Study area and focal species of edaphic islands
We selected 20 rocky (granite or syenite) outcrops occurring in the southern Czech Republic, located at elevations around 450 m a.s.l. (centroid: 49°14’12”N, 15°57’26”E; Figure 1). These outcrops (edaphic islands) are scattered across approximately 100 km2and embedded in a landscape matrix of arable land. Their average area is ~2,912 m2 (min = 361 m2, max = 14,115 m2). The regional macroclimate is temperate (mean annual temperature: 6.5–8°C, annual precipitation: 500–550 mm; Tolasz, 2007), characterized by a marked temperature and precipitation seasonality (Doležal et al., 2021). The vegetation growing on these gently dome-shaped outcrops (maximum elevation ~5-10 m compared to the surroundings) is acidophilous dry grassland.