Effective population size

The concept of the Effective Population Size was firstly introduced by Sewall Wright in 1931 [3]. Wright introduced N (the symbol $N_e$ is mostly employed today instead) to describe the size of a diploid breeding population, which is smaller than the total number of individuals of all ages. He shows that population size fluctuations brings the effective N closer to the smaller actual population size. Also, the unequal numbers between males and females reduce the effective N. Finally, variations on the offspring numbers also reduce the effective population size. The effective population size is almost always smaller than the actual population size. A notable exception is the case of seedbanks, where the effective population size (hidden in forms of seeds) may be orders of magnitudes greater than the actual number of developed organisms [4, 5].