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A peer-reviewed version of this preprint was published in PeerJ on 21 February 2017.

View the peer-reviewed version (peerj.com/articles/2984), which is the preferred citable publication unless you specifically need to cite this preprint.

Treurnicht M, Colville JF, Joppa LN, Huyser O, Manning J. 2017. Counting complete? Finalising the inventory of a global hotspot. PeerJ 5:e2984 https://doi.org/10.7717/peerj.2984 Counting Complete? Finalising the plant inventory of a global biodiversity hotspot

Martina Treurnicht Corresp., 1, 2, 3 , Jonathan F Colville 4, 5 , Lucas N Joppa 6 , Onno Huyser 7 , John Manning 8, 9

1 Conservation Ecology and Entomology, University of Stellenbosch, Stellenbosch, , South 2 Institute of Landscape and Plant Ecology, University of Hohenheim, Stuttgart, Germany 3 South African Environmental Observation Network Node, , Western Cape, 4 Kirstenbosch Research Centre, South African National Biodiversity Institute, Cape Town, Western Cape, South Africa 5 Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, Cape Town, Western Cape, South Africa 6 Computational Ecology, Microsoft Research, Cambridge, United Kingdom 7 Centre for Biodiversity Conservation, Kirstenbosch Botanical Gardens, Table Mountain Fund (WWF-SA), Cape Town, Western Cape, South Africa 8 Compton Herbarium, South African National Biodiversity Institute, Cape Town, Western Cape, South Africa 9 Research Centre for Plant Growth and Development, University of KwaZulu-Natal, Pietermaritzburg, KwaZulu-Natal, South Africa

Corresponding Author: Martina Treurnicht Email address: [email protected]

The – the world’s smallest, but third richest hotspot – experienced sustained levels of taxonomic effort and exploration for almost three centuries resulting in a near-complete plant inventory. Here we analyse, for a core component of this flora, trends over a 250 year period in taxonomic effort and species discovery linked to ecological and conservation attributes. We show that >40% of species were described within the initial 100 years, followed by a steady rate of description, culminating in <1% of the flora estimated still to be described. A relatively constant cohort of taxonomists working at their ‘taxonomic maximum’ was seen across 250 years, while rates of description remained independent of plant growth-form. Since 1950, narrow-range taxa constituted significantly greater proportions of species discoveries, highlighting the fraction of undiscovered species which exist as localised endemics and thus of high conservation value. In the context of initiated global strategic plans for biodiversity, our dataset provides real world insights for other hotspots to consider the effort required for attaining set targets of comprehensive plant inventories.

PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2573v1 | CC BY 4.0 Open Access | rec: 3 Nov 2016, publ: 1 Counting Complete? Finalising the plant inventory of a global

2 biodiversity hotspot

3

4 Martina Treurnicht 1,2,3*, Jonathan F. Colville 4,5, Lucas N. Joppa 6, Onno Huyser 7 & John 5 Manning 8,9

6

7 1 Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, 8 South Africa

9 2 South African Environmental Observation Network Fynbos Node, Centre for Biodiversity 10 Conservation, Kirstenbosch Botanical Gardens, Cape Town, South Africa

11 3 Institute of Landscape and Plant Ecology, University of Hohenheim, Stuttgart, Germany

12 4 South African National Biodiversity Institute, Kirstenbosch Research Centre, Cape Town, 13 South Africa

14 5 Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, 15 University of Cape Town, Cape Town, South Africa

16 6 Microsoft Research, Computational Ecology, Cambridge, United Kingdom

17 7 Table Mountain Fund (WWF-SA), Centre for Biodiversity Conservation, Kirstenbosch 18 Botanical Gardens, Cape Town, South Africa

19 8 Research Centre for Plant Growth and Development, School of Life Sciences, University of 20 KwaZulu-Natal, Pietermaritzburg, South Africa

21 9 Compton Herbarium, South African National Biodiversity Institute, Cape Town, South Africa

22

23 *Corresponding author

24 Martina Treurnicht; [email protected]

25

1

26 Abstract

27 The Cape Floristic Region – the world’s smallest, but third richest hotspot – experienced

28 sustained levels of taxonomic effort and exploration for almost three centuries resulting in a

29 near-complete plant species inventory. Here we analyse, for a core component of this flora,

30 trends over a 250 year period in taxonomic effort and species discovery linked to ecological

31 and conservation attributes. We show that >40% of species were described within the initial

32 100 years, followed by a steady rate of description, culminating in <1% of the flora estimated

33 still to be described. A relatively constant cohort of taxonomists working at their ‘taxonomic

34 maximum’ was seen across 250 years, while rates of description remained independent of plant

35 growth-form. Since 1950, narrow-range taxa constituted significantly greater proportions of

36 species discoveries, highlighting the fraction of undiscovered species which exist as localised

37 endemics and thus of high conservation value. In the context of initiated global strategic plans

38 for biodiversity, our dataset provides important real-world insights for other hotspots to

39 consider the effort required for attaining set targets of comprehensive plant inventories.

2

40 Introduction

41 Global biodiversity hotspots are species-rich areas of high conservation priority, with

42 significant numbers of rare and undiscovered species facing increasing threats of extinction

43 (Myers et al., 2000; Giam & Scheffers, 2012; Scheffers et al., 2012). They provide insight into

44 ecological and evolutionary patterns associated with mega-diverse regions (Allsopp, Colville

45 & Verboom, 2014) and the taxonomic and conservation efforts necessary to document and

46 manage this biodiversity (Cowling et al., 2003). Key to this is the urgent (Scheffers et al., 2012)

47 but challenging (May, 2011) necessity for an adequate bio-inventory (Pimm et al., 2014).

48

49 Projections suggest that we are decades or more away from achieving acceptable bio-

50 inventories for most hotspots and taxonomic groups (Mora et al., 2011). Compounding the

51 uncertainty of how, when, or even if we will achieve this is the lack of adequate data on which

52 to base realistic predictions. Most hotspots are historically under-resourced in terms of

53 taxonomic and scientific effort (Cowling et al., 2010; Grieneisen et al., 2014), and are far short

54 of achieving near-complete inventories for even conspicuous taxa such as flowering

55 (Sobral & Stehmann, 2009; Forzza & Baumgratz, 2012). Real data on the rates of species

56 descriptions from a particular area is a first requirement for assessing the time-span needed for

57 a near-complete bio-inventory.

58

59 Recent analyses suggest that the majority of plant species still to be described are to be found

60 within biodiversity hotspots (Sobral & Stehmann, 2009; Joppa et al., 2011a). Although the rate

61 at which species are documented is determined by taxonomic endeavour, the number of active

62 taxonomists and their individual productivity varies greatly across different taxonomic groups

63 (Joppa et al., 2011a; Bacher, 2012; Joppa, Roberts & Pimm, 2012). No comparable analyses

64 exist for an entire flora. Analysing trends in species documentation over time for an entire 3

65 floristic hotspot will permit real-world predictions of taxonomic effort necessary to describe

66 the full species complement of the hotspot. These can serve as guidelines for other species-rich

67 areas in estimating the time frames required for meeting inventory targets such as the

68 Convention on Biological Diversity targets for 2020 (http://www.cbd.int/gspc/targets.shtml).

69 These estimates can guide the assessment of possible alternative conservation strategies that

70 are less reliant on near-complete species inventories (Grantham et al., 2009; Cowling et al.,

71 2010; Forest et al., 2015).

72

73 We focus here on the Cape Floristic Region (CFR, South Africa), one of the smallest (~91 000

74 km2) of the 25 biodiversity hotspots first identified by Myers et al. (2000), with a flora that is

75 arguably one of the best known among the botanical hotspots. The CFR has been the subject of

76 almost three centuries of intense botanical focus, with a current total of ca. 9 400 recognised

77 species of vascular plants and >68% regional (Manning & Goldblatt, 2012). Due to

78 its small size and long legacy of exploration and taxonomic effort, the inventory of vascular

79 plants for the CFR appears to be nearly complete, although new species are still being

80 discovered and described annually (Manning & Goldblatt, 2012; SANBI, 2015). In this study,

81 we analyse rates of plant species discovery and associated taxonomic effort in the CFR over a

82 250 year period (1753-2012), utilising techniques similar to those employed by Joppa, Roberts

83 & Pimm (2011b; 2011c). We apply these on a subset of >2400 ‘Cape clade species’ (sensu

84 Linder, 2003), representing groups that are centred in the CFR and thus contain a

85 disproportionally high number of highly endemic and threatened taxa (Raimondo et al., 2009).

86 This allowed us to search for trends in species discovery and taxonomic activity in the study

87 region, additionally we explored trends linked to abundance, ecology and conservation status.

88 Finally, we also considered whether it is possible to estimate how many ‘missing species’

89 (Solow & Smith, 2005) remain in the CFR and by what date we can expect to find them.

4

90 Materials and methods

91 We analysed data for 2434 species selected from the 33 ‘Cape clades’ identified by Linder

92 (2003) as “…those clades that have had most of their evolutionary history in the Cape Floristic

93 Region” (Table S1). These clades represent lineages for which we expect the highest rates of

94 description of new species in recent decades (Webb, Slik, & Triono, 2010). We restricted our

95 selection within the clades (i) to genera that have been comprehensively and relatively recently

96 monographed and (ii) included representatives from a wide spectrum of families and growth

97 forms. Only currently accepted species as listed in Manning & Goldblatt (2012) were accepted.

98 Our selection comprises 55% of Cape clade species and 26% of all species in the

99 CFR.

100

101 We determined the date of publication of the protologue for each species, commencing with the

102 publication of Species Plantarum (Linnaeus, 1753) and terminating with the publication of

103 Cape Plants (Manning & Goldblatt, 2012). Data on species habit and growth form were culled

104 from Manning & Goldblatt (2012) and from PRECIS (National Herbarium Pretoria

105 Computerised Information System; Germishuizen et al., 2006). Species were classified as

106 annuals, geophytes, graminoids, herbaceous perennials or . None of the species in the

107 study group were trees. Species distributions were summarised following the phytogeographic

108 centres (sensu Brown & Stuart, 2009) as given in Manning & Goldblatt (2012). Species were

109 considered to be ‘local’ if present in a single phytogeographic centre and ‘widespread’ (or non-

110 local) if present in more than one phytogeographic centre.

111

112 We used sample scripts and functions, readily available online (from Joppa, Roberts & Pimm,

113 2011b), to analyse trends in species discovery and taxonomic activity over ca. 250 years (1753–

114 2012). More specifically, we show “moving average functions” (sensu Joppa, Roberts & Pimm,

5

115 2011b) described over five year intervals for (a) the total number of species described, (b) the

116 cumulative number of species, (c) the number of taxonomists involved in describing species

117 and (d) species described by taxonomists. We then additionally show the (e) relative

118 contribution of each increment to the flora by dividing each accumulated five year subtotal by

119 the total number of species (2434) described over the entire study period (i.e. proportion new

120 species (%) described). Finally, we explore the cumulative number of species by ecological

121 attributes, i.e. (f) growth form and (g) phytogeographic centre (a proxy for abundance; from

122 Manning & Goldblatt, 2012). All analyses were performed in R version 3.3.1 (R Development

123 Core Team, 2016).

124

125 Results

126 The number of vascular plant species described from the CFR for the 250 year period from

127 1753–2012 has fluctuated widely over any given five year increment. From a number of 106

128 species described in 1830–1835 to 9 species described during 1870–1875 (Fig 1a; Table S2).

129 Then the post-World War 2 period (1945–1990) is characterised by relatively steady rate in

130 species description of between 48 and 76 species per five year increment (Fig 1a; Table S2).

131 Peaks in the latter period represent the dates of publication of significant generic revisions or

132 monographs (e.g. Goldblatt, 1978; Bond & Goldblatt, 1984; Linder, 2003). Overall, however,

133 species in the sample group were described at a remarkably consistent rate over the entire study

134 period (Fig 1b), with at most only a very slight positive trend in number of species described

135 (x= 46.51 ± 20.03) per increment.

136

137 The number of publishing taxonomists per increment ranged from 3 to 18 with a very slight

138 trend towards more taxonomists over time (Fig 1c), balanced by a corresponding decline in the

139 number of species published per taxonomist (Fig 1d).

6

140 Naturally (from Fig. 1a-b), the number of new species described each half decade represents a

141 diminishing proportion of the total number of species (Fig 1e) but the relationship is strongly

142 logarithmic, with a large proportion (41%) of species described within the first century of

143 taxonomic study (1753–1850). Hereafter the additional species contributions stabilised at a

144 modest incremental increase of 3% for the period 1850–1985, with a further decline to the

145 current level of 1.36% (1990–2012).

146

147 Rates of description of species remained relatively consistent from 1753–2012 regardless of

148 growth form (Fig 1f), with shrubby species described at a higher rate than other growth forms.

149 Significantly, however, analysis of the cumulative species by species distribution reveals a

150 critical difference between local and widespread (or non-local) species (Fig 1g). Local and non-

151 local species accumulated at comparable rates over the period 1753–1930, with a consistently

152 greater number of widespread species being named. The period after 1950, however, documents

153 a deceleration in the description of non-local taxa and a marked acceleration in the description

154 of local taxa. From 1950 onwards, the number of local taxa described per half decade exceeds

155 the number of widespread taxa described in the same period, with a widening difference

156 between the two (Fig. 1g).

157

158 Discussion

159 Our study shows that there has been a sustained level of taxonomic interest in the CFR over

160 more than 250 years of active botanical study. Species have been described at a constant rate

161 over this entire period, reflecting a sustained level of taxonomic output by a relatively stable

162 number of active taxonomists. From this, we conclude that there is a finite number of species

163 that can be processed by any taxonomist over a fixed period in their working life. Specifically,

7

164 there seems to be a maximum limit to the ‘productivity’ of any taxonomist, a measure that we

165 term here the ‘taxonomic maximum’. On the assumption that botanical study in the CFR has

166 proceeded at or near the taxonomic maximum, we conclude that it is unreasonable to expect an

167 increase in individual taxonomic output.

168

169 The CFR has been the subject of botanical exploration since the fifteenth century, with a period

170 of particular intensive discovery and documentation in the late eighteenth century (Glen &

171 Germishuizen, 2010). This early knowledge was consolidated and expanded in the nineteenth

172 century in the publication of the Flora capensis (Harvey, 1869-1900). Taxonomic activity over

173 this period, based on typological principles and practised largely by non-resident scientists from

174 foreign institutes in Britain and , resulted primarily in a proliferation of names. The early

175 part of the twentieth century was a period of more intensive study associated with the

176 establishment of the region’s two primary taxonomic institutes, the University of Cape Town

177 and Kirstenbosch Botanical Garden, with a resident staff. Botanists at these institutes studied

178 the local flora in the herbarium and in the field, and also encouraged collecting among local

179 amateurs. Current civil society programmes continue this valuable contribution (SANBI, 2015).

180 The actual taxonomic effort expended in the early twentieth century is obscured in our analyses

181 by the fact that we cannot reflect the number of names that disappeared into synonymy during

182 each half decade.

183

184 Professional taxonomists remain the critical resource and our findings suggest that the most

185 effective way of increasing ‘taxonomic effort’, and thus the rate at which any flora is

186 catalogued, is by increasing the number of active taxonomists (e.g. Godfray, 2002; Bacher,

187 2012). Our analysis of the activity of taxonomists also reflects the trend towards multi-authored

188 species, as discerned by Joppa, Roberts & Pimm (2011b).

189 8

190 The proportionally higher number of shrubby species in our study group reflects the

191 predominance of this habit (54% of the flora) in the CFR study region (Goldblatt & Manning,

192 2002; Linder, 2003). Other categories are also broadly consistent with their representation in

193 the flora as a whole but reflect sampling bias in the study group (notably graminoids) which are

194 overrepresented in the sample.

195

196 The documentation of the CFR flora has proceeded as a logarithmic function, with a long tail

197 representing an incremental addition to the floristic inventory of 1–5% of the flora every five

198 years. The ‘missing species’ thus comprise an insignificant proportion of those already

199 described. Based on the fact that some half of the CFR species are members of the Cape clades

200 used to generate these trends, we estimate that a maximum of 50–100 ‘missing species’ remain

201 in the CFR. This is a minute proportion of the flora (<1%) that falls far below the predicted

202 numbers of missing plant species (ca. 15%) for other hotspots (Joppa, Roberts & Pimm, 2011c;

203 see also Webb, Slik, & Triono, 2010; Laurance & Edwards, 2011; Scheffers et al., 2012). For

204 most practical purposes, therefore, the botanical diversity in the CFR can be considered to be

205 adequately known. Critically, however, the ‘missing species’ are likely to be local endemics

206 and vulnerable to extinction (e.g. Fig. 1g).

207

208 The Cape flora is characterised by high numbers of local endemics, reflected in the high levels

209 of beta and gamma diversity across the region (Cowling, Holmes & Rebelo, 1992; Goldblatt &

210 Manning, 2000). The distinction between local and more widespread species appears to be the

211 primary determinant of the likelihood of discovering new species in the CFR since 1950. This

212 conclusion is universal to global biodiversity hotspots (Scheffers et al., 2012).

213

214 The number of local endemics in the CFR described in the past 50 years is high enough to offset

215 the declining rate at which more widespread taxa are being discovered. This finding has 9

216 significant implications for conservation in the CFR, and possibly other global hotspots, in

217 confirming that locally endemic taxa are among the last to be discovered. This increases the

218 risk that they will be driven to extinction before being documented. To circumvent this it is

219 necessary to maintain the level of taxonomic effort and to increase the level of exploration of

220 the flora.

221

222 The species accumulation trends that we have documented here demonstrate that the CFR is in

223 an enviable position among global biodiversity hotspots in that its botanical diversity is now

224 essentially completely documented. Firstly, we are only able to reach this conclusion because

225 the region has been extensively and intensively studied over a period of almost three centuries

226 with a relatively constant taxonomic effort. The situation in other hotspots and among other

227 taxonomic groups (e.g. Picker, Colville & Van Noort, 2002) is unlikely to be so favourable.

228 Secondly, only once near complete species inventories exist, the output of timely exploration,

229 can we develop conservation assessments of individual species (e.g. Raimondo et al., 2009).

230 The first objective of the GSPC is to ensure that “plant diversity is well understood, documented

231 and recognised” (GSPC, https://www.cbd.int/gspc/objectives.shtml) and our CFR case study

232 directly illustrates that obtaining such a basis for biodiversity estimates takes both time and

233 taxonomic investment.

234

235 Finally, even if most plant species in the CFR have been named, there remains several

236 undiscovered species and we further lack information on (e.g.) abundance, distribution and the

237 ecology of species (e.g. Raimondo et al., 2009; Costello, Vanhoorne, & Appeltans, 2015).

238 However, more recently national threatened species programmes, local citizen science projects

239 and taxonomic revisions contributed significantly to both species discoveries and unknown

240 locality records of species in the CFR (e.g. Raimondo et al., 2009; Manning & Goldblatt, 2012;

241 SANBI, 2015). Maintaining or even increasing the funding that supports such collaborative 10

242 efforts is thus urgent, especially in regions which may not have a long legacy of botanical

243 exploration. Key to filling these gaps is thus to increase collaboration amongst international

244 taxonomists, maintain current taxonomic effort and increase expertise by including non-

245 specialists (Costello, Vanhoorne, & Appeltans, 2015). The CFR case study we have presented

246 here provides a valuable but rare real world dataset that other hotspots can use to estimate the

247 resources in time, effort, taxonomic output and potential alternative strategies that would be

248 needed to achieve adequate documentation of plant species.

249

250

251 Acknowledgements

252 We are grateful to Domitilla Raimondo, Lize Von Staden (Threatened Species Programme,

253 South African National Biodiversity Institute (SANBI)) and Ismail Ebrahim (SANBI) for

254 insightful discussions; Ilva Rogers and Les Powrie (SANBI) for assistance with data.

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349 Figures

350 Figure 1. Trends over time (1753 – 2012) in species discovery rates and taxonomic effort in

351 the Cape Floristic Region, South Africa: (a) Total number of species described, (b) the

352 cumulative number of species, (c) the number of taxonomists involved in describing species

353 and (d) the species described per taxonomist. Plotted lines are moving average functions (sensu

354 Joppa, Roberts & Pimm, 2011b) across five year time intervals. (e) The proportion (%) of new

355 species described, (f) the cumulative number of species per growth form and (g)

356 phytogeographic centre (0 = widespread and 1 = local; see main text for details). Trend lines

357 (dashed black) in (a-c) are based on linear model fits whereas the trend line in (e) is based on a

358 mean rate of 8.98 species described per 5 interval across the study period (i.e. 1753 – 2012).

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359 360 Figure 1.

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Supplemental Information

Supplemental information for this article can be found online.

Table S1. Taxa used to analyse trends over time in taxonomic effort and species discovery rates in the Cape Floristic Region (South Africa) selected from among the 33 ‘Cape clades’ identified by Linder (2003).

Table S2. Values of plotted data based on moving average functions (sensu Joppa, Roberts & Pimm, 2011b), presented in Fig 1 (a-d) which shows trends over time (start year = 1753), in species discovery and taxonomic effort in the Cape Floristic Region (South Africa). See main text for full description of methods.

18

Table S1.

Family Genera included Number of species included Anthanasia, Bryomorphe, , Disparago, Elytropappus, , Gymnostephium, Hymenolepis, 269 Mairia, Metalasia, , Stoebe, Ursinia, Zyrphelis Audouinia, Berzelia, Brunia, Linconia, Staavia, Thamnea 78 BORAGINACEAE Lobostemon 29 CYPERACEAE Ficinia, Tetraria 96 Aspalathus, Amphithalea, Liparia, Podylyria, Rafnia, Xiphotheca 378 GEISSOLOMATACEAE Geissoloma 1 GRUBBIACEAE Grubbia 3 Bobartia, Freesia, Geissorhiza, Hesperantha, Ixia, Klattia, Nivenia, Sparaxis, Thereianthus, , 284 Tritoniopsis, Witsenia Ceratandra, Evotella, Pterygodium 32 Brachysiphon, Endonema, Glischrocolla, Penaea, Saltera, Sonderothamnus, Stylapterus 23 Ehrharta, Pentameris 82 POLYGALACEAE Muraltia 109 , , , , , , , , , 329 , , Anthochortus, Askidiosperma, , Ceratocaryum, Elegia, Hydrophilus, , Mastersiella, 342 Nevillea, Platycaulos, , , Soroveta, , , ROSACEAE Cliffortia 125 Acmadenia, Adenandra, Agathosma, Clausena, Coleonema, Diosma, Empleurum, Euchaetis, Macrostylis, RUTACEAE 254 Phyllosma, Sheilanthera

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Table S2.

Start Year Species Cumulative Species Taxonomists Species per Taxonomist 1755 30 40 2 14 1760 33 70 3 12 1765 40 103 4 10 1770 35 143 5 7 1775 37 177 6 6 1780 38 214 6 6 1785 48 252 6 8 1790 30 301 7 5 1795 52 331 8 6 1800 63 383 10 6 1805 74 445 11 7 1810 43 519 10 4 1815 31 563 10 3 1820 27 593 11 2 1825 44 620 15 3 1830 94 664 17 6 1835 106 759 14 8 1840 96 865 12 8 1845 41 961 9 5 1850 31 1002 8 4 1855 44 1033 6 8 1860 57 1077 7 9 1865 44 1134 6 7 1870 24 1177 5 4 1875 9 1201 3 3 1880 11 1210 3 4 1885 15 1221 5 3 1890 35 1236 7 5 1895 48 1271 11 4 1900 46 1318 10 5 1905 42 1365 10 4 1910 35 1407 8 4 1915 39 1442 9 4 1920 39 1481 9 4 1925 53 1520 10 5 1930 47 1573 9 5 1935 40 1620 9 4 1940 45 1660 9 5 1945 68 1705 8 9 1950 57 1773 6 8 1955 62 1830 5 10 1960 48 1892 5 8 1965 63 1940 7 9 1970 47 2003 6 7 1975 48 2050 8 6 1980 73 2098 11 7 1985 76 2170 13 6 1990 70 2247 12 5 1995 38 2316 10 4 2000 31 2354 10 3 2005 27 2385 9 3

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