Scale dependence of avian functional rarity reveals mismatches between global and local conservation priorities

This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint. You must log in to post a comment. There are no comments or no comments have been made public for this article. This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint. Add a Comment You must log in to post a comment. Comments There are no comments or no comments have been made public for this article. Aim. Spatial scale shapes both how rarity is defined and how conservation priorities are derived from it, yet most functional rarity assessments rely on a single (often global) reference pool. We test how the scale dependence of functional rarity affects hotspot identification and the alignment of global versus local conservation priorities in birds. Location. Global. Time period. Contemporary. Major taxa studied. Birds (10,906 species). Methods. Using AVONET morphological traits and global distributions, we quantified functional rarity as the average of two components: trait distinctiveness (mean distance to other species in trait space) and geographic restrictedness (1 − occupancy). We computed both components at four nested spatial scales (global, biogeographic realm, biome-within-realm, and local assemblage context). We then mapped assemblage-level functional rarity–weighted richness (Frwr) on a ~100 × 100 km grid, defined hotspots under two policy-relevant thresholds (top 7.1% and top 30% of cells), and quantified hotspot congruence among scales. Results. Trait distinctiveness was nearly invariant from global to biome scales, whereas restrictedness strongly decreased at finer scales, driving marked scale dependence in functional rarity. Hotspots identified using Frwr showed very low spatial overlap across scales (<4% shared), indicating that globally derived priorities often miss assemblages that are functionally rare in regional or local contexts. Multiscale hotspot convergence was concentrated in a limited set of regions, including major tropical mountain systems and island arcs. Main conclusions. Functional rarity offers a trait-based perspective on conservation value, but its interpretation depends on the reference pool and thus on scale. Integrating multiple scales is necessary to reconcile global biodiversity targets with the protection of regionally and locally distinctive ecological strategies. https://doi.org/10.32942/X2X37P Ecology and Evolutionary Biology functional rarity, scale dependence, conservation biogeography, birds, spatial prioritization, morphological diversity, functional distinctiveness, restrictedness Published: 2026-03-25 16:56 Last Updated: 2026-03-25 16:56 CC BY Attribution 4.0 International Data and Code Availability Statement: All code and derived datasets generated in this study—including species-level distinctiveness, restrictedness and functional rarity at four spatial grains; gridded functional-rarity-weighted richness (Frwr) layers; hotspot masks; and figure-reproduction scripts—are archived at Zenodo (DOI:https://doi.org/10.5281/zenodo.17513832). Input trait and range data are from the AVONET database (Tobias et al., 2022) and are openly available from the original repository https://figshare.com/s/b990722d72a26b5bfead. Realm/biome boundaries are from WWF Terrestrial Ecoregions, and protected-area polygons are from the World Database on Protected Areas (August 2023 release) and available via Protected Planet under standard terms of use. No new field data were collected. Language: English