Community macroecological patterns and interspecific interactions in guild level regulate avian isotopic niche over time

Understanding how ecological patterns shift across space and time is key to comprehend how biological communities respond to environmental changes. We used stable isotopes to investigate the ecological mechanisms underlying community, trophic guild, and species-level organization in Atlantic Forest birds, focusing on the effects of long-term anthropogenic impacts. The study was based entirely on feather samples from bird specimens housed in Brazilian natural history collections, which proved fundamental to reconstructing temporal ecological baselines. We analysed carbon and nitrogen isotope ratios in 1778 specimens collected between 1893 and 2022 across two regions that share a history of human expansion: the Pernambuco and Serra do Mar areas of endemism. At the community level, all Layman metrics (niche area, δ13C and δ15N ranges, and trophic redundancy) increased over time, suggesting greater niche partitioning and potential specialization in modern communities. At the guild and species level, changes in niche metrics over time varied depending on the region of the Atlantic Forest. This finding reveals that anthropogenic changes can influence interspecific and intraguild interactions regionally. Our study underscores the critical role of bird collections in enabling large-scale ecological inference and demonstrates their unique value for understanding biodiversity responses in historically transformed tropical landscapes.