Diminishing return of investment in genetic diversity

Motive: Priorities in conservation management are often difficult to determine because we lack comparable biodiversity metrics. So that actions can be cost-effective, conservation decision-making and management needs such metrics. Question: What suitable metrics can compare efforts and investments in biodiversity conservation? How can established measures of genetic diversity be combined with the economic return-of-investment paradigm? Method: Use the return-of-investment approach, which has previously been restricted to issues of species diversity. Extend it to include genetic diversity. Use Taylor's power law to relate mean abundance, rates of genetic deterioration, and principles of return-of-investment. Key assumptions: We can specify the relationship between cost of conservation and population size. Time-series data are available for each population. We can approximate the effective population size (N-e) of a fluctuating population as the harmonic mean population size. Conclusion: As the financial investment in conservation increases, the estimated marginal increase in genetic diversity diminishes. One can rank actions that increase mean population size according to their associated marginal increases in genetic diversity, thus evaluating which improvements offer the most value for money.