Nature, in Code

Effective Population Size: Sex Ratio

The effective population size, N_e, is the size of a population that behaves like an ideal (Wright-Fisher) population of size N_e. The sex ratio of a population affects its effective population size. In a population with N_m males and N_f females, the effective population size is:

$$N_e = {4 N_{m} N_{f} \over N}$$
The plot below shows how an unequal sex ratio, expressed as the fraction of males in the population, reduces the effective population size N_e (relative to the census population size N).

Code

var data=[];
var x_max = 1;

for (var i = 0; i <= x_max + 0.005; i = i + 0.01) {
	var male_to_female_ratio = i;
	Ne_to_N_ratio = 4 * male_to_female_ratio * (1 - male_to_female_ratio);
	data.push(Ne_to_N_ratio);
}

draw_line_chart(data,"Proportion Males","Ne / N",[],x_max);
			

Note: the draw_line_chart function is built with D3.js and can be found here.