Die Rolle von Fels-Habitaten für Nischenkonstanz und als Refugien für Pflanzen : drei Fallstudien
Numerous phylogenetic studies look for speciation without ecological radiation (PNC = phylogenetic niche conservatism). However, they ask only rarely for the role of the habitats for niche constancy. Starting from the hypothesis of DAVIS (1951) and SNOGERUP (1971) that the rock environment is 1) an evolutionary trap, conserving many old lineages (phylogenetic relicts) and that 2) it serves as a refugium under climate change, the rock vegetation is analysed for relic-tic species and niche conservatism. Three case studies, based upon phytosociological data sets from subtropical Africa, the Mediterranean area and the Eastern Alps are analysed. Molecular phylogenetic trees from selected taxa indicate the time of the splitting of lineages and the dura-tion of niche constancy. The comparison of succulent communities on rocks in SW-Arabia (class Kleinio-Carallumetea) and on the Canary Islands (Kleinio-Euphorbietea) shows numerous vicarious taxa (synvicariism). The phylogenetic tree of Campylanthus allows assuming the origin of this vicariance pattern in a geo-graphical separation of the ancestors in Mid Tertiary. The aridisation of Northern Africa about 6 Mya ago resulted in this high distance disjunction between Macaronesia and the Eritreo-Arabian region. The separated taxa underwent allopatric speciation, without ecological radiation. They remained in their niches. The vegetation of halve-caves with soaking water (class Adiantetea capilli-veneris) in the Mediterra-nean area and adjacent subtropics shelters local endemics, forming a mosaic of vicarious species. They belong to the genus Pinguicula in the NW-Mediterranean, to Hypericum (section Adenosepalum) in the SW-Mediterranean, and to Primula subgenus Sphondylia on the Arabian Peninsula and its surroundings. These vicariance patterns date back to the Late Tertiary and the climatic conditions in the Quaternary. The constant water supply - quite independent from the macroclimatic condi-tions - and the stenothermic rock surface favour in-situ resilience and make the Adiantetea to outstanding refugia for phylogenetic and geographical relicts. The example of the Caricetum firmae demonstrates relict phenomena, dating back to the last ice age. The rock fissures and calciphilous, alpine rock turfs of the massifs fringing the Eastern Alps shelter endemic cushion plants from genera such as Potentilla, Primula, Androsace, and Gentiana. These taxa of low dispersal capacity are still located in their glacial refugia. The actual species combination of rock communities mirrors historical events. The floristic and spatial patterns are influenced by former climatic conditions, by evolutionary processes and by dispersal limitations. Because of the high variety of micro-habitats, rocks offer refugia and shelter relicts. It is a habitat of outstanding niche conservatism, resulting in patterns of vicarious species and parallel evolution.
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