effective population size
Technical term in population genetics and conservation biology. Refers to the size of an idealized population that would experience the same amount of genetic drift or inbreeding as the actual population.
When the effective population size is small, genetic diversity is easily lost.
In conservation biology, estimating the effective population size is important.
個体数 simply means 'population size' (census size), while 有効個体数 is a specific genetic concept that accounts for factors like unequal sex ratios and variation in reproductive success.
Compound of 有効 (effective) + 個体数 (population size). A direct translation of the English term 'effective population size', coined in population genetics.