title: A matter of scale: apparent niche differentiation of diploid and tetraploid plants may depend on extent and grain of analysis.
abstract: OBJECTIVE
  Emerging polyploids may depend on environmental niche shifts for successful establishment. Using the alpine plantRanunculus kuepferias a model system, we explore the niche shift hypothesis at different spatial resolutions and in contrasting parts of the species range.
  
  
  METHODS
  European Alps.
  
  
  METHODS
  We sampled 12 individuals from each of 102 populations ofR. kuepferiacross the Alps, determined their ploidy levels, derived coarse-grain (100 × 100 m) environmental descriptors for all sampling sites by downscaling WorldClim maps, and calculated fine-scale environmental descriptors (2 × 2 m) from indicator values of the vegetation accompanying the sampled individuals. Both coarse and fine-scale variables were further computed for 8239 vegetation plots from across the Alps. Subsequently, we compared niche optima and breadths of diploid and tetraploid cytotypes by combining principal components analysis and kernel smoothing procedures. Comparisons were done separately for coarse and fine-grain data sets and for sympatric, allopatric and the total set of populations.
  
  
  RESULTS
  All comparisons indicate that the niches of the two cytotypes differ in optima and/or breadths, but results vary in important details. The whole-range analysis suggests differentiation along the temperature gradient to be most important. However, sympatric comparisons indicate that this climatic shift was not a direct response to competition with diploid ancestors. Moreover, fine-grained analyses demonstrate niche contraction of tetraploids, especially in the sympatric range, that goes undetected with coarse-grained data.
  
  
  CONCLUSIONS
  Although the niche optima of the two cytotypes differ, separation along ecological gradients was probably less decisive for polyploid establishment than a shift towards facultative apomixis, a particularly effective strategy to avoid minority cytotype exclusion. In addition, our results suggest that coarse-grained analyses overestimate niche breadths of widely distributed taxa. Niche comparison analyses should hence be conducted at environmental data resolutions appropriate for the organism and question under study.
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, 1030 Vienna, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kirchheimer
authors.affiliation: Department of Systematics, Biodiversity and Evolution of Plants, Georg-August-University of Göttingen, 37073 Göttingen, Germany.
authors.forename: Christoph C F
authors.initials: CC
authors.lastname: Schinkel
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, 1030 Vienna, Austria.
authors.forename: Agnes S
authors.initials: AS
authors.lastname: Dellinger
authors.affiliation: Department of Systematics, Biodiversity and Evolution of Plants, Georg-August-University of Göttingen, 37073 Göttingen, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Klatt
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, 1030 Vienna, Austria.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Moser
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, 1030 Vienna, Austria; GLORIA co-ordination, University of Natural Resources and Life Sciences Vienna, Center for Global Change and Sustainability, Vienna, Austria; Institute for Interdisciplinary Mountain Research, Austrian Academy of Sciences, Innsbruck, Austria.
authors.forename: Manuela
authors.initials: M
authors.lastname: Winkler
authors.affiliation: UR Ecologie et Dynamique des Systèmes Anthropisés (EDYSAN, FRE 3498 CNRSUPJV), Jules Verne University of Picardie, F-80037 Amiens Cedex 1, France.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lenoir
authors.affiliation: Department of Biosciences, University of Milan, 20133 Milan, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Caccianiga
authors.affiliation: Department of Ecology and Evolution, University of Lausanne,, Switzerland; Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland.
authors.forename: Antoine
authors.initials: A
authors.lastname: Guisan
authors.affiliation: Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, MD 21532, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Nieto-Lugilde
authors.affiliation: Section for Ecoinformatics & Biodiversity, Department of Bioscience, Aarhus University, DK-8000 Aarhus C, Denmark.
authors.forename: Jens-Christian
authors.initials: JC
authors.lastname: Svenning
authors.affiliation: Laboratoire d'Écologie Alpine (LECA), Université Grenoble Alpes, F-38000 Grenoble, France; Laboratoire d'Écologie Alpine (LECA), CNRS, GrenobleF-38000, France.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Thuiller
authors.affiliation: Institute of Earth Surface Dynamics, University of Lausanne,, Switzerland.
authors.forename: Pascal
authors.initials: P
authors.lastname: Vittoz
authors.affiliation: Vienna Institute for Nature Conservation and Analyses, 1090 Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Willner
authors.affiliation: Landscape Dynamics, Swiss Federal Research Institute WSL, Birmensdorf CH-8903, Switzerland; Department of Environmental Systems Science, Swiss Federal Institute of Technology ETH, CH-8092 Zürich, Switzerland.
authors.forename: Niklaus E
authors.initials: NE
authors.lastname: Zimmermann
authors.affiliation: Department of Systematics, Biodiversity and Evolution of Plants, Georg-August-University of Göttingen, 37073 Göttingen, Germany.
authors.forename: Elvira
authors.initials: E
authors.lastname: Hörandl
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, 1030 Vienna, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Dullinger
keywords: European Alps; Ranunculus kuepferi; alpine plants; apomixis; competition; indicator values; niche breadth; niche shift; polyploidization; spatial grain