Data and R Code for Testing the Stress–Dominance Hypothesis in Aquatic Macrophyte Communities Using Hierarchical Generalized Additive Models

This repository provides the dataset and R code used to investigate the Stress–Dominance Hypothesis (SDH) in aquatic macrophyte communities using hierarchical generalized additive models (HGAMs). The analysis examines relationships between three response variables (Range, T4, and T2) and two ecological gradients representing competitive adversity and environmental adversity. The dataset comprises 1,812 observations classified by waterbody type, allowing the assessment of both overall ecological responses and waterbody-type-specific variation. Six alternative generalized additive model structures are considered: a null model (null), a global smooth model (G), a global smooth with group-specific deviations (GS), a global smooth with group-specific smooths (GI), a factor-smooth interaction model (S), and a model with group-specific smooths without a global component (I). Models are compared using the corrected Akaike Information Criterion (AICc), with smoothing parameters estimated by maximum likelihood (ML). Model performance is evaluated using adjusted R², deviance explained, effective degrees of freedom (edf), and approximate significance tests for smooth terms. The R code also generates graphical representations of fitted relationships and their 95% confidence intervals. Repository contents env.txt — Input dataset containing response variables, ecological adversity gradients, and waterbody classifications. HGAM_SDH_English.R — R script for model fitting, AICc-based model comparison, statistical summaries, and visualization. HGAM_SDH_English.docx — Documented version of the R analysis code. Reproducibility The analyses are implemented in R using the mgcv package for generalized additive modelling, together with packages for data manipulation and graphical visualization. To reproduce the analyses, users should update the input file path in the R script to match their local directory structure. The repository is intended to support transparency, reproducibility, and further investigation of context-dependent ecological responses to competitive and environmental adversity in aquatic macrophyte communities.