2018 Endangered and ThreatenedCaribbean Species Naturalist of the Caribbean Region Special Issue No. 2 C.M.S. Carrington, R.D. Edwards, and G.A. Krupnick 2018 CARIBBEAN NATURALIST Special Issue No. 2:30–47 Assessment of the Distribution of Seed Plants Endemic to the Lesser Antilles in Terms of Habitat, Elevation, and Conservation Status C.M. Sean Carrington1,*, Robert D. Edwards2, and Gary A. Krupnick2 Abstract - The Lesser Antilles is part of the Caribbean biodiversity hotspot and a priority for conservation of its flora is its endemic taxa. Using data from herbarium specimen labels, we recently carried out a preliminary conservation assessment of the 263 seed plant taxa unique to these islands, reporting that 70% of them are potentially threatened. In an effort to make conservation recommendations for the threatened species, we have further analyzed the specimen data for patterns in their distribution. We found that just over ⅓ of the region’s endemics are restricted to a single island, and the majority of these are only found at a single location, whereas the others are found at multiple sites on each island. Diversity of regional endemics appears to be associated with larger islands, and while there appears to be a loose correlation between areas of high diversity of regional endemics and local endemism, there are a number of isolated centers of local endemism scattered across the island chain that may be of particular conservation concern. We also detected a relationship between diversity and elevation, with a peak in the number of endemic species occurred at mid- elevations (400–800 m). This correlation translates to a relationship between endemism and habitat type, with elevated numbers of endemics found in rainforest and elfin woodland, both communities that typically occur at mid- to high elevations, respectively. The high- est proportion of threatened taxa is found in restricted and fragmented communities (elfin woodland, summit-herb vegetation, river bank, and moist forest) and the lowest proportion is found in the largest, most contiguous community (rainforest). Focused conservation ac- tion should occur in these important areas where plant endemism is locally high and habitat types are restricted and fragmented. Introduction Despite the recognition of the Caribbean as a global biodiversity hot spot (Mit- termeier et al. 2004, Myers et al. 2000) there is limited information available on the conservation status of Caribbean plants (Maunder et al. 2011). An on-line, up-to- date, searchable database of the seed plants of the West Indies (Acevedo-Rodríguez and Strong 2017) is a strong contribution to Target 1 of the Global Strategy for Plant Conservation (GSPC), which calls for “an online flora of all known plants”, and we have begun to make progress in the Caribbean on GSPC Target 2, which calls for “an assessment of the conservation status of all known plant species, as far as 1Department of Biological and Chemical Sciences, The University of the West Indies, PO Box 64, Bridgetown, Barbados. 2Department of Botany, National Museum of Natural History, Smithsonian Institution, PO Box 37012, MRC-166, Washington, DC 20013-7012 USA. *Corresponding author - [email protected]. Manuscript Editor: Thomas Brandeis 30 2018 Caribbean Naturalist Special Issue No. 2 C.M.S. Carrington, R.D. Edwards, and G.A. Krupnick possible, to guide conservation action” (Convention on Biological Diversity 2010). An important part of targeted conservation is understanding the characteristics and distributions of the plants and biological communities at risk, as emphasized in GSPC Target 5, “At least 75 percent of the most important areas for plant diversity of each ecological region protected with effective management in place for conserv- ing plants.” Target 5 has 2 components: identifying the areas important for plant diversity and ensuring effective protection of at least 75% of these areas. Herbarium specimens are records of plant distribution in time and space, the more recent of which usually provide more information than the older, historic ones. Re- searchers are finding new uses for herbarium collections far beyond those for which they were originally intended, including conservation assessment and identifying areas important for the protection and preservation of different species (Nualart et al. 2017). Data from herbarium specimens have already contributed to preliminary global conservation assessments of the flora of Puerto Rico and the Virgin Islands (Miller et al. 2012, 2013) and, more recently, of the endemic seed plants of the Lesser Antilles (Carrington et al. 2017), both based on IUCN Red List Categories and Crite- ria (IUCN 2001). In the latter study, the focus was on Lesser Antillean endemic taxa (Acevedo-Rodríguez and Strong 2017) because these species are found nowhere else and so are prioritized when embarking on conservation work. This preliminary as- sessment of the 263 seed plant taxa endemic to the Lesser Antilles revealed some 70% of taxa were at risk (Carrington et al. 2017). In the present study, we carried out fur- ther analyses on the 263 seed plant taxa endemic to the Lesser Antilles (Appendix 1). Using the elevations and habitats recorded on specimen labels, we determined how threatened and non-threatened endemics are distributed ecologically and spatially, and generated maps of endemic-species richness and local endemism to identify areas and habitats that may be of conservation concern. Methods We prepared a list of 263 seed plants (248 species, 6 subspecies and 9 varieties in 73 families) endemic to the Lesser Antilles (as defined by Acevedo-Rodríguez and Strong [2008]: Anguilla, Antigua, Barbados, Barbuda, Dominica, Grenada, the Grenadines, Guadeloupe, Martinique, Montserrat, Nevis, Saba, St Barthélemy, St. Eustatius, St. Kitts, St. Lucia, St. Maarten/St. Martin, and St. Vincent) using the Flora of the West Indies database (Acevedo-Rodríguez and Strong 2017). We noted pertinent data (collector, specimen number, collection date, island, locality, habitat, elevation) from 6193 specimen labels of these taxa from 11 herbaria with important Lesser Antilles plant collections (see Carrington et al. 2017). We used the descriptions of habitat on the herbarium sheet labels to categorize specimens to 1 of 20 habitat types—open habitat, cultivated area, roadside, beach vegetation, coastal vegetation, mangrove, swamp, pond, river bank, grassland, scrub, thicket, forest (type unspecified), dry forest, moist forest, rainforest, forest border, elfin woodland, summit-herb vegetation, and fumarole. This classification system com- prises simple land-use categories and vegetation types derived from Beard’s (1949) system, which is widely recognized in the Caribbean. These categories were broad 31 2018 Caribbean Naturalist Special Issue No. 2 C.M.S. Carrington, R.D. Edwards, and G.A. Krupnick enough yet sufficiently clear-cut to be applied unequivocally to the habitat descrip- tions found on the specimens. We assigned each taxon to a habitat type based on the predominant habitat recorded on the specimen labels for that taxon. The one exception was when the generic term “forest” was the most common for a taxon, in which case we assigned the specimen to the type of forest that was next most- frequently recorded for that taxon. If a label did not include habitat information, we did not attempt to use our knowledge of localities to assign a specific habitat to the specimen. We determined mean elevation for each taxon using the elevations that were written on the specimen labels (56% of all specimens had elevation data). For speci- mens where the label described an elevation range, we based our calculation for that specimen on the median elevation. We also determined mean elevation for each taxon based on GPS elevation values calculated at 3 arc seconds using the Shuttle Radar Topography Mission (SRTM-1) digital elevation model (http://srtm.csi.cgiar. org/) for each georeferenced specimen. We did not calculate elevation values for specimens with vague locality information. We employed the results of a preliminary conservation assessment using the IUCN Red List Categories and Criteria (IUCN 2001) to rate taxa as threatened (critically endangered [CR], endangered [EN], or vulnerable [VU]), not threat- ened (near threatened [NT] or least concern [LC]), or data deficient (DD), as previously detailed (Carrington et al. 2017). We were working only with species already identified as endemic to the island group as a whole (“regionally endemic”); thus, we refer to patterns of range restric- tion within these species as “local endemism”. We carried out analyses of richness and local endemism on all endemic taxa, except 5 species with vague or no local- ity information (Calyptranthes boldinghii Urb., Croton martinicenis Urb., Cuphea crudyana Koehne, Metastelma martinicense Schltr., and Ocotea l’herminieri Mez). We georeferenced specimens as previously described (Carrington et al. 2017) and removed centroided data. We converted coordinates from WGS84 to UTM20 to minimize projection distortion. We aggregated records to 5-km edge grid-cells using Biodiverse v1.99_007 (Laffan et al. 2010) and calculated measures for cor- rected weighted endemism (CWE) and species richness. We used CWE to identify areas with a high representation of narrow-range taxa, and to pinpoint areas of high priority for conservation. We weighted species in a grid cell by the proportion of their ranges that the cell represented; the narrower the range, the higher the weight assigned to that species. We summed the weight and divided by the number of spe- cies in that cell to correct for richness and inflation of values due to many relatively wide-ranging species (Crisp et al. 2001, Laffan and Crisp 2003). We replicated these analyses for all regionally endemic species, threatened regional endemics only, and non-threatened regional endemics only. Results The geographical ranges of the 263 Lesser Antillean endemics vary consider- ably but with a noticeable inverse relationship between the number of species and 32 2018 Caribbean Naturalist Special Issue No. 2 C.M.S. Carrington, R.D. Edwards, and G.A.