Environmental Variability Shapes Life History of the World's Birds

Theory suggests life history plays a key role in the ability of organisms to persist under fluctuating environmental conditions. However, the notion that environmental variability has shaped the distribution of life history traits across large spatial and taxonomic scales has gone largely untested using empirical data. Synthesising a collection of data resources on global climate, species traits, and species ranges, we quantified the role that environmental variability over time has played in shaping pace of life across the world's non-migratory, non-marine bird species (N = 7477). In support of existing theory, we found that species that experience high inter-annual temperature variability tended to have a slower pace of life, while the opposite was true for high intra-annual temperature variability. The effect of precipitation variability was less pronounced and more uncertain. These observed patterns were apparent despite the vastly different ecologies of our study species and evidence of strong phylogenetic constraint. Additionally, we highlight the importance of contextualising rates of environmental change in terms of the historical variability of environmental systems and species' pace of life. Species experiencing higher rates of relative environmental change, in terms of standard deviations per generation, may be most susceptible to climate change.