Adaptive responses of animals to climate\ud change are most likely insufficient

Biological responses to climate change have been widely documented across taxa and regions,but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. We reviewed 10,090 abstracts and extracted 71 studies from 58 relevant publications, to assess quantitatively whether phenotypic trait changes associated with climate change are adaptive in animals. A meta-analysis focused on birds, the taxon best represented in our dataset, suggests that global warming has not systematically affected morphological traits, but has advanced phenological traits. We demonstrate that these advances are adaptive for some species, but imperfect as evidenced by the observed consistent selection for earlier timing. According to a theoretical model, the evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species.