BACKGROUND AND AIMS: Ecological differentiation is recognized as an important factor for polyploid speciation, but little is known regarding whether the ecological niches of cytotypes differ between areas of sympatry and areas where single cytotypes occur (i.e. niche displacement). METHODS: Ecological niches of four groups of Senecio carniolicus sensu lato (s.l.) (western and eastern diploid lineages, tetraploids and hexaploids) were characterized via Landolt indicator values of the accompanying vascular plant species and tested using multivariate and univariate statistics. KEY RESULTS: The four groups of S. carniolicus s.l. were ecologically differentiated mainly with respect to temperature, light and soil (humus content, nutrients, moisture variability). Niche breadths did not differ significantly. In areas of sympatry hexaploids shifted towards sites with higher temperature, less light and higher soil humus content as compared with homoploid sites, whereas diploids and tetraploids shifted in the opposite direction. In heteroploid sites of tetraploids and the western diploid lineage the latter shifted towards sites with lower humus content but higher aeration. CONCLUSIONS: Niche displacement can facilitate the formation of stable contact zones upon secondary contact of polyploids and their lower-ploid ancestors and/or lead to convergence of the cytotypes' niches after they have attained non-overlapping ranges. Niche displacement is essential for understanding ecological consequences of polyploidy.

Department of Botany and Biodiversity Research University of Vienna Rennweg 14 A 1030 Vienna Austria

Department of Botany and Biodiversity Research University of Vienna Rennweg 14 A 1030 Vienna Austria GLORIA co ordination University of Natural Resources and Life Sciences Vienna Center for Global Change and Sustainability and Austrian Academy of Sciences Institute for Interdisciplinary Mountain Research Silbergasse 30 3 A 1190 Vienna Austria

Department of Botany and Biodiversity Research University of Vienna Rennweg 14 A 1030 Vienna Austria Vienna Institute for Nature Conservation and Analyses Giessergasse 6 7 A 1090 Vienna Austria

Department of Botany Faculty of Science Charles University Prague Benátská 2 Prague CZ 128 01 Czech Republic and Institute of Botany The Czech Academy of Sciences Průhonice 1 CZ 252 43 Czech Republic

Institute of Botany University of Innsbruck Sternwartestrasse 15 A 6020 Innsbruck Austria

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