Division of Biology, Faculty of Science, University of Zagreb
Abstract
The restricted distribution of endemic plant species in the Northern Limestone Alps is commonly explained by a severe loss of biotypes and genetic plasticity during Pleistocene glaciation. In the present paper we examine the ecological features of the regional endemic species and plant communities to see if they actually support this interpretation. In particular, we focus on (1) species composition and habitat characteristics of endemic plant communities, (2) the frequency of endemic species in different plant communities and habitat types, (3) the correlation between the frequency of endemic species and the density of the vegetation cover and (4) the altitudinal distribution of endemic species. Concerning endemic plant communities, there is considerable variation in species composition as well as in habitat requirements. Communities of rock, scree and snowbed habitats are characterised by the predominance of endemic or subendemic species, whereas endemic alpine grassland types contain mainly non-endemic plants.
Regarding the distribution of endemic plants, no uniform trend could be detected. The endemic species pool contains plants restricted to azonal stands as well as typical species of climax grasslands and widespread generalists. Some endemics distinctly prefer open vegetation types, others predominantly occur in dense grasslands. The bulk of the species considered performs best in the lower alpine zone, some others are especially common in the subalpine zone, whereas only one species showed an occurrence peak in the upper alpine belt. In summary, it may be said that the habitat requirements of endemic plants are rather species-specific and that there are only a few general trends. This fact seems to indicate the complex nature of the phenomenon of regional endemism, which is influenced by a range of factors. The prevailing historical explanation may not be appropriate for every species. Hence, the consideration of current ecological conditions in addition to historical factors may provide a more comprehensive explanation of regional endemism