FIGURE 1 (a) Map and geographical location of the edaphic islands on rocky outcrops in the Czech Republic, Central Europe (red-filled circle in the inset); black-filled circles correspond to the studied edaphic islands, while the white circles represent all the edaphic islands in the surrounding landscape. (b) Example of one edaphic island embedded in the agricultural landscape, and (c) a closer look at the studied shallow-soil, acidophilous temperate dry grassland. Photo credit: FE Méndez-Castro.
We focused on 13 perennial plant species confined to the discrete outcrop grasslands, constituting ~45% of the total number of specialist species of this vegetation type (Méndez-Castro et al., 2021). These specialist species should be: 1) adapted to the harsh environment of rocky outcrops (especially concerning the putatively strong edaphic filter), and 2) more affected by insularity than non-specialists (for which the surrounding landscape should not be as inhospitable; Conti et al., 2021; Méndez-Castro et al., 2021). The selected species belong to different plant functional types (9 forb species, 2 chamaephytes, 1 grass, 1 sedge), and life histories (5 clonal, 8 non-clonal species). The clonal species are Carex caryophyllea, Cerastium arvense, Hieracium pilosella, Koeleria macrantha, and Trifolium alpestre , whereas the non-clonal species are Carlina acaulis, Centaurea stoebe, Helianthemum grandiflorum subsp. obscurum, Knautia arvensis, Lychnis viscaria, Scleranthus perennis, Silene nutans, and Thymus pulegioides . Hereafter, we refer to these species using their genus name. Species were found in the majority of the edaphic islands (i.e. 12 to 20 islands), except for Helianthemum (6) and Carex (9).