Estimatesofminimumviablepopulationsizesforvertebratesand factors influencing those estimates DavidH.Reed a, *,JulianJ.O’Grady a ,BarryW.Brook b , Jonathan D. Ballou c , Richard Frankham a a Key Centre for Biodiversity and Bioresources, Department of Biological Sciences, Macquarie University, NSW, 2109, Australia b Key Centre for Tropical Wildlife Management, Northern Territory University, Darwin, NT, 0909, Australia c Department of Conservation Biology, Conservation and Research Center, National Zoological Park, Smithsonian Institution, Washington, DC 20008, USA Received 2 March 2002; received in revised form 10 October 2002; accepted 1 November 2002 Abstract Populationsizeisamajordeterminantofextinctionrisk.However,controversyremainsastohowlargepopulationsneedtobe toensurepersistence.Itisgenerallybelievedthatminimumviablepopulationsizes(MVPs)wouldbehighlyspecific,dependingon the environmental and life history characteristics of the species. We used population viability analysis to estimate MVPs for 102 species. We define a minimum viable population size as one with a 99% probability of persistence for 40 generations. The models are comprehensive and include age-structure, catastrophes, demographic stochasticity, environmental stochasticity, and inbreeding depression. The mean and median estimates of MVP were 7316 and 5816 adults, respectively. This is slightly larger than, but in generalagreementwith,previousestimatesofMVP.MVPsdidnotdiffersignificantlyamongmajortaxa,orwithlatitudeortrophic level, but were negatively correlated with population growth rate and positively correlated with the length of the study used to parameterize the model. A doubling of study duration increased the estimated MVP by approximately 67%. The increase in extinction risk is associated with greater temporal variation in population size for models built from longer data sets. Short-term studies consistently underestimate the true variances for demographic parameters in populations. Thus, the lack of long-term studies for endangered species leads to widespread underestimation of extinction risk. The results of our simulations suggest that conservation programs, for wild populations, need to be designed to conserve habitat capable of supporting approximately 7000 adultvertebratesinordertoensurelong-termpersistence. # 2003ElsevierScienceLtd.Allrightsreserved. Keywords: Demographicstochasticity;Endangeredspecies;Extinction;Minimumviablepopulationsize;Populationvariability;Populationviability analysis 1. Introduction The Earth is currently suffering a catastrophic loss of biodiversity (Lawton and May, 1995). A primary goal ofconservationbiologyistoarrestthisloss.Population size has been shown to be the major determinant of persistenceinpopulationsofavarietyofanimalspecies (Brown, 1971; Jones and Diamond, 1976; Toft and Schoener, 1983; Diamond et al., 1987; Newmark, 1987; Pimm et al., 1988, 1993; Richman et al., 1988; Soule´ et al. 1988; Berger, 1990; Kindvall and Ahle´n, 1992; Schoener and Spiller, 1992; Rosenzweig, 1995; Foufo- poulos and Ives, 1999). As the catastrophic loss of bio- diversity continues unabated, guidelines for how extinction risk is related to population size should be a high priority in conservation biology (Shaffer et al., 2000). Population viability analysis (PVA) provides a quan- titative means for predicting the probability of extinc- tion and for prioritizing conservation needs (Shaffer, 1981; Gilpin and Soule´ 1986; Beissinger and Westphal, 1998).PVAcantakeintoaccountthecombinedimpacts of stochastic factors (demographic, environmental and genetic stochasticity) and deterministic factors (e.g. 0006-3207/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. PII:S0006-3207(02)00346-4 Biological Conservation 113 (2003) 23–34 www.elsevier.com/locate/biocon * Corresponding author at present address: Department of Biol- ogy, The University of Mississippi, PO Box 1848, University, MS 38677-1848, USA.