DOI: 10.5061/dryad.zgmsbcc74
title: Taxonomic similarity does not predict necessary sample size for ex situ conservation: a comparison among five genera

description: 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.
description: <b>Study Species </b> We selected
 our target perennial trees and shrubs (Table 1, Supplemental Table 1)
 because: (1) They are “exceptional species” (Pence 2013) that present
 difficulties for seedbanking (low seed production, low seed viability, or
 recalcitrant seeds), and must be conserved ex situ as living plants. (2)
 They cover a broad phylogenetic range (Monocots, Rosids, Magnoliids, and
 Cycadophytes; see Supplemental Material), so our results can be applicable
 across plant groups. (3) They represent variation in geographic ranges or
 numbers of populations. (4) All are threatened taxa, and some are
 critically endangered. We studied taxa from five
 genera. Two subspecies of <i>Hibiscus waimeae</i>, subsp.
 <i>hannerae </i>and subsp.<i> waimeae, </i>are
 endemic to the island of Kaua‘i in Hawai‘i. Both are threatened by habitat
 degradation, non-native herbivores, competition by invasive plants, seed
 predation by insects, and a possible decline or loss of native
 pollinators. <i>Hibiscus waimeae</i> subsp.
 <i>hannerae</i> is rarer- approximately 200 adult individuals
 from three valleys remain and little or no regeneration occurs. 
 <i>Magnolia ashei, </i>(Synonyms: <i>Magnolia
 macrophylla</i> ssp. <i>ashei</i> and <i>Magnolia
 macrophylla</i> var. <i>ashei</i>) is a small deciduous
 tree with large leaves and flowers that occurs in only 10 counties in
 Florida (dataset already presented in von Kohn et al. 2018).
 <i>Magnolia pyramidata </i>(Synonym: <i>Magnolia fraseri
 </i>var <i>pyramidata</i>) is<i> </i>a
 medium-sized deciduous tree reported from Texas to South Carolina, though
 with few occurrences in most states, except southern Alabama and
 northwestern Florida. <i>Pseudophoenix ekmanii</i> is
 restricted to a small area of the Dominican Republic and threatened by
 illegal destructive harvesting of sap. <i>Pseudophoenix
 sargentii</i>, the sister species of <i>P. ekmanii</i>,
 has the widest distribution of its genus, from Florida to Belize and east
 to Dominica, yet populations are isolated and locally imperiled.
 <i>Quercus georgiana </i>is a specialist on stone outcrops
 known from small, fragmented populations in Alabama, Georgia, and South
 Carolina. <i>Quercus boyntonii </i>is a small tree occurring
 on sandstone outcrops in a few counties in Alabama, making it one of the
 most range-restricted US oaks. <i>Quercus oglethorpensis</i>,
 formally described in 1940, occurs in sparse isolated populations across
 the southeast, also in granite outcrops. <i>Zamia decumbens
 </i>is a slow-growing infrequently reproducing cycad from southern
 Belize, with less than 500 extant plants, while <i>Zamia
 lucayana</i>, a fast-growing, frequently cloning cycad from the
 Bahamas, with one population of fewer than 1,000 plants on a single island
 (we expand on the dataset from Griffith et al. 2017). 
 <b>Sampling and genotyping</b> In
 situ populations were identified via Global Biodiversity Information
 Facility (GBIF) occurrence data and local collaborator networks. We
 attempted to sample as many wild populations as possible, to best
 represent the wild extant genetic diversity. Ex situ locations were
 identified via Botanic Gardens Conservation International’s PlantSearch
 (https://members.bgci.org/data_tools/plantsearch), Beckman et al. (2019),
 and personal contacts. Details of molecular markers, PCR conditions, field
 sampling, and genotyping are detailed in Supplemental Materials.
   Number of plants genotyped in this study <i>H.w. hannerae</i> 157 43 <i>H.w. waimeae</i> 73 16 <i>P. ekmanii</i> 201 93 <i>P. sargentii</i> 122 99 <i>M. ashei</i> 104 14 <i>M. pyramidata</i> 113 40 <i>Q. boyntonii</i> 244 77 <i>Q. georgiana</i> 223 36 <i>Q. oglethorpensis</i> 187 145 <i>Z. decumbens</i> 374 205 <i>Z. lucayana</i> 120 244 <b>Mean</b> 174 81 <b>Std Dev</b> 85 77
description: All data files as well as a readme are in the zip.