Population Viability
Population viability is a term that refers to how vulnerable a population is to extinction in the relatively near future. The viability of a population is often presented as the probability of the species or population going extinct within a specified period of time.
Population Viability Analysis
Extinction probabilities are usually calculated using computer modeling in a process called Population Viability Analysis (PVA). Data on life-history (life tables, age structure, reproductive rates), ecology, environmental variation, and the effects of various types of threats are input into the software and the population size and characteristics projected into the future using stochastic simulations. Population size and extinction rates are recorded over multiple simulations. A number of software packages are used for PVA.
Conservation biologists and wildlife mangers use PVA to help determine how vulnerable their populations are to extinction. They also use PVA to help identify the most significant threats to the population and what actions might be taken to reduce the probability of extinction. The Conservation Breeding Specialist Group (CBSG) of the IUCN uses PVA to help develop recovery plans for specific species and populations using the software VORTEX.
Degrees of Endangerment on the Red List
The World Conservation Union (the premier international conservation agency, previously called the IUCN) also uses the concept of population viability, among other criteria, to help classify species according to their degree of endangerment and place them on the Red List. These are the categories of endangerment and how they are related to population viability:
Critically Endangered Species
A quantitative assessment that shows the species has a probability
of extinction in the wild is at least 50% within 10 years
or three generations, whichever is the longer (up to a maximum
of 100 years).
Endangered Species
Quantitative analysis showing the probability of extinction
in the wild is at least 20% within 20 years or five generations,
whichever is the longer (up to a maximum of 100 years).
Vulnerable Species
One where a quantitative analysis showing the probability
of extinction in the wild is at least 10% within 100 years.
The Role of National Zoological Park
National Zoo scientists have been involved in PVA workshops to help develop conservation strategies and recovery programs for many species. These include:
- Eld’s deer
- Golden lion tamarin
- Giant panda
- Florida panther
- Tamaraw (a wild water buffalo)
- Barasunga (a deer in India)
These have all be in collaboration with the Conservation Breeding Specialist Group of the IUCN.
