MINIMUM VIABLE POPULATION (MVP)

The minimum number of interacting individuals of a species that can provide a specified (often 90, 95 or 99%), probability of persistence of a population for a specified number (often 50, 100 or 1000) of years. Factors that can affect the survival of a population include demographic, environmental, and genetic stochasticity.

MVP is important when decisions are made which can alter the available habitat, and consequently the species population and risk of catastrophic extinction.

A statistical model of Population Viability Analysis (PVA) is used in practice to estimate MVP and then to make management decisions.

PVA analysis evaluates interacting characteristics that affect a population's survival. Eg: low longevity and fecundity, and a high demographic stochasticity and background environmental variation would mean a very high MVP estimate. PVA can also give estimates of the effect of balancing environmental characteristics, such as habitat quality (higher population density), and area (increased area is safer in the event of extreme events).

PVA Deterministic characteristics (usually demographic and biological ) such as:

  • Longevity
  • Fecundity
  • Mortality
  • Per. capita growth rate
  • A species type of survivorship curve

And relates these to:

PVA Probabilistic characteristics such as:

  • Demographic stochasticity (chance variation in births and deaths)
  • Background environmental variation (eg; year to year difference in rainfall)
  • Castrophes (episodic extreme events such as fires or droughts)
  • Inbreeding (more than 50 individuals rule; alters expression of deleterious genes)
  • Genetic drift (more than 500 individuals rule; random loss of genetic diversity in small populations)

NB: Scientific theory must be proved through empirical evidence. Below is my summary of an interesting empirical estimation of the MVP proved over 1000 years isolation of populations using the presence or absence of primates in the islands of South East Asia.

The original study is referenced as: A.H. Harcourt. 2002. Empirical estimates of minimum viable population sizes for primates: tens to tens of thousands? Animal Conservation, 5:237-244. Abstract.

'The population of primates lowers with smaller island size. The MVP is proposed to be the number of a species on the smallest islands on which the species still survive. Results for eight to 10 genera of primates on 35 islands indicate MVPs of perhaps a few score for loris and macaques to several thousands, or scores of thousands, for orang-utans and siamangs. Large-bodied primates (lower fecundity?) have significantly larger MVPs than do small-bodied primates.'

For further publications by Professor A.H. Harcourt see http://www.anthro.ucdavis.edu/faculty/harcourt/publ.htm.