Phylogenetic assembly of angiosperms through space and time in Europe and North America in the Holocene

ABSTRACT Background Phylogeny-based assessments of Holocene vegetation are rare. They are important for understanding eco-evolutionary dynamics of species assembly under environmental changes and ever-increasing anthropogenic pressure. Aims To reveal any spatio-temporal variation in the phylogenetic dispersion (PD, mean phylogenetic distance of co-occurring taxa) in angiosperm pollen assemblages in mainland Europe and North America and their relationship with regional climate and anthropogenic influence. Methods Using 12,250 and 14,898 fossil pollen assemblages from Europe and North America, respectively, we analysed family level spatio-temporal variation in Holocene PD by hierarchical generalised linear models and tested its concordance with Holocene climate and anthropogenic influence by Procrustes randomisation tests. Results Holocene PD exhibited a reverse-humped pattern along latitudinal gradients in both continents. A longitudinal pattern in Holocene PD in Europe was not pronounced. However, in North America, it declined irregularly along the gradient from west to east. PD in both continents varied significantly during the early- and late-Holocene in concordance with Holocene climate and anthropogenic influences. Complex fine-scale spatio-temporal variations in PD were also pronounced. Conclusion Profound and complex Holocene eco-evolutionary changes in angiosperm assemblages in Europe and North America correspond largely to changes in extrinsic and intrinsic drivers and mechanisms of ecological changes. Future environmental changes of similar or a greater magnitude may drive further changes in the phylogenetic structure of the assemblages. A more detailed study of their eco-evolutionary dynamics requires detailed spatio-temporal assemblage data with precise taxonomy and census, and a detailed and robust species-level phylogeny of the species pool. Key policy highlights Phylogenetic dispersion (PD) in angiosperm pollen assemblages varied significantly in space and time in Europe and North America during the Holocene (past 12,000 years). Spatio-temporal variation in Holocene PD is mostly concordant with the dynamics of Holocene climate and anthropogenic influence on both continents. Future environmental changes of similar or a greater magnitude than in the Holocene may drive significant changes in phylogenetic structure (eco-evolutionary assembly of taxa) of the assemblages.