Relationship of Effective to Census Size in Fluctuating Populations

Area of Science:

• Population Genetics
• Evolutionary Biology
• Ecology

Background:

• Genetic drift's rate is determined by effective population size (Ne), not census size (N).
• The ratio of effective to census size (Ne/N) is crucial for estimating Ne from census data and understanding ecological influences.
• Existing literature uses two multigenerational Ne/N ratios based on arithmetic or harmonic means.

Purpose of the Study:

• To clarify the interpretation and meaning of arithmetic and harmonic mean Ne/N ratios.
• To introduce the ratio of harmonic mean population size to arithmetic mean population size as a measure of size fluctuation impact on Ne.
• To discuss applications of these ratios in population genetics and evolutionary studies.

Main Methods:

• Analysis of existing literature on Ne/N ratios.
• Conceptual clarification of arithmetic mean Ne/N ratio (long-term Ne vs. N).
• Conceptual clarification of harmonic mean Ne/N ratio (generational Ne/N variation).

Main Results:

• The arithmetic mean Ne/N ratio relates total individuals to long-term effective population size.
• The harmonic mean Ne/N ratio quantifies generational variation in the Ne/N ratio.
• The ratio of harmonic to arithmetic mean population size effectively measures Ne reduction due to population size fluctuations.

Conclusions:

• The harmonic mean Ne/N ratio is emphasized for estimating population effective size over time using census data.
• Accurate interpretation of Ne/N ratios is vital for ecological and evolutionary research.
• Understanding these ratios aids in assessing population viability and genetic diversity.