588 A. ‐T. Valli et al.


&Erben, 2016; González-Orenga et al., 2021). The Limonium species of the Mediterranean area often have punctiform distributions (Brullo & Erben, 2016; Buira et al., 2017). Limonium species typically grow in littoral habitats, and


they are adapted to the environmental stress of rocky and sandy seashores and salt marshes (Erben, 1993; Caperta et al., 2014). However, a substantial number of these littoral species are threatened (van der Maarel & van der Maarel- Versluys, 1996), primarily as a result of anthropogenic impacts in coastal regions. Fourteen Limonium species endemic to Greece are already considered threatened (Phitos et al., 1995, 2009). The Greek Ionian Islands host 14 Limonium species, nine of which are endemic to this archipelago (Dimopoulos et al., 2013; Flora Ionica Working Group, 2016). Among these, three species (Limonium kora- konisicum R. Artelari & Valli, Limonium phitosianum R. Artelari and Limonium zacynthium R. Artelari) are en- demic to Zakynthos Island. The narrow ranges of the en- demic Limonium species in the Ionian Islands combined with the high vulnerability of their specialized habitats indicate the need for appropriate conservation measures. Here we combine demographic and genetic approaches


to assess conservation status and population trends, and predict the extinction risk of the three Limonium species endemic to Zakynthos Island. We aimed to (1) define the distribution of the species by exploring all potentially suit- able habitats, (2) assess their population dynamics and reproductive biology, (3) estimate genetic diversity and potential gene flow within and among subpopulations of L. phitosianum and L. zacynthium, and (4) propose conser- vation measures for the management and maintenance of the three species.


Methods


Studied species Limoniumkorakonisicum, L. phitosianumand L. zacynthium are endemic to Zakynthos Island (Plate 1). Although endem- ismin Limonium is usually associated with apomixis (Erben, 1978;Artelari, 1984a;Castro&Rosselló, 2007;Brullo&Erben, 2016),most of the Ionian endemics, including L. phitosianum and L. zacynthium, are sexually reproducing diploids (2n= 18; Artelari, 1984a,b; Artelari & Kamari, 1986). Other Limonium species are mostly polyploids and typically apo- mictic, and L. korakonisicum is the only endemic apomictic polyploid species (6×) known in this area (Valli & Artelari, 2015). The latter species forms a small population in the Korakonisi area, where it coexists with L. phitosianum (Valli &Artelari, 2015). Limonium phitosianum and L. zakynthium are included in The European Threatened Plant List (Sharrock & Jones, 2009). A record of L. phitosianum from the Stamfani islet in the Strofades Islands c. 46 km


south-south-east of Zakynthos (Brullo & Erben, 2016)is based on a single incomplete specimen (Messenien, Insel Stamfani, 14 September 1980,Piepers.n.(Herb.Greuter)), and its occurrence there is considered doubtful. All subse- quently collected Limonium specimens from Strofades Islands belong to Limonium virgatum (Willd.) Fourr., and therefore L. phitosianumis considered endemic to Zakynthos.


Geographical distribution and spatial data


To document distribution, we conducted a 5-year survey (2014–2018) encompassing all suitable habitats (i.e. calcar- eous maritime cliffs, rocky and sandy coastal areas) across Zakynthos Island. We mapped each species once per year, during flowering, using a GPS, and calculated extent of occurrence (EOO) for each species and the local extent of occurrence (local EOO) of each subpopulation using ArcGIS 10.5.1 (Esri, USA), and estimated area of occupancy (AOO) as the sum of the occupied 2 × 2 km grid cells per species (IUCN, 2022a). Estimated EOO and AOO were cross-checked using GeoCAT (Bachman et al., 2011). Local EOO was calculated following Andreou et al. (2011) as the smallest polygon or polygons encompassing all plant col- onies uninterrupted by unsuitable habitat at each subpopu- lation location. We chose this approach because a 2 × 2 km grid is too coarse for species with restricted geographical distributions, particularly littoral species, and provides a more precise measure of a species’ spatial extent within its fragmented habitats, often yielding smaller values than the traditional EOO. In 2023, we revisited the locations of all three species to ascertain whether there had been any changes in EOO or AOO since 2018.


Population size


The terminology used (mature individual, population, sub- population, population size and location) follows IUCN (2022a). To estimate population size, a count of all mature individuals was conducted during flowering and fruiting across all subpopulations of each species. For L. korakonisi- cum, we completely censused mature individuals in 5 con- secutive years (2014–2018; Table 1). For L. phitosianum,we counted mature individuals in 20 random 5 × 5 m plots in subpopulations Lp1,Lp2,Lp8,Lp9 and Lp11, and in com- plete censuses in other subpopulations over the same 5- year period, except for Lp13 and Lp14 (only in 2018). For L. zacynthium, we counted mature individuals in four ran- dom 5 × 5 m plots in subpopulation Lz1, and in complete censuses in other subpopulations for the same 5 consecutive years, except for Lz2 and Lz3 (4 years of counts). The num- ber of plants per m2 provided an approximate estimate of plant density (Andreou et al., 2015), calculated by dividing the number of mature individuals by the local EOO for each subpopulation. To assess the stage-structure


Oryx, 2024, 58(5), 587–599 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324000140


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