Large-scale facilitative effects of Vachellia caven
Data files
Dec 08, 2023 version files 109.26 KB
Abstract
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.
README: Large-scale facilitative effects of Vachellia caven
https://doi.org/10.5061/dryad.j0zpc86n5
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.
- RII variables are measured with the Relative Interaction Index (Armas et al., 2004)*, which varies between -1 and 1, with values >0 expressing positive interactions, and values <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)
- Range and site are categorical variables, indicating the side of the distribution range and the specific sampling location, respectively.
- Contrast is a categorical variable, indicating the ID of the contrast sampled (underneath versus outside V. caven conditions).
- 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.
- Categorical Variables: Range; Site; Condition; and Contrast, have all the same structure as mentioned above.
- Rainfall is measured in mm.
- 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%).
- 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 %)
- 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)
- 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.
- Values in RII columns and Sites, are the Relative Interaction Index (Armas et al., 2004)*
- 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.