A matter of scale: apparent niche differentiation of diploid and tetraploid plants may depend on extent and grain of analysis

Abstract

AimEmerging polyploids may depend on environmental niche shifts for successful establishment. Using the alpine plant Ranunculus kuepferi as a model system, we explore the niche shift hypothesis at different spatial resolutions and in contrasting parts of the species range.LocationEuropean Alps.MethodsWe sampled 12 individuals from each of 102 populations of R. kuepferi across 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.ResultsAll 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.Main conclusionsAlthough 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.

Habitats on the grid: The spatial dimension does matter for red-listing

“…In theory, any scale can be used to study ecological problems, and no specific spatial scale may be universally applied; nevertheless, the scale at which environmental patterns are quantified influences the result (Brandt, 1998;Turner et al, 2001;Wiens, 1989;Wu, 2004) and inappropriate scales may fail in detecting patterns (Li & Wu, 2004;Kirchheimer et al, 2015). With increasing grain size (and decreasing scale), units which are intrinsically rare or naturally occur as very small stands may become less represented or even disappear (Turner et al, 2001).…”

Correlations of polyploidy and apomixis with elevation and associated environmental gradients in an alpine plant

“…Self-fertility of tetraploids supported the assumption of Baker’s law that rapid colonization could have played a role in distributions (Cosendai et al , 2013). Recently, Kirchheimer et al (2016) found a niche shift between diploid and tetraploid cytotypes, mostly towards lower temperatures, but it remained unclear whether this shift actually correlates to mode of reproduction or to other physiological features connected to polyploidy. Shifts to lower temperatures in high elevations and northern latitudes are often connected to special morphological adaptations, like small growth form (alpine dwarfism), which is mostly due to slower cell cycle and cell differentiation processes (Körner, 2003).…”

“…Kirchheimer et al (2016) hypothesized that the observed niche shift may not be the decisive factor, but rather consequence of a rapid colonization process, which was enhanced by the ability of rapidly founding populations via apomixis. In the case of frequent founder events after long distance dispersal, apomictic seed production should be most frequent in the marginal populations of the distribution range.…”

“…temperature and precipitation? A more comprehensive study on the effects of climate factors and niche dynamics on cytotypes has been presented elsewhere (Kirchheimer et al , 2016). …”

Do floral and niche shifts favour the establishment and persistence of newly arisen polyploids? A case study in an Alpine primrose

“…about 1 Â 1 km) spatial resolution (Hijmans et al, 2005) for the south-western Alps. Because (micro-)topographic features can strongly affect climate in Alpine habitats (Körner, 2003) and because the resolution of the environmental layer used in modelling may affect model prediction (Guisan et al, 2007;Randin et al, 2009;Kirchheimer et al, 2016), we employed a finer spatial resolution. The coarse-scale (1 km resolution) climatic grids were statistically down-scaled to 100 m resolution, following the approach detailed in Zimmermann et al (2007).…”