Taxonomic, functional and phylogenetic beta diversity of upland forest birds in the Amazon: The relative importance of biogeographic regions, climate, and geographic distance

Aim: We address the relative importance of biogeographic regions (areas of endemism), regional climate, and spatial factors on taxonomic, functional, and phylogenetic β-diversity of bird assemblages in upland terra-firme forests in the Amazon.

Location: Amazon biome.

Taxon: Birds

Methods: We gathered 27,498 occurrence records of 873 bird species for 115 bird assemblages distributed in all nine biogeographic regions delimited by the major Amazonian rivers. Only data from studies surveying whole communities with standard sampling methods and exhaustive sampling effort were included. We partitioned the fractions of taxonomic, functional and phylogenetic beta diversity explained by climate, biogeographic regions, spatial factors, and the variation shared between them.

Results: Across the entire Amazon, we found higher total taxonomic (0.68±0.10) than phylogenetic (0.46±0.08) β-diversity, and low functional β-diversity (0.34±0.08). Biogeographic regions showed the highest unique contributions explaining taxonomic and phylogenetic β-total (7% and 5%, respectively) and turnover components (7% of β-jtu taxonomic, 7% of β-jtu phylogenetic), but accounted for only 2% of total functional β-diversity and trait turnover. Climatic variables explained slightly more trait nestedness (5%) compared to species and lineage turnover (3% each). Species composition was clearly distinct between biogeographical regions limited by the Amazon River, but support for the effect of other rivers was mixed.

Main conclusions: Our study highlights the significant influence of biogeographic regions and climate on species composition in the Amazon. However, our findings also suggest that the Amazon River exerts a more pronounced impact on species distribution compared to other major Amazonian rivers. Species turnover across biogeographical regions is particularly evident at the species level, with minor effects observed in functional traits, suggesting that taxonomic turnover is driven mainly by functionally redundant species. In addition, recent diversification events, predominantly occurring at the tips of the phylogeny without substantial turnover at deeper nodes, are likely responsible for the patchy distribution of species across Amazonia.

Methods
This work contains 27,498 occurrence records of 873 species, compiled for 115 bird assemblages distributed in the Amazon basin. Approximately 80% of the occurrence data were obtained from freely available literature, while ~20% were obtained from our fieldwork. The spreadsheet containing all occurrence data used in the analyses is provided. The trait data included here contain information on five traits for each species, obtained from the AVONET database (Tobias et al., 2022; https://onlinelibrary.wiley.com/doi/full/10.1111/ele.13898). For three of these traits—beak length, beak width, and tarsus length—we adjusted for differences in species body mass by dividing the trait values by the cube root of the respective species' body mass. We used the phylogeny proposed by Jetz et al. 2012 (BirdTree, http://www.birdtree.org) for phylogenetic analyses. For 55 recently split species not included in Jetz et al. (2012), we edited the tree by splitting the branch where the species originally was and placing new species according to the topology of the tree presented in the published literature for each complex of species that became separate species.