Population Size in Evolutionary Biology Is More Than the Effective Size

Area of Science:

• Population Genetics
• Evolutionary Biology
• Conservation Genetics

Background:

• Idealized Wright-Fisher (WF) models often focus solely on effective population size (Ne) to predict evolutionary trajectories.
• The Diversity Partitioning Theorem (DPT) highlights the importance of considering both diversity and richness for system behavior.
• Current models may oversimplify population dynamics by neglecting census population size (N).

Purpose of the Study:

• To demonstrate that census population size (N) is analogous to richness and effective population size (Ne) to diversity.
• To argue for the integrated use of both N and Ne in population genetics models.
• To review evidence supporting the influence of both N and Ne on evolutionary processes and conservation.

Main Methods:

• Conceptual framework based on the Diversity Partitioning Theorem (DPT).
• Review of existing evidence on the impact of N and Ne on evolutionary trajectories.
• Application of DPT principles to population genetics.

Main Results:

• Census population size (N) represents richness, while effective population size (Ne) represents diversity.
• Both N and Ne independently and jointly influence evolutionary trajectories under neutral and adaptive processes.
• Evidence suggests N and Ne affect evolutionary potential and genetic criteria for conservation.

Conclusions:

• Accurate modeling of population evolution requires integrating both census (N) and effective (Ne) population sizes.
• Effective population size (Ne) alone is insufficient for comprehensive evolutionary and conservation assessments.
• Future applied evolutionary studies should consistently incorporate N alongside Ne for robust modeling of drift, selection, mutation, and gene flow.