Taxonomic similarity does not predict necessary sample size for ex situ conservation: a comparison among five genera

Effectively conserving biodiversity with limited resources requires
scientifically informed and efficient strategies. Guidance is particularly
needed on how many living plants are necessary to conserve a threshold
level of genetic diversity in ex situ collections. We investigated this
question for 11 taxa across five genera. In this first study analyzing and
optimizing ex situ genetic diversity across multiple genera, we found that
the percentage of extant genetic diversity currently conserved varies
among taxa, from 40 to 95%. Most taxa are well below genetic conservation
targets. Resampling datasets showed that ideal collection sizes vary
widely even within a genus: one taxon typically required at least 50% more
individuals than another (though Quercus was an exception). Still, across
taxa, the minimum collection size to achieve genetic conservation goals is
within one order of magnitude. Current collections are also suboptimal:
they could remain the same size yet capture twice the genetic diversity
with improved sampling design. We term this deficiency the “genetic
conservation gap.” Lastly, we show that minimum collection sizes are
influenced by collection priorities regarding the genetic diversity
target. In summary, current collections are insufficient (not reaching
targets) and suboptimal (not efficiently designed), and we show how
improvements can be made.