Sex Ratio Impact on Effective Population Size ($N_e$)
The effective population size ($N_e$) indicates the size of an idealized population that would experience the same genetic drift as the real population. In diploid, sexually reproducing species, $N_e$ is sensitive to the ratio of breeding males ($N_m$) to breeding females ($N_f$).
The formula relating effective population size ($N_e$) to the number of breeding males ($N_m$) and females ($N_f$) is:
$ N_e = \frac{4 N_m N_f}{N_m + N_f} $
To achieve the highest possible effective population size ($N_e$) for a constant total number of breeding individuals ($N = N_m + N_f$), the product $N_m \times N_f$ must be maximized. This occurs when $N_m$ and $N_f$ are as close as possible, meaning $N_m = N_f$.
When $N_m = N_f$, the sex ratio ($r$) is:
$ r = \frac{N_m}{N_f} = 1 $
Therefore, the effective population size is greatest when the sex ratio is 1.
Important Questions from Population characteristics
- Consider the following strains of an influenza virus and their basic reproduction numbers ($R_0$). Assuming that they are all equally virulent, which one of the following strains would be most concerning for a completely vulnerable population of humans?
- Which one of the following sets of characteristics is most likely to cause population extinction via demographic stochasticity?
- What is the relationship between effective population size ($N_e$) and total population size ($N$) of any naturally occurring eukaryotic population?
- Which of the following plots describes the expected relationship between population size (y-axis) and generation time (x-axis) in vertebrates? Here, each data point represents a different vertebrate species and the generation time is defined as the average interval between two generations.
- A population of birds has a 3:2 male to female adult sex ratio at the beginning of the breeding season. During the breeding season, every female produces 8 eggs of which 4 survive to become juveniles. A census at the end of the breeding season accurately estimates the bird population to be 1300 individuals. Assuming no deaths, the number of adult males in this population is ______ individuals.
