Effective population size

Definition

Effective population size is a concept that quantifies the number of individuals in a population who contribute to the gene pool of the next generation. It differs from actual population size as it accounts for factors like unequal sex ratios, fluctuating population sizes, and variations in reproductive success. This measure is crucial for understanding genetic diversity, evolutionary potential, and the effects of linkage disequilibrium and population structure, as it influences how genes are passed through generations.

5 Must Know Facts For Your Next Test

1. Effective population size is often smaller than the actual census size due to factors such as sex ratio imbalances or unequal reproductive success among individuals.
2. Linkage disequilibrium can be affected by effective population size; smaller effective populations can lead to higher linkage disequilibrium due to reduced recombination.
3. In populations with structure or admixture, effective population size helps to gauge how genetic diversity is maintained or lost across subpopulations.
4. Effective population size can be estimated using formulas that incorporate census size and the variance in reproductive success among individuals.
5. Changes in effective population size can influence the rate of adaptation and the risk of extinction for species facing environmental changes.

Review Questions

• How does effective population size impact genetic diversity and linkage disequilibrium within a population?
  • Effective population size directly influences genetic diversity because a smaller effective size limits the number of breeding individuals contributing genes to future generations. This can lead to increased linkage disequilibrium, as alleles at different loci may become associated due to reduced recombination events. Essentially, if fewer individuals reproduce effectively, there's less opportunity for new combinations of alleles, which diminishes genetic variability over time.
• Discuss how effective population size is related to population structure and admixture and its implications for evolutionary dynamics.
  • Effective population size plays a crucial role in understanding how genetic variation is maintained or lost in structured or admixed populations. In populations that are subdivided into smaller groups, the effective size can be lower than the actual size due to limited gene flow between groups. This can affect evolutionary dynamics by altering rates of adaptation and genetic drift within subpopulations, potentially leading to divergence or increased risk of extinction if connectivity is poor.
• Evaluate the significance of effective population size in conservation genetics and its implications for species survival under changing environments.
  • Effective population size is essential in conservation genetics as it provides insight into a species' ability to adapt and survive in changing environments. A low effective population size increases the risk of inbreeding depression and reduces genetic diversity, which can impair adaptive potential. Understanding this concept helps conservationists develop strategies that enhance gene flow and maintain larger effective sizes to promote resilience against environmental stresses and ensure long-term species viability.

Related terms

Linkage disequilibrium: A non-random association of alleles at different loci that can indicate how genes are inherited together within a population.

Genetic drift: The random fluctuations in allele frequencies within a population, especially in small populations, that can lead to changes in genetic diversity over time.

Population bottleneck: An event that drastically reduces the size of a population, which can lead to a significant loss of genetic diversity and affect effective population size.