Question

What is the probability of extinction for a species of rare bird with an initial population size of 118, b = 1.39, d = 1.31. What if there were only 20 birds to start?

Answer 1

Initial population size N₀ = 118 or N₀ = 20.

Birth rate b = 1.39, death rate d = 1.31 and b > d.

The probability of extinction E can be calculated from

   $PE = \left( \frac{d}{b}\right )^{N_0}$

When N₀ = 118, PE = (1.31/1.39)¹¹⁸ = 9.17 x 10^-4.

When N₀ = 20, PE = (1.31/1.39)²⁰ = 0.306.