Global contemporary effective population sizes across taxonomic groups

Effective 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 minimum Ne of
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 between Ne and human activities. Through a
quantitative review, we generated a dataset with 4610 georeferenced Ne
estimates from 3829 unique populations, extracted from 723 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 <54% probability of
reaching  = 50 and a <9% probability of reaching
 = 500. Populations listed as being of conservation concern
according to the IUCN Red List had a smaller median  than
unlisted populations, and this was consistent across all taxonomic groups.
   was reduced in areas with a greater Global Human
Footprint, especially for amphibians, birds, and mammals, however
relationships varied between taxa. We also highlight several
considerations for future works, including the role that gene flow and
subpopulation structure plays in the estimation of  in wild
populations, and the need for finer-scale taxonomic analyses. Our findings
provide guidance for more specific thresholds based on Ne and help
prioritize assessment of populations from taxa most at risk of failing to
meet conservation thresholds.