Woody plant taxonomic, functional, and phylogenetic diversity decrease along elevational gradients in Andean tropical montane forests: environmental filtering and arrival of temperate taxa

Abstract

AimMountains are paramount for exploring biodiversity patterns and their causes due to the rich mosaic of topographies and climates encompassed over short geographical distances. Biodiversity changes along elevational gradients have traditionally been explored in terms of taxonomic diversity, but other aspects must be considered. For first time, we simultaneously assessed elevational trends in the taxonomic, functional, and phylogenetic diversity of woody plants in Andean tropical montane forests (TMFs) and explored their underlying ecological and evolutionary causing processes. LocationTropical Andes Time period2011/2012 and 2017/2019 Tropical Andes Major TaxaWoody plants MethodsWe investigated taxonomic, functional, and phylogenetic diversity along four transects (traversing ca. 2,200 m altitudinal gradients) encompassing 114 0.1 ha plots across a broad latitudinal range (ca. 10{degrees}). We used Hill numbers to quantify differences in the abundance-based diversity of 37,869 woody plant individuals with DBH [≥] 2.5 cm. ResultsTaxonomic, functional, and phylogenetic diversity decreased as elevation increased. The decrease was less pronounced for Hill numbers of higher orders. The only exception was a slight increase in phylogenetic diversity when more weight was given to dominant species. These results were consistent between transects. Main conclusionsThe decrease in taxonomic and functional diversity with elevation might be due to an environmental filtering process where the increasingly harsher conditions towards highlands exclude species and functional strategies. Besides, the differences in the steepness of the decrease between Hill orders suggest that rare species contribute disproportionately to functional diversity. The shifting elevational trend in the phylogenetic diversity between Hill orders indicates a greater than previously considered influence in central tropical Andean highlands of species originated in lowlands with strong niche conservatism relative to distantly related temperate lineages. This could be explained by a decreasing presence and abundance of extratropical taxa towards the central Andes relative to northern or southern Andes. BIOSKETCHGuillermo Banares-de-Dios is a plant ecologist with interests in community assembly, biodiversity patterns, and global change. He completed his PhD in 2020 and belongs to "Grupo de Ecologia Tropical", an international network of researchers from different institutions with broad interests in tropical biology (http://www.grupoecologiatropical.com/?lang=en). Currently he works as Project Manager implementing the European Pollinator Monitoring Scheme in Spain.