What is population viability analysis (PVA) and what data does it typically require?

• A. Population viability analysis is a structured risk assessment of extinction probability under demographic and environmental stochasticity; requires life-history rates, population size, demographic variability, environmental scenarios.
• B. An assessment of predator-prey interactions; requires predator densities and prey growth rates.
• C. A census of all individuals in a population; requires only current population size.
• D. An analysis of genetic drift; requires only allele frequency data.

Answer: (C)

Population viability analysis is a modeling approach used to estimate the likelihood that a population will persist or go extinct over a future period, taking into account uncertainty. It explicitly incorporates randomness in survival and reproduction (demographic stochasticity) and variation in environmental conditions (environmental stochasticity), and it can include potential catastrophes or management actions. To run a PVA, you need data that describe how the population actually grows and changes over time: life-history rates such as age-specific survival and fecundity, current population size and the age or stage structure, and information on how these vital rates vary from year to year (demographic variability). You also specify possible future environments or scenarios—changes in habitat, climate, or other factors—and how the population responds to density, such as carrying capacity and density dependence. If relevant, you may include genetic considerations like inbreeding effects. With these inputs, the analysis runs many simulated futures to estimate extinction risk, expected time to extinction, and potential management outcomes. A simple census that only records current population size doesn’t capture how the population might change under different conditions or how variability in vital rates could affect viability, which is why PVA relies on more than just a snapshot.