsparalleled those of Hayes' (1991) (e.g.,global warming) and habitatfragmen- survey of state agencies: habitat destruction has tation,as well as theelimination (e.g., gray been the major cause of endangerment,and wolf,Canis lupus, in theGreater Yellowstone overharvesting has been a secondarycause. Ecosystem)and introductionof species(e.g., However,we examinedthe traitsof endan- rainbowtrout, Oncorhynchus mykiss, into cut- geredspecies (and several subspecies, e.g., heath throattrout, 0. clarki,streams and lakes). hen [Tympanuchuscupido]) thathave either We and others(e.g., Ehrlich and Ehrlich survived(n = 34) to the present(still endan- 1981)fear that managers and agenciesmight geredor recovered) versus those that have gone become complacent,operating under the extinct(n = 34), as reportedby Hester(1967). premisethat the protection of a pieceof hab- Thesedata are crude,but simple statistical tests itat ensurespopulation persistence. Hayes' based on binomialestimates of the 95% con- (1991) surveysupports our concern,because fidenceintervals for percentages illustrate in- stateagencies never attributed population de- terestingcontrasts between the 2 groupsof spe- clinesto the special demography ofsmall pop- cies. Species names used as examplesfollow ulationsand onlyonce attributed declines to Hester's(1967) listingfor easy comparison. thespecial population genetics of smallpop- 1. ulations. Endangeredspecies that have survivedare representedby a greaterproportion of spe- Confusionbetween the initial causes of en- cies withlow reproductiverates (i.e., long dangermentand concernsfor the persistence generationtime, or small clutch or litter orrecovery of precarious populations was cau- size) thanthose that went extinct: 29% (15- tionedagainst by Ehrlich and Ehrlich(1981), 49%) versus3% (0-7%). For example,the becausethe causes for reduced populations may Haitianhutia (Plagiodontia hylaeum) with notbe thesame as thecauses for further de- its low reproductiverate survived,while clinesand possible extinction. Although recov- otherCaribbean island hutias with higher erycannot proceed without curtailing habitat reproductiverates went extinct (Geocapro- lossand degradation,once a populationbe- mys columbianus,G. ingrahami,Hexolo- comessmall its existence is threatenedeven bodon phenax, Isolobodon portoricensis, afterthe original causes of endangerment are and I. levir).Species with low reproductive controlled.The recovery or persistence ofsmall ratesoften are assumedto be morevulner- populationscannot occur without considering able to extinction,but thedata do thespecial demographic and genetictraits of notsup- port this. The observed smallpopulations. These considerations arethe opposite pattern mightbe explained if essenceof population viability analysis (Shaffer high reproductive ratescorrelate with high mortality rates (low 1987), interagencycooperation in manage- life then small ment(Salwasser et al. 1987),reserve design expectancy), populations (Diamond1986), and captivebreeding pro- mightbe moreprecarious, even though high grams(Thorne and Belitsky1989). reproductiverates permit populations to re- coverquickly (Belovsky 1987, Pimm 1991). Furthermore,high reproductive rates may HISTORICAL INSIGHTS produce populationsthat fluctuatemore Hester(1967) reviewedthe historicaland over time and periodicallyapproach very scientificliterature on mammalianand avian low numbers(Pimm 1991). This content downloaded from 66.254.247.100 on Wed, 24 Feb 2016 16:01:40 UTC All use subject to JSTOR Terms and Conditions IN MY OPINION ... * Belovskyet al. 309 2. Endangeredspecies that have survivedand theassociation between extinction and small thosethat have gone extinctdid not differ areais verystrong. Many of the extinct species in subjectiveestimates of theirpopulation (<30%) reportedby Hester(1967) were nat- densities(number/area) at the timeof Eu- urallyconfined to smallareas, especially is- ropeancontact: 44% (26-63%) versus41% lands,and consequentlymay have had small (23-60%) had low densities.For example, populations,but manybecame restricted to thesea mink(Mustela macrodon)a species smallareas that could only support small pop- witha high densitywent extinct, whereas ulationsthrough habitat destruction by hu- the marten(Martes americana) a species mans(e.g., the heath hen). Habitat destruction witha low densitysurvived. Low popula- canoccur by either a largeloss of habitat area tion densityoften is assumed to make a or by changingthe spatial distribution ofthe speciesvulnerable to extinction due to Allee habitat,i.e., fragmentation. In either case, small Effects(e.g., difficultiesin findingmates), populationsoften are created. butno evidencefor this emerged; however, Thenumber of species becoming threatened thismight not be expectedfor several rea- orextinct has increased over time (Fig. 1). As