The speed of change in climate and land cover is associated with the speed of biodiversity changes in avian assemblages of the United States

PLOS One | https://doi.org/10.1371/journal.pone.0330153 August 29, 2025 6 / 20 number of LULC predictor variables, we performed the comparison using proportions (e.g., 1 of 3 climatic variables or 3 of 5 LULC variables were significant predictors). Results Effect of the rate of change of the environment on biodiversity across ecoregions On one hand biotic heterogenization and changes in richness of avian assemblages were linked to changes in climate and LULC. On the other hand, biotic homogenization and changes in the components of total assemblage dissimilarity were mostly linked to changes in LULC. Changes in biotic heterogenization were not driven by the same environmental factors from one ecoregion to another. Climatic changes were associated with changes in biotic heterogenization: rapid within-ecoregion heterogenization of avian assemblages was associated with both fast declines and increases in maximum temperature (Northern Forest; Table 1, Fig 2A), as well as with fast precipitation declines and rapid increase in minimum temperature (Northwestern Forested Mountains; Table 1, Fig 3A and 3B, 3D and 3E, respectively). Biotic heterogenization was also related to rapid changes in LULC. Northern Forests rapid assemblage heterogenization was related to fast forests declines (Table 1, Fig 2D). In the Northwestern Forested Mountains rapid assemblage heterogenization through species replacement was largely related to declines in forest faster than approximately −4.13x10-4 per unit time and increases in forest (though the

effect size was small, Fig 3M), as well as rapid increases in barren land (Table 1, Fig 3M and 3N for change in forest, and G for change in barren land). Bird assemblage homogenization was mainly associated with changes in LULC. In the Northern Forest, rapid homog- enization through lowered species loss was related to fast increases in grassland/shrubland and wetland (Fig 2G, and 2I, and 2M and 2O). Although grassland/shrubland and wetland are not large proportions of the overall forest LULC type, the observed changes were quite rapid. In the Northwestern Forested Mountains, rapid assemblage homogenization was linked to rapid declines in crop/pasture (Fig 3J and 3K). In this ecoregion, rapid homogenization through slowed species replacement was also associated with fast increase in precipitation (Fig 3A and 3B). Rapid homogenization was found at high elevations in the Eastern Temperate Forest (driven by slowed-down species replacement rates; Table 1, S2D Fig and S2E Fig in S1 File) and in the Great Plains (driven by slowed-down species losses; Table 1, S3D Fig and S3F Fig in S1 File). For the most part, changes in the components of total assemblage dissimilarity were related to changes in LULC. The single exception is that slowed species replacement coupled with fast species loss were associated with rapid increases in precipitation in the Eastern Temperate Forest (Table 1, S2B and S2C Fig in S1 File). Rapid species loss coupled with slower species replacement was also linked to rapid increases in wetland in the Great Plains (Table 1, S3B and S3C Fig

in S1 File). Conversely, rapid species replacement rates coupled with slower species loss were found at high elevations in the North American Deserts (Table 1, S4H and S4I Fig in S1 File). Rapid species replacement was associated with fast decreases in forest in bird assemblages (N = 13) located in areas with 30% or more of forest cover (averaged between 1990–2019) within the North American Deserts (S4E Fig, S8 Table in S1 File), while slower species replacement was related to fast increases in urban LULC in the Northern Forest (Fig 2K). Slowed species loss was linked to rapid increases in barren land in the North American Deserts (Table 1, S4C Fig in S1 File). At the local level, rapid increases in species richness were associated with rapid increases in maximum temperature (Eastern Temperate Forests; Table 2, S5A Fig in S1 File) and intermediate rates of precipitation declines (Northwestern Forested Mountains; Table 2, S5D Fig in S1 File). Rapid species richness increases were also related to fast increases in urban LULC (Northern Forests; Table 2, S5C Fig in S1 File) and to fast declines in crop/pasture, fast increases in forest, and rapid changes in grassland/shrubland in any direction (Northwestern Forested Mountains; Table 2, S5D-S5F, S5H Fig in S1 File). Rapid species richness declines were linked to rapid declines in forests (Northern Forests and Northwestern