DOI: 10.5061/dryad.j0zpc86n5
title: Large-scale facilitative effects of Vachellia caven

description: The importance of nurse plants structuring plant communities is well
 appreciated at local scales, yet the effect of a single nurse on large
 scales has been neglected in analyses. So far, studies only use
 environmental gradients within one type of ecosystem and tend to
 generalize the nurse effects. To assess how the effect of a single nurse
 species is modulated by different environmental settings, interactions
 between the shrub Vachellia caven and the surrounding plant communities
 were evaluated at 481 paired plots (outside vs underneath the plant
 crown), in 39 sites across two distribution ranges, the Mediterranean west
 and the mostly subtropical east of the Andes mountains (covering ca. 2x10
 6 km2). Cover, abundance, and richness of perennial plants underneath and
 outside V. caven were used as response variables to estimate an index
 indicative of plant interactions (RII) and tested how this was affected by
 the rainfall gradient and distribution range. Overall, RII responses to
 rainfall gradients had low conditional R2 (~0.25) at this large-scale of
 analysis, but were significantly different between ranges: the RII
 followed a quadratic trend across the rainfall gradient in the western
 range, while this relationship was positive and close to linear at the
 eastern range. Then, by projecting the RII models (i.e., for abundance,
 cover, and richness) spatially through a consensus map, we show that most
 positive effects of V. caven are geographically found in dissimilar areas:
 the central part of Chile (western range) and across the Paraná river
 (eastern range). When local fine-scale predictors (i.e., annual herbs
 cover and height, and herbivores feces cover), were used to model each
 response variable at the plot level (underneath or outside V. caven)
 similar trends were kept as when considering only large-scale predictors.
 Synthesis: Here, we show that the effect of the same nurse species on
 neighbouring plant communities can be very different depending on ranges
 of distribution, stressing that its ecological function cannot be
 generalized and not only depends on local factors but also is large-scale
 context-dependent. 
description: # Large-scale facilitative effects of *Vachellia caven*
 ## Description of the data
 and file structure Three datasets are included. The first file (**RII
 Data.csv**) corresponds to the RII data, including the three RII variables
 (cover, richness, and abundance) and rainfall, for each contrast, site,
 and range. 1. RII variables are measured with the Relative Interaction
 Index (Armas et al., 2004)*, which varies between -1 and 1, with values
 &gt;0 expressing positive interactions, and values &lt;0 negative
 interactions. In this data, indicate the effect of comparing underneath
 versus outside V. caven conditions using each of the raw variables (cover,
 richness and abundance) 2. Range and site are categorical variables,
 indicating the side of the distribution range and the specific sampling
 location, respectively. 3. Contrast is a categorical variable, indicating
 the ID of the contrast sampled (underneath versus outside V. caven
 conditions). 4. Rainfall is measured in mm The second file (**Fine-scale
 data.csv**) corresponds to the fine-scale models data, where the variables
 are at the plot levels, plus several covariates, some of which were not
 used on the article. 1. Categorical Variables: Range; Site; Condition; and
 Contrast, have all the same structure as mentioned above. 2. Rainfall is
 measured in mm. 3. Studied fine-scale variables: Num_Spp = Species
 richness (n° of species); Num_Ind = Abudance (n° of individuals);
 Total_cover = total cover of plants growin withing the condition plot
 (from 0 to 100%). 4. Fine-scale covariates used in the study: Herb_cov =
 annual herbs cover (as %); Herb_height: annual herb height measured in m;
 Herbivory = herbivores faeces cover (as %) 5. Fine-scale covariates
 discarded during model construction: Ston_cov = Cover (%) of stones;
 Micr_slo = ground inclination (measured as angle); Crow_cov = Cover (%) of
 the crown projection (Vachellia caven in underneath condition, infrequent
 shrubs or trees in the outside condition) 6. Crow_area = Vachellia caven
 crown area (square meters) The third file (**Supplemental Data.xlsx**)
 summarizes the effect of Vachellia caven, by interacting taxa, by site and
 range. 1. Values in RII columns and Sites, are the Relative Interaction
 Index (Armas et al., 2004)* 2. Abbreviations in "Type": Neg =
 the species in general experience a negative interaction; Pos = the
 species in general experience a positive interaction; Neu = in general the
 species has a neutral interaction. *Armas, C., Ordiales, R., &
 Pugnaire, F. I. (2004). Measuring plant interactions: a new comparative
 index. *Ecology*, *85*(10), 2682-2686.