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Population viability analysis

Population viability analysis. PVA. What is PVA?. The use of quantitative methods to predict the likely future status of a population or collection of populations Crouse et al 1987 is an example of a PVA. Uses of PVA. Assessing the extinction risk of a single population

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Population viability analysis

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  1. Population viability analysis PVA

  2. What is PVA? • The use of quantitative methods to predict the likely future status of a population or collection of populations • Crouse et al 1987 is an example of a PVA

  3. Uses of PVA • Assessing the extinction risk of a single population • Grizzly bears in Yellowstone National Park • PVA concluded that bears have moderate chance of survival for 100 years, low for 300 • Along with law suits resulted in reduced clear cutting and mining development • Prevented premature removal of grizzly from ESA “threatened” list • Northern spotted owl • Showed population was declining in face of logging pressure • Resulted in listing as threatened and reduced logging

  4. Uses of PVA • Comparing relative risks of multiple populations • Identifying scope of the problem • Further PVA’s showed 10 of 11 owl populations declining • Designating priority populations • Designating minimal set of populations to be preserved • Useful for groups such as the Nature Conservancy

  5. Uses of PVA • Analyzing and synthesizing monitoring data • Are management strategies working? • Is the species still imperiled? • Northern gray whale populations increased from 1965 to mid 1990’s. De-listed in 1994. PVA showed that this was warranted

  6. Uses of PVA • Identifying key life stages or demographic parameters • Loggerhead turtle example

  7. Uses of PVA • Determining how large a reserve needs to be to achieve the desired level of protection • PVA showed that at least 2,500 square kilometers are needed for management of African elephant populations facing drought

  8. Uses of PVA • Determining how many individuals to release to establish a new population • Suppose you have 10 possible sites and 100 captively bred wolves. How many go to each site? • What information would you need to decide? • About the organism? • About the habitat?

  9. Uses of PVA • Setting limits on harvest from a population • Dr. Lubbers’ data on ginseng populations – how much harvesting can a population absorb • Inadvertent taking • By catch (loggerhead sea turtles) • Collisions (Florida manatee, Florida Panther) • Destruction of habitat (Northern spotted owl)

  10. Uses of PVA • Determining how many populations are needed to preserve a species • Applied to multiple isolated subpopulations and metapopulations (what is the difference?) • Furbish’s lousewort • restricted to 15 populations along a river in Maine • All local populations are at a high risk of extinction due to disturbance regime • Protecting extant populations cannot ensure species survival • Protection requires establishment of new populations

  11. Types of PVA • PVA includes a range of modeling methods and data analysis • Count-based PVAs • Based on numbers of individuals in the population or subpopulation (census data) • All individuals treated as identical

  12. Types of PVA • Demographic PVAs • Based on rates of demographic processes (e.g. birth, death, growth) • Useful for “structured populations” • Expensive and labor-intensive • Why would demographic PVAs be superior in some cases?

  13. Types of PVA • Multi-site PVAs • Used for modeling metapopulations • When is this necessary? • What are the drawbacks of this approach? • Which elements should be “simplified” in a population model? • From incidence function models to SEIB (spatially-explicit, individual-based) models

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