Community assembly on inland cliffs is context‐dependent

Abstract

Under harsh environmental conditions, community assembly processes are expected to drive pronounced functional convergence, with communities dominated by stress‐tolerant species. Integrating local communities with their regional species pools enables evaluating environmental filtering and disentangling habitat‐specific assembly processes. To assess whether the strength and direction of environmental filtering in extreme habitats depends on regional climate and topography, we adopted a trait‐based approach on a relatively underexplored habitat such as inland limestone cliffs. To test whether limestone inland cliffs function as extreme habitats that filter regional species pools towards stress‐tolerant trait syndromes or alternative habitat‐specific assembly processes, we sampled vegetation on inland limestone cliffs along an aridity gradient in three study areas spanning different European biogeographic regions, namely Alpine, Continental and Mediterranean. We compiled regional species pools from the Global Biodiversity Information Facility and integrated them into trait‐based null models to compare observed community structure against expectations under stochastic assembly, using a combination of functional traits compiled from field measurements and from databases. Additionally, to assess whether community assembly rules are shared across regions or shaped by regional context and topography, we quantify trait‐based non‐random assembly and functional convergence across biogeographic regions and different cliff aspects. The results show that in inland limestone cliffs, extremeness is context‐dependent. It varies with the selected traits, intensifies in humid regions and weakens on pole‐facing slopes in dry regions. Cliff plants showed reduced plant height across all regions and aspects, whereas leaf dry matter content was higher and seed mass was lower under specific conditions. These patterns indicate non‐random trait distributions towards conservative leaf strategies and reduced plant size, while the prevalence of small propagules may facilitate colonization of suitable microsites for establishment, often scarce and spatially scattered. Functional convergence occurred in the Alpine region and on equator‐facing cliffs in the Mediterranean region, with slope and microtopographic heterogeneity showing limited effects. Overall, inland limestone cliffs showed evidence of non‐random trait assembly and localized abiotic filtering, suggesting that these patterns are context‐dependent. Read the free Plain Language Summary for this article on the Journal blog.