Habitat differentiation between two closely related Mediterranean plant species, the endemic Cyclamen balearicum and the widespread C-repandum

Ecological characteristics and habitat differences of two congeneric plant species were quantified in a survey of 19 ecological variables linked to climate, topography, soil and vegetation at 125 sites. One of these species, Cyclamen balearicum (Primulaceae), is endemic to the Balearic Islands and southern France, the other, C. repandum, is more widely distributed across the Mediterranean basin. The study area comprises the entire distribution of C. balearicum and the adjacent zones of Corsica and southern mainland France where C. repandum occurs. The two species have allopatric distributions, although in one very limited area within the geographic distribution of C. repandum, hybrid populations are thought to occur and in which pure C. balearicum is not present. We have found that there is little ecological overlap between C. repandum and C. balearicum sites. C. repandum is primarily a species of forest and woodland, either deciduous or evergreen, established on a large range of bedrock types, and with an important litter cover. In contrast, C. balearicum occurs almost exclusively in evergreen shrublands and open woodlands on rocky limestone substrates. These results are consistent with the frequent occurrence of endemic plant species in harsh habitats with low vegetation. Our data suggest that the endemic C. balearicum has narrower ecological amplitude than its widespread congener C. repandum. The habitat of hybrid populations on Corsica is within the range of habitats occupied by C. balearicum and is distinct from the habitats on Corsica where pure C. repandum populations occur. Populations of C. balearicum, now introgressed with C. repandum, may thus have persisted in ecologically suitable sites on Corsica, outside of the previously recognised geographic range for this species. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.