Genetic Bottleneck in Wildlife Populations

A genetic bottleneck occurs when a population is sharply reduced, leaving only a small and unrepresentative sample of its original gene pool. The resulting low effective population size, meaning the number of individuals actually contributing genes to future generations, makes random genetic change and mating among relatives more influential. Its effects may persist even after population numbers recover.

How genetic diversity is lost

• In a small breeding population, genetic drift can randomly eliminate alleles and alter allele frequencies, irrespective of whether those alleles are advantageous.
• Rare alleles are especially likely to disappear, reducing allelic richness and genetic variation.
• Mating among relatives increases homozygosity and can expose harmful recessive alleles, causing inbreeding depression through reduced survival, fertility or reproductive success.
• Numerical recovery alone does not restore lost alleles quickly; recovery generally requires mutation or gene flow from another population.

Consequences for long-term viability

Reduced variation can weaken the population's adaptive potential, limiting its capacity to respond to diseases, climatic shifts and other environmental changes.

• Lower survival and reproduction caused by inbreeding can accelerate further population decline.
• Small populations are also more vulnerable to demographic fluctuations and chance environmental events.
• Genetic deterioration and declining numbers can reinforce each other in an extinction vortex, progressively raising extinction risk.

Conservation implications

Conservation must increase both population numbers and genetic health rather than treating headcount alone as recovery.

• Protecting and reconnecting habitats promotes dispersal and gene flow between isolated populations.
• Carefully planned translocation may provide genetic rescue by introducing variation and reducing inbreeding, but source compatibility and ecological risks must be assessed.
• Genetic monitoring, balanced breeding contributions and removal of the original causes of decline help rebuild effective population size.