prov- food, water, wood, fuel,
reg- climate, flood, disease reg. pest control.
cult-aesthetic, spiritual, educational, recreational, medicinal.
The idea was that at least 50 individuals are needed to protect a species
from inbreeding effects over the short-term, and at least 500 were needed
to avoid serious effects of drift over the long term.
Hence, the 50/500 rule basically means that MVP on average should be about 2,500 - 5,000 based on genetic considerations alone. Subsequent research suggests that to avoid losing evolutionary potential within the population, this number should be even higher (up to 10,000 or more). Realistic (but generic) computer simulations suggest that at least 500
individuals are typically needed. And if populations fluctuate a lot, this number could rise to >5,000
1/5 to 1/10- of population is 'viable' so its more like 2,500-5,000 based on models.