Repeated trends in altitudinal gradients of diversity: How habitat filtering and biotic interactions structure ecological communities.

Understanding how biodiversity is structured along tropical elevational gradients requires disentangling the relative roles of regional evolutionary history and local processes shaping ecological assemblies. Here, Ithomiini butterfly communities were studied along repeated elevational gradients in two Neotropical regions with contrasting evolutionary histories: the Amazonian Andes and the Guiana Shield. The study tested whether similar elevational patterns of taxonomic, mimetic and phylogenetic structure emerge despite distinct regional species pools, and whether abiotic and biotic factors contribute to shaping these patterns. Despite marked regional differences in overall richness, consistent elevational patterns emerged across both regions. Taxonomic and mimetic richness increased with elevation and were accompanied by stronger phylogenetic clustering, indicating that similar habitat filtering processes operate along altitudinal gradients irrespective of regional context. Phylogenetic β-diversity was predominantly driven by lineage turnover, particularly in the Andes, highlighting the role of elevational gradients in promoting replacement of phylogenetically distinct lineages rather than simple species loss. These shared patterns suggest that altitude has a strong and repeatable effect on community structure, with habitat filtering acting locally on regionally distinct species pools. Abiotic factors such as temperature appeared to constrain species distributions at broad spatial scales, whereas biotic interactions acted more locally. In particular, butterfly diversity was positively associated with potential host plant richness and predation pressure, indicating that ecological interactions can further shape local community composition once broad-scale environmental constraints are accounted for. By integrating phylogenetic structure, biotic interactions and environmental gradients across regions with contrasting evolutionary histories, this study shows how regional species pools and local ecological filtering jointly shape tropical biodiversity and highlights that similar elevational assembly processes could arise independently across the Neotropics.