Journal of Biogeography. 2020;00:1–17. wileyonlinelibrary.com/journal/jbi | 1 © 2020 John Wiley & Sons Ltd Received: 15 April 2020 | Revised: 27 August 2020 | Accepted: 3 September 2020 DOI: 10.1111/jbi.13986 RESEARCH PAPER Historical legacies and contemporary processes shape beta diversity in Neotropical montane streams Juan David González-Trujillo 1,2,3 | Victor S. Saito 4 | Danielle K. Petsch 5 | Isabel Muñoz 6 | Sergi Sabater 2,3 1 Universidad Nacional de Colombia - Sede Bogotá, Bogotá, Colombia 2 Catalan Institute for Water Research (ICRA), Girona, Spain 3 Institut d’Ecologia Aquàtica, Universitat de Girona, Girona, España 4 Departamento de Ciências Ambientais, Universidade Federal de São Carlos, Rodovia Washington Luis, São Carlos, Brazil 5 Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais, Universidade Estadual de Maringá, Maringá, Brazil 6 Department of Evolutionary Biology, Ecology and Environmental Sciences, Universitat de Barcelona. Av. Diagonal, Barcelona, Spain Correspondence Juan David González-Trujillo, Universidad Nacional de Colombia - Sede Bogotá, Carrera 45 # 30-02, Bogotá, Colombia 111321. Email: jdgonzalezt@gmail.com; jdgonzalezt@ unal.edu.co Funding information Departamento Administrativo de Ciencia, Tecnología e Innovación; Generalitat de Catalunya; European Social Fund, Grant/ Award Number: 2019 FI_B1 00210; CRSIB, Grant/Award Number: 1706925B9AA Handling Editor: Simone Fattorini Abstract Aim: Contemporary dispersal constraints and environmental conditions are broadly recognized as significant drivers of beta diversity patterns. However, beta diversity patterns may also reflect the legacy of past climatic and geological events. In this study, we investigated the relative importance of historical and contemporary factors as drivers of taxonomic, functional and phylogenetic beta diversity in Neotropical stream communities. Location: The Colombian Orinoco basin. Taxon: Diatoms and insects. Methods: We estimated taxonomic, phylogenetic and functional beta diversity using Baselga's (BAS) and Podani's (POD) frameworks. Following both frameworks, we fur- ther partitioned every biodiversity facet into turnover and nestedness or richness difference components. Then, we used generalized linear models (GLM) to relate each biodiversity facet with environmental, spatial and historical factors. Results: We found that both historical and contemporary factors affected current patterns of beta diversity. Historical factors and water pH and temperature had the strongest effect on beta diversity patterns, particularly for taxonomic and phyloge- netic facets. GLM models performed better for insects than for diatoms in all three facets. Within communities, our analysis also revealed a partial congruence between BAS- and POD-based results. Main conclusions: Due to their past geological history and contemporary environ- mental gradients, tropical montane streams are natural laboratories for disentangling the joint effects of ecological and biogeographical factors on biodiversity patterns. Our study reveals that present-day distribution patterns cannot be fully explained without accounting for the effects of past geological and climatic events on mountain landscapes. In the Neotropics, montane geology sets the stage for speciation and landscape formation, with which ecological (e.g., dispersal limitation) and environ- mental factors interact to generate spatial variation in species turnover. KEYWORDS aquatic insects, benthic diatoms, community assembly, ecoregion, historical legacy, metacommunity, Sørensen