COS 190-1 - Global assessment of effective population sizes reveals deficiencies in meeting 50/500 criteria across taxa

Background/Question/Methods

Integrating genetic measures into extinction risk assessments is imperative for reducing biodiversity loss and ensuring the viability of wild populations. Effective population size (N_e) is particularly useful for conservation, as it predicts rates of genetic drift, inbreeding, and adaptive potential of a population. Current guidelines recommend minimum N_e of 50 and 500 to avoid short-term inbreeding and long-term adaptive potential, respectively. However, there is still debate over how to incorporate these guidelines into conservation management and risk assessment. To help inform the integration of N_e into management, we conducted a quantitative review of N_e estimates in wild populations. Specifically, we assessed whether taxonomic groups differ in their effective size or their likelihood of meeting the 50/500 thresholds, and whether N_e is correlated with the Global Human Footprint. To create our dataset, we screened 4513 articles from a Web of Science search to ensure they contained an N_e estimate from a wild population using a single-sample estimation technique. We extracted data from the remaining articles, filtered the dataset to remove estimates that could not be used in analyses (e.g. infinite estimates), created a map of estimates in ArcGIS, and used generalized linear mixed models to address our objectives.

Results/Conclusions

Here, we show that certain taxonomic groups have lower N_e, are less likely to meet the 50/500 thresholds, and are disproportionately impacted by human activities. Our final dataset included 4145 N_e estimates from 3576 populations, extracted from 712 articles. We found consistent taxonomic differences in N_e, with marine fishes having the largest N_e and plants, mammals, and amphibians having the smallest. Taxonomic groups also differed in their likelihood of meeting the N_e thresholds; plant, mammal, and amphibian populations had a ~50% or less chance of reaching N_e = 50 and a < 5% chance of reaching 500. Across all taxonomic groups, N_e was reduced in areas of greater human footprint, however this relationship varied in strength and direction between groups. Mammals and amphibians had the strongest negative relationship between N_e and footprint, while in plants and anadromous fishes N_e increased with increasing footprint. These results suggest that previous reviews reporting average or median N_e or N_e/N_c were not representative for certain taxonomic groups. Overall, these results may help inform changes to listing criteria, or provide a framework for prioritizing taxa that are least likely to meet thresholds or are most impacted by human activities.