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 12 / 20 2. Species replacement and species loss showed association with environmental factors in opposite directions. 3. The rates of change in LULC were stronger predictors of rates of change in biodiversity than the rates of change in climate. 4. The rate of change in total assemblage dissimilarity was better predicted by the rate of change in the environment than was the rate of change of species richness. Effect of the rate of change of the environment on biodiversity across ecoregions Increase of within-ecoregion assemblage dissimilarity (biotic heterogenization). High latitude and high elevation places showed strongest relationships between biodiversity metrics and environmental drivers. Rapid within-ecoregion heterogenization of avian assemblages was associated with fast changes in climate and LULC in ecoregions at high latitudes or elevations such as the Northern Forest and the Northwestern Forested Moun- tains. These results point to the susceptibility of species assemblages at higher latitudes and elevations to environmental change also documented for other taxa [2,4,24,38,60,61]. Species at the edges of their thermal or habitat tolerances – due to species-specific physiological limits and breadth of ecological niches – will be particularly vulnerable to the changes we documented here. For the two ecoregions with strongest relationships between the rates of change in biodiversity metrics and the envi-

ronment, there were different environmental drivers and different outcomes (i.e., more species loss versus more species replacement). Below, we explore these two ecoregions further. The rate of within-ecoregion heterogenization of avian assemblages was impacted differentially by environmental variables in the Northern Forest and the Northwestern For- ested Mountains. In general, the biological mechanism through which the biodiversity of bird assemblages was chang- ing in response to environmental changes was also different between the two ecoregions, with species assemblages becoming subsets of richer assemblages in the Northern Forest and species being replaced in the Northwestern Forested Mountains. Changes in temperature were associated with increased heterogenization in avian assemblages in these two ecore- gions. Rapid changes in maximum temperature (Northern Forest) and minimum temperature (Northwestern Forested Mountains) were associated with rapid heterogenization of avian assemblages. Warming temperatures may have resulted in rapid increase in abundance and range areas of warm-dwelling species while cool-dwelling species decreased [62,63]. The heterogenizing effect of warming temperatures has been reported under current [24] and future [64] climate warm- ing, in line with our results. These results likely indicate that some species were tracking climate change more rapidly or accurately than other species, as others have found [65,66]. The rate of biotic heterogenization may, however, not be

high enough to keep the pace of the warming climate [67], since the stronger the climate warming, the more species’ responses may lag behind at range limits [68]. In the Northwestern Forested Mountains (but not the Northern Forest), increased water stress (i.e., declining precipita- tion) was associated with increased biotic heterogenization of avian assemblages. In the Northwestern Forested Moun- tains, rapid biotic heterogenization was also associated with rapidly drying locations. Increased water stress has been associated with range shifts to higher elevations, particularly when combined with changes in temperature [69]. Thus, species intolerant to low precipitation levels going rapidly locally extinct and species tolerant to low precipitation levels replacing them appear to be the mechanism behind the fast heterogenization of montane species assemblages undergo- ing decreases in precipitation. Decreases in precipitation have also been linked to population declines in European birds in mountainous regions due to phenological mismatches between resource availability and breeding season [70]. Rapid forest losses were generally associated with an accelerated rate of biotic heterogenization in the Northern For- ests and the Northwestern Forested Mountains. However, the mechanisms behind this pattern were potentially different