Abstract
Aim Species distributions are altered by climate change, resulting in changes in community composition. How communities are changing with climate is important for understanding the dynamics of changing diversity patterns. In this study, we employ two community weighted means (CWMs) of temperature (CTI) and precipitation (CPI) to evaluate patterns in climate‐driven community changes. Location Eastern North America between −100° and −60° longitude and 25°–50°N latitude. Taxon North American birds Methods We used North American Breeding Bird Survey (BBS) data from 1990 to 2018 to test the spatiotemporal trends of these indices at a sub‐continental (across all BBS routes) and at a regional scale (sub‐continental scale partitioned by 5° latitude bands). We employ a jackknife analysis to highlight individual species contributions to CTI and CPI trends and further identify group characteristics of species based on relative abundance trends and range expansion and contraction trends. Results Across all BBS routes, temperature marginally increased and precipitation significantly increased. At the sub‐continental scale, we found no correlation between CTI and temperature, but a positive correlation between CPI and precipitation. CTI and CPI both increased, driven by increased abundances of “warm” and “wet” dwelling species expanding in range. Regional scale CTI and CPI patterns deviated from sub‐continental patterns. CTI was driven by “warm” dwelling species increasing in abundance and expanding in range, whereas decreases in “dry” dwelling species contracting in range drove CPI trends at the highest latitudes. Main conclusions The concurrent use of CTI and CPI highlights that community dynamics are more complicated than using temperature metrics alone. Employing more than one community index demonstrates how simultaneous increases in two separate evaluative indices can have disproportionate effects on the number of species that contribute to a trend and highlight disparate mechanisms that contribute to these underlying differences.