DOI: 10.5061/dryad.5r62f
title: Data from: Changes in assembly rules along a stress gradient from open dry grasslands to wetlands

description: A central issue of community ecology is finding rules that explain the
 composition and abundance of co-existing species. Nowadays two main
 processes, environmental filtering and limiting similarity are thought to
 play the main roles in structuring communities. Their relative importance
 under different environmental conditions, however, is still not properly
 clarified. We studied the strength and the effect of environmental
 filtering (causing convergence) and limiting similarity (causing
 divergence) in 137 sample plots along an extremely long environmental
 gradient ranging from open sand grasslands to highly productive marshes,
 using a trait based approach. The main environmental gradient (i.e.
 productivity) was characterised by the Normalized Difference Vegetation
 Index, an indicator of aboveground live biomass. Cover of the plant
 species was estimated visually. Values of 11 plant traits were collected
 from field measurements and databases. Mean and dispersion of the trait
 values of the plots were quantified by community-weighted means and
 Rao's quadratic entropy. Trait convergence and divergence were tested
 by randomization tests, followed by the study of changes in effect size
 along the productivity gradient by fitting generalized additive mixed
 models (GAMM). For vegetative traits we found mainly convergence,
 indicating the filtering effect of environmental constraints, while traits
 related to regeneration showed divergence. The strength of convergence in
 vegetative traits generally decreased as productivity grew, indicating
 that while under harsh conditions environmental constraints strongly limit
 the possible trait values; under more benign conditions various water and
 nutrient-use strategies are adaptable. At high productivity, the strength
 of divergence in regenerative traits decreased. Since the larger diversity
 of vegetative traits found here reduces competition, the importance of
 diverse reproductive strategy is probably lower. Synthesis: Our results
 partly support the stress-dominance hypothesis, but reveal that assembly
 rules are more complex. The relative importance of environmental filtering
 and limiting similarity depends on the trait and on the environmental
 conditions of the habitat. Traits related to resource use are generally
 limited by environmental filtering, and this restriction is weakening as
 conditions become more favourable, while traits related to regeneration
 are constrained by limiting similarity and are more diverse under harsh
 conditions.
description: Data files and
 supplementary materialsThe file contains the
 data files used in the analyses, and the supplementary materials. The
 „plot_NDVI.csv” file contains the Normalised Difference Vegetation Index
 (NDVI) values of the sample plots, the „plot_species.csv” contains the
 percentage cover of the species in the sample plots, the
 „species_trait.csv” contains trait values of the species found in the
 plots. The following traits were used: plant growth form, age of first
 flowering, clonal height, leaf size, specific leaf area, leaf dry matter
 content, lateral spread, plant life span, leaf distribution, shoot growth
 form, seed weight and seed bank type. Files
 "FigS1_SuppInf_location.pdf", "FigS2_SuppInf_trait
 variance.pdf", "FigS3_SuppInf_spider plots.pdf",
 "FigS4_SuppInf_right skewness of distribution.pdf" and
 "FigS5_SuppInf_lateral spread.pdf" contains supplementary
 materials. For more detailed information about the data and the
 abbreviations used in the tables and figures, see
 ReadMe.txt.assembly rules_productivity
 gradient.zip