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 3 / 20 different rates and directions of changes in multiple environmental predictors can also differ across ecoregions at a con- tinental scale. Our study is one of the first to perform a long-term context-dependent analysis of the relationship between the rate of change of biodiversity and the rate of change in the environment with a comparison across ecoregions of the United States. We can test hypotheses about rates of change in LULC or climate in different ecoregions against rates of change in biodiversity, where biodiversity is defined as species richness or assemblage dissimilarity. Although species richness has received much more research attention, it is important to assess how environmental changes affect biodiversity at differ- ent scales of ecological analysis (e.g., comparing environmental effects on species richness and assemblage dissimilar- ity). Particularly, the components of assemblage dissimilarity, species replacement and species loss or gain [43], could all be important. Including the components of assemblage dissimilarity in the analysis allows for a more nuanced interpreta- tion of the processes behind the biodiversity patterns observed. Human-induced changes in climatic conditions and the loss or degradation of habitats that accompanies the con- version of natural LULC to human-modified ones, directly impact the suitability of an area for the species typically found there. Changes in habitat suitability can determine the presence (or absence) of individual species in particular

locations through different mechanisms. For example, unmet species-specific physiological and/or ecological require- ments can result in phenological mismatches [44,45] and/or altered species interactions [44,46] that can ultimately affect a species geographical distribution. When the responses of multiple individual species to changes in habitat suitability are analyzed together across time and space, the impact of these changes on the diversity of avian assem- blages emerges. In this study, we combined spatial and temporal approaches to assess the effect of rates of change in climate and LULC on the rate of change of species richness and assemblage dissimilarity in five ecoregions during a thirty-year period in the United States. Specifically, we hypothesized the following: 1) The rate of change in environmental variables (by which we mean climate, LULC, or both) will be associated with rates of change in all levels of biodiversity, and their com- ponents. As to which environmental driver is more strongly associated with changes in different biodiversity levels, based on the limited literature available, we hypothesize that 2) the relative importance of climate change and LULC change will be dependent on the ecoregion. Methods Data Biodiversity rate of change data. We used the rates of change in the species richness and assemblage dissimilarity of North American breeding birds across 30 years (1990–2019) obtained by [42]. We obtained data from the North American Breeding Bird Survey (BBS, [47]. We selected BBS routes in the conterminous United States sampled once a

year in the period 1990–2019 that were sampled for more than 24 years, eliminating those that were not sampled in two or more consecutive years. Then, we retained only one BBS route per 10 × 10 km map grid cell by randomly eliminating one of two sampling units closer than 15 km (‘spThin’ R package, [48]. As in [42], this analysis included a total of 571 BBS routes: 309 on the Eastern Temperate Forest, 95 on the Great Plains, 61 on the Northern Forests, 56 on the Northwestern Forested Mountains, and 50 on the North American Deserts. Fig 1 in [42] illustrates the geographic distribution of the 571 BBS routes included in the study. We used the same exclusion and retention criteria as in [42] including in the analysis a total of 245 bird species (Table S1 in [42]). We converted the species abundances reported in the BBS to presence- absence data. We calculated the rates of change of species richness, total assemblage dissimilarity and its components as in [42]. Climatic data. The climatic data were obtained from the Parameter-elevation Regressions on Independent Slopes Model (PRISM) datasets for the years 1990–2019 (PRISM Climate Group 2014; [49]. For this study, we