DOI: 10.5061/dryad.d24c7
title: Data from: Environmental conditions and biotic interactions acting together promote phylogenetic randomness in semi-arid plant communities: new methods help to avoid misleading conclusions

description: QUESTIONS: Molecular phylogenies are increasingly used to better
 understand the mechanisms structuring natural communities. The prevalent
 theory is that environmental factors and biotic interactions promote the
 phylogenetic clustering and over-dispersion of plant communities,
 respectively. However, both environmental filtering and biotic
 interactions are very likely to interact in most natural communities,
 jointly affecting community phylogenetic structure. How do environmental
 filters and biotic interactions jointly affect the phylogenetic structure
 of plant communities across environmental gradients? LOCATION: Eleven
 Stipa tenacissima L. grasslands located along an environmental gradient
 from central to southeast Spain, covering the core of the distribution
 area of this vegetation type in Europe. METHODS: We jointly evaluated the
 effects of environmental conditions and plant–plant interactions on the
 phylogenetic structure – measured with the mean phylogenetic distance
 index of the studied communities. As an indicator of environmental
 conditions, we used a PCA ordination including eight climatic variables.
 Different metrics were used to measure the following processes: (1)
 competition/facilitation shifts at the entire community level (species
 combination index), and (2) the effect of microclimatic amelioration
 provided by the two most important nurse plants on neighbour composition
 (similarity indices and comparison of the phylogenetic pattern between
 canopy patches and bare ground areas). RESULTS: Biotic interactions and,
 to a less extent, environmental conditions affected the phylogenetic
 pattern of the studied communities. While positive plant–plant
 interactions (both at community level and the scale of individual nurse
 plants) increased phylogenetic overdispersion, higher rainfall increased
 phylogenetic clustering. The opposing effects of environmental conditions
 and biotic interactions could be the main cause of the overall random
 phylogenetic structure found inmost of these communities. CONCLUSIONS: Our
 results illustrate, for the first time, how an overall random phylogenetic
 pattern may not only be promoted by the lack of influence of either
 environmental filtering or biotic interactions, but rather by their joint
 and opposing effects. They caution about making inferences on the
 underlying mechanisms shaping plant communities from the sole use of their
 phylogenetic pattern. We also provide a comprehensive set of
 easy-to-measure tools to avoid misleading conclusions when interpreting
 phylogenetic structure data obtained from observational studies.
description: dataThis dataset aimed to
 assess the joint effect of the environment and plant-plant interactions in
 the phylogenetic pattern of semiarid plant communities. Data were obtained
 for 11 30 m x 30 m sites across a rainfall gradient in Spain. We assessed
 species co-occurrence at two different scales, at the site-level, using 80
 1.5 m x 1.5 m quadrats, and at the microsite-scale, using 30 0.5 m x 0.5 m
 quadrats beneath three different microsites (open areas, stipa tenacissima
 tussocks and quercus coccifera shrubs). From the data at the site-scale we
 obtained plant species richness, plant co-occurrence metrics (C-score,
 Species combination indices) and the phylogenetic pattern of the plant
 community. See associated article for further details. From the data at
 the patch-scale we obtained similarity indices and the phylogenetic
 pattern of those species that were more abundant beneath a nurse than in
 the open. The dataset was complemented with climatic data available in the
 literature (Ninyerola M, Pons X y Roure JM. 2005. Atlas Climático Digital
 de la Península Ibérica. Metodología y aplicaciones en bioclimatología y
 geobotánica. ISBN 932860-8-7. Universidad Autónoma de Barcelona,
 Bellaterra). More details in the data can be obtained both in the metadata
 spreadsheet in the Excel file. Empty data is in blank. There is only one
 empty space (MPDfac in the Camporreal site). Data was taken by S.
 Soliveres and F.T. Maestre, both authors of the associated paper. Contact
 for further information: Dr. Santiago Soliveres (e-mail:
 santiagosoliverescodina@gmail.com)Soliveres et al. JVS
 dryad.xls