DOI: 10.5061/dryad.20mf5
title: Data from: Evolutionary relationships can be more important than abiotic conditions in predicting the outcome of plant-plant interactions

description: Positive and negative plant–plant interactions are major processes shaping
 plant communities. They are affected by environmental conditions and
 evolutionary relationships among the interacting plants. However, the
 generality of these factors as drivers of pairwise plant interactions and
 their combined effects remain virtually unknown. We conducted an
 observational study to assess how environmental conditions (altitude,
 temperature, irradiance and rainfall), the dispersal mechanism of
 beneficiary species and evolutionary relationships affected the
 co-occurrence of pairwise interactions in 11 Stipa tenacissima steppes
 located along an environmental gradient in Spain. We studied 197 pairwise
 plant–plant interactions involving the two major nurse plants (the
 resprouting shrub Quercus coccifera and the tussock grass S. tenacissima)
 found in these communities. The relative importance of the studied factors
 varied with the nurse species considered. None of the factors studied were
 good predictors of the co-ocurrence between S. tenacissima and its
 neighbours. However, both the dispersal mechanism of the beneficiary
 species and the phylogenetic distance between interacting species were
 crucial factors affecting the co-occurrence between Q. coccifera and its
 neighbours, while climatic conditions (irradiance) played a secondary
 role. Values of phylogenetic distance between 207–272.8 Myr led to
 competition, while values outside this range or fleshy-fruitness in the
 beneficiary species led to positive interactions. The low importance of
 environmental conditions as a general driver of pairwise interactions was
 caused by the species-specific response to changes in either rainfall or
 radiation. This result suggests that factors other than climatic
 conditions must be included in theoretical models aimed to generally
 predict the outcome of plant–plant interactions. Our study helps to
 improve current theory on plant–plant interactions and to understand how
 these interactions can respond to expected modifications in species
 composition and climate associated to ongoing global environmental change.
description: dataThis dataset aimed to
 assess the relative importance of evolutionary distance, dispersal
 mechanism and environmental conditions as drivers of plant-plant
 interactions in semiarid environments. For doing this, we sampled 11 Stipa
 tenacissima grassland communities along a climatic gradient spanning from
 the center to the southeast of Spain. Our study sites have annual
 precipitation and temperature values ranging from 273 mm to 488 mm and
 from 13°C to 17°C, respectively. Four environmental variables were
 collected for each site: irradiance, mean temperature, annual rainfall
 (collected from available climatic models, Ninyerola et al. 2005-Atlas
 Climático Digital de la Península Ibérica. Metodología y aplicaciones en
 bioclimatología y geobotánica. Univ. Autónoma de Barcelona, Bellaterra,
 Spain), and altitude. At each site we also evaluated particular pairwise
 interactions for the two dominant nurses in the study area (Q. coccifera
 shrubs and S. tenacissima tussocks) by using 0.5 m x 0.5 m quadrats (see
 associated article for further details). With this data, we obtained two
 indices, the RII (Armas et al. 2004-Ecology 85: 2682–2686) to evaluate the
 intensity of the interaction, and the Iimp (Seifan et al. 2010-J. Ecol.
 98: 356–361) to evaluate the importance of such pairwise interactions. To
 complement de dataset, phylogenetic distance between the two interacting
 species and the dispersal mechanism of the beneficiary species were also
 measured or obtained from available literature. More details from the
 dataset are given in the “metadata” spreadsheet and in the associated
 article). Related databases can be found in the dryad data package Data
 from: Environmental conditions and biotic interactions acting together
 promote phylogenetic randomness in semi-arid plant communities: new
 methods help to avoid misleading conclusions. Provisional DOI:
 doi:10.5061/dryad.d24c7. Gaps in the data are in blank. Field and
 dispersal mechanism data were collected by S. Soliveres and F.T. Maestre,
 the phylogenetic distances were calculated by R.Torices. Contact for
 further information: Dr. Santiago Soliveres (e-mail:
 santiagosoliverescodina@gmail.com)