N_e Does Not Provide Sufficient Information on Allelic Variation: Suggestions to Fill the Gap

Conservation success depends on translating theory into practical guidance and tools that are relevant and useful for non-scientists. While the complexity of population genetics has challenged the usage of straightforward metrics for conservation, several practical guidelines have been advanced, such as those regarding effective population size (N _e ). Allendorf et al. highlight limitations of N _e as a metric for practical use. Specifically, they demonstrate that while N _e is sufficient for predicting heterozygosity, it is not predictive of the number of alleles, another key variable in conservation genetics. This has important implications for N _e -based metrics, such as the N _e 500 indicator recently adopted in the Convention on Biological Diversity's Kunming-Montreal Global Biodiversity Framework. As developers and advocates of the N _e 500 indicator, we agree with this assessment, and acknowledge that N _e does not comprehensively predict changes in allelic variation. In this article we briefly summarize several major points in Allendorf et al. and provide practical suggestions to better account for allelic variation during indicator assessments. These suggestions include reporting major declines in N _c as part of genetic assessments, clearly articulating the intention and caveats of the N _e 500 indicator, integrating simulations into genetic assessments, and assessing the number of genetically distinct populations. We conclude that the N _e 500 indicator remains a valuable metric uniquely capable of capturing critical aspects of a species' genetic status while remaining accessible and interpretable to policymakers and other non-geneticists. By acknowledging the limitations of focusing solely on N _e and providing options for more thorough and nuanced understandings of genetic diversity, we hope to guide future usage of the N _e 500 indicator and help bridge the gap between conservation genetics theory and practice.