Hyper-dominant species drive unexpected functional shifts in North American birds
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Climate change has led to consistent intraspecific shifts in functional traits, yet the extent to which within-species trends predict community-level changes is unknown. We assessed how local community-weighted means of seven key traits have changed over the past 50 years across North American bird communities. Communities shifted toward larger body mass and smaller appendages over time, the opposite of widely documented within-species changes. These unexpected patterns arise from a small proportion (5%) of hyper-dominant species. Idiosyncratic changes in their abundances led to weak associations between functional shifts and climate but strong associations with human-induced land use changes. Our results reveal contrasting within-species responses to climate change and community-level responses to broader environmental dynamics, highlighting the importance of hyper-dominant species in shaping biodiversity under global change.
