Chapter 9 Population Viability Analysis: Data Requirements and Essential Analyses The biological diversity of the earth is threatened by the burgeoning human population. To prevent extinctions of species, conservationists must manage many populations in isolated habitat parcels that are smaller than desirable. | Chapter 9 Population Viability Analysis Data Requirements and Essential Analyses Gary C. White The biological diversity of the earth is threatened by the burgeoning human population. To prevent extinctions of species conservationists must manage many populations in isolated habitat parcels that are smaller than desirable. An example is maintaining large-bodied predator populations in isolated limitedarea nature reserves Clark et al. 1996 . A population has been defined as a group of individuals of the same species occupying a defined area at the same time Hunter 1996 132 . The viability of a population is the probability that the population will persist for some specified time. Two procedures are commonly used for evaluating the viability of a population. Population viability analysis PVA is the method of estimating the probability that a population of a specified size will persist for a specified length of time. The minimum viable population MVP is the smallest population size that will persist some specified length of time with a specified probability. In the first case the probability of extinction is estimated whereas in the second the number of animals that is needed in the population to meet a specified probability of persistence is estimated. For a population that is expected to go extinct the time to extinction is the expected time the population will persist. Both PVA and MVP require a time horizon a specified but arbitrary time to which the probability of extinction pertains. Definitions and criteria for viability persistence and extinction are arbitrary such as a 95 percent probability of a population persisting for at least 100 years Boyce 1992 . Mace and Lande 1991 discussed criteria for extinction. Ginzburg et al. 1982 suggested the phrase quasi-extinction risk as the probability of a population dropping below some critical threshold a concept also Population Viability Analysis 289 promoted by Ludwig 1996a and Dennis et al. 1991 . Schneider and Yodzis
