Enter your Number of Males (Nm) and Number of Females (Nf) into the Effective Population Size Calculator to find the Effective Population Size (Ne), Census Population Size, Sex Ratio, and Ne/Census Ratio — revealing how genetic diversity compares to a simple headcount.
Effective Population Size (Ne)
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Census Population Size
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Sex Ratio (M:F)
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Ne/Census Ratio
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Effective population size (Ne) is the number of individuals in an idealized population that would experience the same genetic drift as the actual population. It's crucial for understanding genetic diversity, inbreeding risk, and long-term population viability.
Effective population size is calculated using the formula: Ne = (4 × Nm × Nf) / (Nm + Nf), where Nm is the number of breeding males and Nf is the number of breeding females. This accounts for unequal sex ratios that reduce genetic diversity.
Effective population size is typically smaller because not all individuals reproduce, sex ratios may be unequal, and reproductive success varies among individuals. These factors reduce the genetic contribution to the next generation.
Unequal sex ratios significantly reduce effective population size. For example, a population with 90 males and 10 females has a much smaller Ne than one with 50 males and 50 females, even though both have 100 total individuals.
Generally, an effective population size of at least 50 is needed to avoid immediate inbreeding depression, while 500+ is recommended for long-term evolutionary potential. However, these thresholds vary by species and circumstances.
Smaller effective population sizes lead to greater genetic drift, faster loss of genetic variation, and increased inbreeding. This can reduce fitness and adaptive potential, making populations more vulnerable to environmental changes.