Plants and mammals once tracked climate closely, then mammal niches shifted under human pressure

Despite recent climate change, many plants and animals are not yet tracking climate as predicted. We reconstruct realized climatic niches for 16 plants and 45 mammals across North America from the end of the last deglaciation to the present, calculating climate fidelity to measure temporal niche stability. Plants consistently exhibit higher climate fidelity than mammals, despite limited dispersal. During the deglaciation, which had lower human impact, some large mammals tracked warming climates as effectively as plants. Following European colonization, mammalian niches shifted markedly. Large mammals were displaced from warm, humid regions toward colder, drier areas, while some small mammals expanded into human-modified landscapes. In contrast, plant niches remained largely structured by climate, highlighting stronger anthropogenic constraints on mammalian responses to climate change thus far.