Global assessment of effective population sizes: consistent taxonomic differences in meeting the 50/500 rule

Abstract

AbstractEffective population size (Ne) is a particularly useful metric for conservation as it affects genetic drift, inbreeding and adaptive potential within populations. Current guidelines recommend a minimumNeof 50 and 500 to avoid short-term inbreeding and to preserve long-term adaptive potential, respectively. However, the extent to which wild populations reach these thresholds globally has not been investigated, nor has the relationship betweenNeand human activities. Through a quantitative review, we generated a dataset with 4145 georeferencedNeestimates from 3576 unique populations, extracted from 712 articles. These data show that certain taxonomic groups are less likely to meet 50/500 thresholds and are disproportionately impacted by human activities; plant, mammal, and amphibian populations had a ≤52% probability of reachingN̂e= 50 and a <5% probability of reachingN̂e= 500. Populations listed as being of conservation concern according to the IUCN Red List had a lowerN̂ethan unlisted populations, and this relationship held true across all taxonomic groups.N̂ewas reduced in areas with a greater Global Human Footprint, especially for amphibians and mammals, however relationships varied between taxa. We also highlight several considerations for future works estimatingN̂e, including the role that gene flow and subpopulation structure plays in the estimation ofN̂ein wild populations, and the need for finer-scale taxonomic analyses. Our findings provide guidance for more specific thresholds based onNeand help prioritize assessment of populations from taxa most at risk of failing to meet conservation thresholds.