DOI: 10.5061/dryad.2r5k78d
title: Data from: The shape is more important than we ever thought: plant to plant interactions in a high mountain community

description: 1. Plant to plant interactions are probably the most important driver of
 species coexistence at fine spatial scales, but their detection represents
 a challenge in Ecology. Spatial point pattern analysis (SPPA) is likely
 the approach most used to identify them however, it suffers from some
 limitations related to the over-simplification of individuals to points.
 2. Here, we propose a new approach called Overlapping Area Analysis (OAA)
 to test whether the consideration of the shape and orientation of the
 individuals reveal signs of interactions between species that would remain
 undetected with SPPA. We used this approach to analyze a fully-mapped
 cryophilic grassland in Sierra de Guadarrama National Park (Spain), where
 the crown of each individual plant (i.e. the canopy) was approximated by a
 polygon. We then computed and compared the total overlapping area between
 the canopy of a focal species and that of any other species in the
 community with the expectations of a null model of random rotation of each
 plant around its centroid. We complemented the results of our new approach
 by comparing with that of SPPA of plants’ centroids. 3. Results of OAA
 showed that up to 41% of species pairs had less canopy overlap than
 expected, suggesting that many interspecific canopy associations in this
 plant community were significantly negative at the finest spatial scale.
 Contrarily, SPPA estimated that 12% of species pairs were positively
 associated at spatial scales up to 20 cm, confirming the facilitative
 effect displayed by the main engineer in the community (Festuca curvifolia
 Lag.) and by some other dominant species. 4. Our new approach quantifying
 canopy associations provides new insights into the processes guiding
 community assembly. Whereas the results of SPPA suggested the prevalence
 of traditional “stress gradient hypothesis” (i.e. prevalence of positive
 interactions under stressful abiotic conditions), OAA revealed that many
 interspecific canopy associations were significantly negative. Overall,
 most facilitated species optimized this positive effect by placing their
 centroids as close to the benefactor species as their foraging behaviour
 allowed while avoiding crown overlap. The method proposed is available in
 a dedicated R-package that will facilitate its application by other
 ecologists.
description: OAA test
 scriptThis file includes an R
 script to compute the Overlapping Area test using the data of a
 fully-mapped cryophilic grassland in Sierra de Guadarrama National Park
 (Spain), where the crown of each individual plant (i.e. their canopy) for
 a total of 11 species was approximated by a polygon. The summary statistic
 employed in the test (i.e. result5) is the overall sum of the overlapping
 areas of intersecting polygons between each species pair. The observed
 overlapping area (i.e., the real overlapping area) is the first value in
 the vector, and the subsequent ones (i.e. 9999) are the overlapping areas
 of randomly simulated spatial configurationsOAA
 test.ROA observed and
 simulated valuesThis file includes a
 large array (result5) for using in R, that represents the summary
 statistic employed in the OAA test. This array is the overall sum of the
 overlapping areas of intersecting polygons between each species pair. The
 observed overlapping area (i.e., the real overlapping area) is the first
 value in the vector, and the subsequent ones (i.e. 9999) are the
 overlapping areas of randomly simulated spatial
 configurationsOverlapptest
 tutorialThis file includes an R
 script tutorial that explains how to conduct an overlapping area analysis,
 as in Pescador et al. (in press) “The shape is more important than we ever
 thought: plant to plant interactions in a high mountain community”, using
 the overlapptest package.