Problem ER5

Wright's formula describes the decrease of heterozygosity due to genetic drift from one generation to the next. For simplicity, the interval between one generation and the other was set equal to one year in the illustration presented to your class, but the formula applies more generally, provided we replace one year with one generation. Ryder et al. (Oikos, 1981) have studied three moose populations in Sweden (henceforth indicated with the letters B, C, F) which have different generation times depending on the different hunting regulations that hold for each population. More precisely:

Population B: 4.2 years from one generation to the next

Population C: 9.9 years

Population F: 7.5 years.

The graph (see Fig. 3) shows the time trend over a century of the estimated heterozygosity (natural logarithm of the proportion of heterozygous moose against time in years) for each of the three populations.

Figure 3: Variation of moose heterozygosity in three Swedish populations.

Calculate the effective population size for each of the three moose populations.