DOI: 10.6084/m9.figshare.30404353.v1
title: Exploring scale-dependent differences in Elton's biotic resistance hypothesis <i>vs.</i> Darwin's naturalization hypothesis in subtropical nature reserves

description: <b>Aim: </b>Elton's biotic resistance hypothesis (BRH) suggests that higher resident diversity confers resistance to invasion, and Darwin's naturalization hypothesis (DNH) posited that a greater phylogenetic distance between the invader and resident species promotes invasion success. However, the results of Elton's and Darwin's hypotheses vary depending on the spatial scale, testing the applicability of the two classical hypotheses in different scales would help to understand the successful invasion of alien plants. We aimed to determine (i) whether both Elton's and Darwin's hypotheses demonstrate similar results at plot, transect, and reserve scales; (ii) how climate change and human activities affect these two classical hypotheses at different spatial scales.<b>Location</b><b>: </b>Thirteen national nature reserves, Guangxi, China.<b>Major taxa studied: </b>Herbaceous plants.<b>Methods: </b>We constructed a phylogenetic tree of 467 herbs including native and invasive herbaceous species based on a field survey of 246 transects and 1,046 plots in 13 national nature reserves in Guangxi. Then we calculated the phylogenetic diversity of native herbs (PD) and the mean phylogenetic distance between native and invaders (MPD). Relative abundance, cover, and richness of invasive alien herbs were treated as response variables, and we used generalized linear mixed effects models to test the spatial scale dependencies of these two classical hypotheses, as well as the variations in prediction trends under different levels of human interference and climate scenarios.<b>Results: </b>Based on relative abundance, cover, and richness metrics, our findings support both BRH and DNH at plot and transect scales, but not at the reserve scale. Invasive herbaceous species were more likely to naturalize into phylogenetically distant native communities near human settlements (high disturbance intensity), consistent with DNH. In addition, BRH showed steeper prediction slopes under warmer climatic conditions, indicating enhanced native community resistance. However, extreme temperatures reversed the positive relationship between phylogenetic distance and naturalization probability observed at plot and transect scales, thus weakening support for DNH. Precipitation significantly influenced prediction outcomes, though without consistent spatial scaling patterns. Furthermore, invasive herbaceous species exhibited elevation-dependent adaptive strategies: pre-adaptation dominates in warmer low-elevation zones, while naturalization processes prevail in cooler high-elevation areas.<b>Main conclusions: </b>Our study evaluated the roles of observation scales, climatic factors, and anthropogenic disturbance in biological invasions across Guangxi's nature reserves. Invasive alien herbaceous primarily confirmed DNH, while native phylogenetic diversity demonstrated resistance against invasion. Both patterns showed weak spatial scale dependence. Warmer climates enhanced native community resistance, whereas human interference facilitated invasive colonization. This study provides empirical evidence for understanding invasion mechanisms along environmental gradients and offers scale-sensitive insights for managing plant invasions in subtropical protected areas.