Delineating conservation units should be independent of effective population size

The concept of an evolutionary significant unit (ESU) is important for the delineation of intraspecific units for conservation [ 1. Funk W.C. et al. Harnessing genomics for delineating conservation units. Trends Ecol. Evol. 2012; 27: 489-496 Abstract Full Text Full Text PDF PubMed Scopus (668) Google Scholar ]. However, exact definitions have varied and a detailed framework, particularly for use with genomic data, is needed. We thus think that what Hoelzel [ 2. Hoelzel A.R. Where to now with the evolutionarily significant unit. Trends Ecol. Evol. 2023; 38: 1134-1142 Abstract Full Text Full Text PDF Scopus (0) Google Scholar ] was trying to achieve in their recent article is timely and adds to the discussion about ESU (or evolutionarily sustaining conservation units) definitions and how they should be applied. However, we argue that basing ESU decisions on effective population size (Ne), and not classifying part of a species range into an ESU unless it has a small Ne or Ne/Nc ratio (where Nc is census population size) would be detrimental to both the designation and monitoring of intra-specific units.