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

Sean Hoban, Morton Arboretum
Taylor Callicrate, Brookfield Zoo
John Clark, San Diego Zoo Global
Susan Deans, Northwestern University
Michael Dosmann, Harvard University
Jeremie Fant, Chicago Botanic Garden
Oliver Gailing, Universität Göttingen
Kayri Havens, Chicago Botanic Garden
Andrew L. Hipp, Morton Arboretum
Priyanka Dipak Kadav, Michigan Technological University
Andrea T. Kramer, Chicago Botanic Garden
Matthew Lobdell, Morton Arboretum
Tracy Magellan, Montgomery Botanical Center
Alan W. Meerow, Montgomery Botanical Center
Abby Meyer, Botanic Gardens Conservation International US
Margaret Pooler, USDA Agricultural Research Service, Washington DC
Vanessa Sanchez, Montgomery Botanical Center
Emma Spence, Morton Arboretum
Patrick Thompson, Auburn University
Raakel Toppila
Seana Walsh, National Tropical Botanical Garden
Murphy Westwood, Morton Arboretum
Wood, Chicago Botanic Garden
M. Patrick Griffith, Montgomery Botanical Center

© 2020 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License, which permits unrestricted use, provided the original author and source are credited. Publisher’s version of record:


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 analysing 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 an 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.