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 15 / 20 Interactions between the rates of change in climate and LULC. Changes in climate and LULC can interact in their effects on biodiversity [25,26,93]. In this study, it was not possible to explore the effects of interactions among these two types of predictors due to data quantity limitations for some ecore- gions. This restricts our findings to the additive effects of the rate of change in climate and LULC on the rate of change of biodiversity. Nevertheless, our results suggest that the effects of the rate of change in climate and LULC combined produce compositional changes in the bird assemblages in different directions. Rapid within-ecoregion heterogenization of species assemblages was driven by high rates of temperature change and rapid declines in precipitation, plus rapid declines in forests and grassland/shrubland. Homogenization within an ecoregion was faster in species assemblages experiencing rapid increases in precipitation, grassland/shrubland, and wetland or rapid declines in crop/pasture LULC. Consistent with our findings, previous studies have found that warming or drying climates combined with habitat loss or an increase in land use intensity severely affect species assemblages and population trends of insects and birds [25,26,93]. Relative importance of climate and LULC as drivers of rate of change of biodiversity In general, the rates of change in LULC were stronger predictors of bird assemblage rearrangement than rates of change

in climate. In all ecoregions, there were significant relationships between at least one LULC variable and the rate of change of assemblage dissimilarity. The effects of the rate of change in climate, however, were only significant for the rate of change of species richness and assemblage dissimilarity in three of the five ecoregions. Other authors have found differential effects of climate and LULC on avian population trends as well [19,82]. In particular, the rate of change in LULC was a more important predictor of the rate of change of biodiversity in ecoregions dominated by low elevations (i.e., Great Plains and North American Deserts) and high latitudes (i.e., North- ern Forest). Climate was more important for the rate of change of biodiversity in the Eastern Temperate Forest. Only in the mountainous region of the Northwestern Forested Mountains did the rate of change in both climate and LULC show similar importance in predicting biodiversity change. These results support the idea that the rate of change of climate and LULC affects species assemblages differentially by ecoregion [18,19]. A previous study in northern Europe reported that forest bird assemblages were more impacted by climate change [19], similar to our findings for the Eastern Temper- ate Forest. This same study found that farmland birds were impacted by changes in both climate and LULC [19], which contrasts with our findings for the Great Plains. This discrepancy in results may be linked to differences in species compo-

sition of the bird assemblages and the rate of change of the environment in different regions of the world. In any case, our results highlight the importance of considering multiple environmental factors and ecoregion-specific analysis in com- munity ecology since threats to species assemblages can arise from changes in climate or LULC independently, or their combined effect [15], and vary per region [18,19]. Conclusions Changes in climate and/or LULC are driving the processes of community assembly and breakdown more than just driving the pattern of species richness and these assemblies and breakdowns can occur near one another within the same ecoregion. The more obvious changes are occurring in high altitude and high latitude ecoregions. For some ecoregions, components of total assemblage dissimilarity are responding to the environment in opposite ways. For all ecoregions, LULC was a stronger predictor of change in biodiversity metrics than was climate. Assemblage dissimi- larity was better predicted (by the environment) than was species richness, despite the fact that species richness is the better studied phenomenon. It is only through examining trends in multiple biodiversity indices, meant to capture multiple levels of action (species richness versus assemblage dissimilarity) that we would be able to observe the complex and changing interrelationships between biodiversity (species richness and assemblage dissimilarity) and the environment (climate and LULC).