Exploring the different facets of plant endemism in the South-Eastern Carpathians: a manifold approach for the determination of biotic elements, centres and areas of endemism

In the European Alpine System, the Carpathian Mountains are recognized as one of the major centres of diversity and endemism. In the present study, we aimed to explain the spatial structure of plant endemism in its South-Eastern subunit by the complementary use of diversity indices, parsimony analysis of endemicity (PAE), biotic element analysis (BEA), and barrier analysis. We analyzed the available information on 111 plant taxa confined to the South-Eastern Carpathians, mapped using two different sets of operational geographical units (OGUs): 71 geomorphological units and 64 quadrats. Our results showed that centres of endemics diversity largely corresponded to the areas of endemism and biotic elements. PAE consensus cladogram outlined four major areas of endemism (with three nested ones): (1) Danubian; (2) western part of the Southern Carpathians; (3) eastern part of the Southern Carpathians; and (4) Pocutico-Marmarossian. Out of the seven identified biotic elements, five were spatially clustered and overlapped the major areas of endemism, with one notable exception: the calcareous massifs from the Eastern Carpathians, not identified through PAE. Conversely, the latter outlined a nested area of endemism (Cozia - Buila-Vanturari?a), omitted by BEA. Barrier analysis identified three major breaks in the distribution of endemics: (1) south of the Retezat - ?arcu - Godeanu mountain group; (2) north of the Piatra Craiului - Bucegi - Ciucas mountain group; and (3) north of the Rodna massif. The results obtained in here using different methods are generally spatially convergent, indicating highly structured patterns of endemism in the South-Eastern Carpathians. These patterns mostly follow the present-day distribution of alpine habitats and calcareous bedrock, which might have acted as isolating factors through insularity. Interestingly, three of the spatial clusters of OGUs obtained from the endemics distribution analyses (the Eastern Carpathians, as well as eastern and western parts of the Southern Carpathians) largely also correspond to the mid-Miocene archipelago configuration of landmasses in this part of the Carpathians. This might suggest the existence of older migration barriers that emerged throughout the Neogene Period. Differences in the spatial patterns outlined by PAE and BEA could stem from partial sympatry of endemics caused by post-speciation processes such as dispersal or extinction. Additionally, sympatric distribution of taxa with disjunct populations may be caused by the absence of divergence among segregated populations, such as the patterns of relict distributions seen in alpine plants. Finally, the complementary use of these methods may prove to be an efficient approach for better understanding the geographical structure of endemism and provide a starting point for further testing of hypotheses on evolutionary processes.