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Auteur Rolf Holderegger (1965-) |
Documents disponibles écrits par cet auteur (5)
Affiner la rechercheFactors determining bryophyte species richness and community composition on insular siliceous erratic boulders in calcareous landscapes / Daniel Hepenstrick in Journal of vegetation science, 32 (2021)
Titre : Factors determining bryophyte species richness and community composition on insular siliceous erratic boulders in calcareous landscapes Type de document : Imprimé Auteurs : Daniel Hepenstrick ; Ariel Bergamini ; Clare Webster ; Christian Ginzler ; Rolf Holderegger (1965-) Année de publication : 2021 Article en page(s) : 1-15 Langues : Français (fre) Catégories : [CBNPMP-Thématique] Bryophytes Résumé : Aim: Pleistocene erratic boulders are rocks that were relocated by glaciers during the Ice Ages. When their geology differs from the geology of the landscape that surrounds them, erratic boulders form habitat islands for regionally rare, edaphically specialised, rock-dwelling cryptogams (bryophytes, ferns and lichens). Such boulders constitute terrestrial model systems for exploring island biogeographic predictions and the effect of environmental variables on species diversity and community composition, which we studied in order to provide basic knowledge of the ecology, with relevance for the conservation, of these unusual island systems.
Location: Siliceous erratic boulders in the calcareous Swiss Plateau and Jura Mountains.
Methods: For 160 erratic boulders we recorded all bryophyte species and a diverse set of environmental variables. For all species and for specialist species acidophile rock-dwellers) separately, we analysed species–area relationships and nestedness, and explored relationships between environmental variables, species diversity and community composition.
Results: We found 138 bryophyte species, 19 of which were specialists of erratic boulders. A steeper species–area curve for boulder specialists than for total species richness underlined the island properties of boulders for specialist species. Large boulders were more likely to harbour numerous boulder specialists and communities on small boulders were nested within the communities present on large boulders. However, at the landscape level small boulders contributed more specialist species than a few large boulders of the same surface area. Erratic boulders near settlements were less likely to harbour boulder specialists. Boulders in open land harboured different and more specialist species than boulders in forests.
Conclusions: Large undisturbed erratic boulders in open land harbour rare bryophyte communities with a large number of specialist species. Conservation should thus prioritise this type of boulders. Furthermore, conserving large boulders is logistically easier, and they may function as flagships for small boulders that also contribute to the biodiversity within landscapes.Lien pérenne : DOI : 10.1111/jvs.13094 Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=147555
in Journal of vegetation science > 32 (2021) . - 1-15Hepenstrick, Daniel, Bergamini, Ariel, Webster, Clare, Ginzler, Christian, Holderegger, Rolf (1965-) 2021 Factors determining bryophyte species richness and community composition on insular siliceous erratic boulders in calcareous landscapes. Journal of vegetation science, 32: 1-15.Documents numériques
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Article (2021)URL
Titre : Floral free fall in the Swiss lowlands: environmental determinants of local plant extinction in a peri-urban landscape Type de document : Imprimé Auteurs : Ivana Stehlik (1971-) ; John P. Caspersen ; Lea Wirth ; Rolf Holderegger (1965-) Année de publication : 2007 Article en page(s) : 734-744 Langues : Anglais (eng) Catégories : [CBNPMP-Thématique] Messicole
[CBNPMP-Géographique] SuisseRésumé : Local floras are being depleted by a host of human activities, including habitat destruction and fragmentation, eutrophication, and the intensification of agriculture. Species with particular ecological demands or life-history attributes are more prone to extinction than species with a broader niche. We used an old herbarium from the municipality of Küsnacht (Swiss lowlands) as a historical record for comparison with contemporary plant diversity. This comparison revealed that 17% to 28% of all vascular plants that occurred between 1839 and 1915 were extinct by 2003. Species of different habitats and life-forms had significantly different rates of extinction: wetlands, disturbed sites and meadows lost most species, whereas forests and rocky habitats were least affected; aquatics and annuals were most prone to extinction, geophytes and hemicryptophytes were intermediate, and phanerophytes and chamaephytes were least affected. Species adapted to nutrient-poor soils suffered highest extinction in all habitats, indicating that eutrophication poses an urgent threat to species diversity. Light and soil moisture requirements also had significant effects on extinction, but the direction of the effect varied by habitat. When species were grouped into IUCN categories of the red list of Switzerland, the rank order of the observed extinction matched the red list assignment. Because many of the remaining species had high estimated extinction probabilities and because extinction is often delayed (extinction debt), a substantial part of the remaining flora of Küsnacht is likely to go extinct in the near future. This will increase the dominance of the common species that already comprise 81% of the local flora. The rates and patterns of extinction in Küsnacht are probably representative of surrounding Swiss lowlands and peri-urban landscapes in most developed countries. Studies such as ours can serve as a call for action and form a basis for future monitoring of biodiversity.
Lien pérenne : DOI : 10.1111/j.1365-2745.2007.01246.x Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=148480
in Journal of ecology > 95 (4) (July 2007) . - 734-744Stehlik, Ivana (1971-), Caspersen, John P., Wirth, Lea, Holderegger, Rolf (1965-) 2007 Floral free fall in the Swiss lowlands: environmental determinants of local plant extinction in a peri-urban landscape. Journal of ecology, 95(4): 734-744.Documents numériques
Article (2007)URL
Titre : Reproduction of the rare monocarpic species Saxifraga mutata L. Type de document : Imprimé Auteurs : Rolf Holderegger (1965-) Année de publication : 1996 Article en page(s) : 301-313 Langues : Français (fre) Mots-clés : Saxifraga sp. Résumé : The aim of the study is to investigate the impact of reproduction and genetic variation on the persistence of populations of the prealpine, monocarpic Saxifraga mutata L. The species grows on erosion slopes or rocks, and its local populations are often small and isolated. Crossing experiments resulted in better seed-set than selfing, but both yielded viable seeds. Agamospermy did not occur. In an early-successional species like S. mutata, successful selfing is important in the colonization of new habitats. Flowers of S. mutata were visited by Syrphidae and unspecialized Hymenoptera. A germination rate of 40% was reached in cultivation after 20 weeks but germination continued until the end of the experiment after 92 weeks. Seeds stored dry for 30 months at room temperature mostly lost their germinability. In natural habitats, seedlings were found almost throughout the year with a peak in spring. Suitable safe sites were small patches of open soil, bare marl on erosion slopes, and rock crevices. AU individuals investigated were diploid with 2n = 26. Allozyme electrophoresis showed a lack of segregation within the populations. Intra- and interpopulation genetic variation was low. These results were in partial disagreement with theoretical expectations in a mixed mating species. It is concluded that demographic rather than genetic processes are the main cause of extinction of populations of S. mutata, at least in the short-term. Lien pérenne : DOI : 10.1111/j.1095-8339.1996.tb02078.x Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=137895
in Botanical journal of the Linnean Society > 122 (4) (1996) . - 301-313Holderegger, Rolf (1965-) 1996 Reproduction of the rare monocarpic species Saxifraga mutata L. Botanical journal of the Linnean Society, 122(4): 301-313.Documents numériques
Article (1996)URL
Titre : Spatial genetic structure and clonal diversity of Anemone nemorosa in late successional deciduous woodlands of Central Europe Type de document : Imprimé Auteurs : Ivana Stehlik (1971-) ; Rolf Holderegger (1965-) Année de publication : 2000 Article en page(s) : 424-435 Langues : Anglais (eng) Mots-clés : Anemone sp. Note de contenu : 1 We tested whether established populations in similar environmental conditions exhibit similar or varying spatial genetic structures by comparing populations of the long-lived species Anemone nemorosa from a number of late successional deciduous woodlands in Central Europe. We discuss the ways in which genetic structure may have been shaped by clonal growth and sexual reproduction. 2 A standardized sampling strategy was used to collect 30 ramets from each of 20 populations. Genotypes of the samples were determined by allozyme electrophoresis and analysed assuming that A. nemorosa shows tetraploid-tetrasomic inheritance. 3 Genetic variation and clonal diversity were high compared with other clonal species. Most (95%) of the sampled ramets had unique multilocus genotypes with only 22 examples occurring more than once. Differences between observed and expected heterozygosities within populations were generally small to moderate. Fixation indices (mean of over 14 loci) in the populations ranged between 0.08 and 0.56 (grand mean = 0.21) confirming reports that the breeding system in A. nemorosa is predominantly outcrossing or mixed-mating. 4 Limited historic gene flow among populations (Nm = 0.62) was reflected by high population differentiation (GST = 0.29), low genetic identities among populations and a non-significant correlation between these identities and geographical distances. 5 Spatial autocorrelation (Moran’s I) showed no significant differences in genetic structures between populations under similar environmental conditions. Samples taken less than 0.5 m apart were genetically more closely related than to more distant samples, but similarity of genotypes decreased only slightly with further increase in distance. 6 The high levels of genetic variation found in populations of A. nemorosa are probably due to repeated seedling recruitment and the outcrossing or mixed-mating breeding system, whereas vegetative propagation and short-distance seed dispersal may contribute to the positive genetic autocorrelation observed at a small spatial scale.
Lien pérenne : DOI : 10.1046/j.1365-2745.2000.00458.x Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=137830
in Journal of ecology > 88 (3) (2000) . - 424-435Stehlik, Ivana (1971-), Holderegger, Rolf (1965-) 2000 Spatial genetic structure and clonal diversity of Anemone nemorosa in late successional deciduous woodlands of Central Europe. Journal of ecology, 88(3): 424-435.Documents numériques
Article (2000)URLUnderstanding population history for conservation purposes: population genetics of Saxifraga Aizoides (saxifragaceae) in the lowlands and lower mountains North of the Alps / Eva Lutz (2000)
Titre : Understanding population history for conservation purposes: population genetics of Saxifraga Aizoides (saxifragaceae) in the lowlands and lower mountains North of the Alps Type de document : Tiré à part de revue Auteurs : Eva Lutz ; Johann Jakob Schneller (1942-) ; Rolf Holderegger (1965-) Année de publication : 2000 Importance : 583-590 Langues : Anglais (eng) Catégories : [CBNPMP-Thématique] Distribution de la diversité génétique
[CBNPMP-Thématique] Histoire de la végétation, paléoécologieMots-clés : Saxifraga aizoides L. Résumé : Several alpine species have outlying populations in the lowlands and lower mountains north of the Alps. These small, isolated populations are usually described as either (1) glacial relics, (2) descendants from populations living on forelands and moraines during the ice ages, or (3) populations founded by long-distance dispersal after glaciation. A floristic survey of the historic and present distributions and an allozyme investigation were performed on one of these relic species, Saxifraga aizoides. The species was historically more abundant and had more stations in more regions of northeastern Switzerland. The former population structures within regions, nowadays destroyed, were still reflected in distinct and high regional genetic diversity and variation. There was weak evidence of increased inbreeding in outlying populations, but populations did not deviate from Hardy-Weinberg equilibrium. No geographic pattern of genetic variation above the regional scale (>10 km) was found. Based on the spatial and genetic structures found, it was not possible to discriminate between the abovementioned hypotheses. Nevertheless, the study shows how a thorough evaluation of distribution and abundance data aids the interpretation of genetic data with respect to population history, biogeography, and conservation biology. Lien pérenne : DOI : 10.2307/2656602 Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=131399 Lutz, Eva, Schneller, Johann Jakob (1942-), Holderegger, Rolf (1965-) 2000 Understanding population history for conservation purposes: population genetics of Saxifraga Aizoides (saxifragaceae) in the lowlands and lower mountains North of the Alps. American Journal of Botany, 87(4) : 583-590.Documents numériques
Article (2000)URL
