Résumé
SignificanceCombining genomic-based estimates of past effective population sizes for >260 extant species and comprehensive datasets of species-specific traits, we reconstruct patterns of avian functional diversity over the last million years and under pre-anthropogenic climate warming. Our results suggest an overall preservation of functional diversity over this time, but with a significant erosion of functional diversity across peripheral regions of functional space representing more extreme trait sets. Species most sensitive to climate warming occupied more redundant areas of trait space, but overall functional diversity declined significantly during this relatively short period of the Pleistocene. Our approach provides a major step forward in understanding temporal dynamics in functional diversity before humans began to exert broad-scale effects on the biosphere.
Despite evidence of declining biosphere integrity, we currently lack understanding of how the functional diversity associated with changes in abundance among ecological communities has varied over time and before widespread human disturbances. We combine morphological, ecological, and life-history trait data for >260 extant bird species with genomic-based estimates of changing effective population size (Ne) to quantify demographic-based shifts in avian functional diversity over the past million years and under pre-anthropogenic climate warming. We show that functional diversity was relatively stable over this period, but underwent significant changes in some key areas of trait space due to changing species abundances. Our results suggest that patterns of population decline over the Pleistocene have been concentrated in particular regions of trait space associated with extreme reproductive strategies and low dispersal ability, consistent with an overall erosion of functional diversity. Further, species most sensitive to climate warming occupied a relatively narrow region of functional space, indicating that the largest potential population increases and decreases under climate change will occur among species with relatively similar trait sets. Overall, our results identify fluctuations in functional space of extant species over evolutionary timescales and represent the demographic-based vulnerability of different regions of functional space among these taxa. The integration of paleodemographic dynamics with functional trait data enhances our ability to quantify losses of biosphere integrity before anthropogenic disturbances and attribute contemporary biodiversity loss to different drivers over time.