PHYLOGENETIC AND ENVIRONMENTAL CONTROLS ON THE GEOGRAPHIC RANGE DYNAMICS OF WOODY PLANTS SINCE THE LAST GLACIAL MAXIMUM

The size and location of a taxon’s geographic range is dynamic - contracting, expanding, or shifting in location over time in response to changes in suitable environmental and ecological conditions. Despite this lability, some previous comparisons across lineages have found that range sizes are conserved, or more similar among closely-related than distantly-related taxa. Such similarities are unexpected under an allopatric model of speciation which predicts asymmetric range sizes between sister taxa at least early in their histories. However, conservatism in life history traits may counteract such asymmetry, particularly if closely-related taxa share dispersal traits which make them either “rapid expanders” or “slow movers”. Here we assess whether geographic range is conserved by focusing on the phylogenetic structure of geographic range shifts among woody plants in eastern North America following the Last Glacial Maximum using a molecular phylogeny and geographic data from the pollen fossil record. We find that the velocities with which woody plant genera shifted their range limits between 16-10 ka were positively correlated over time - i.e., lineages that moved further in one interval also tended to move further in subsequent intervals – with the strength of this correlation weakening towards the present-day (< 10 ka) as climatic velocities slowed. We assessed the phylogenetic signal in the mean and variance of biotic velocities over the Quaternary using a Brownian motion model of trait evolution and find that neither was correlated with phylogeny. Furthermore, we show that the present-day range sizes of woody plant genera in eastern North America are also independent of phylogeny, thereby reducing the likelihood that the phylogenetic independence we observe reflects simply the decoupling of range dynamics occurring over relatively short (~2 ka) versus long (>16 ka) intervals of time. Lastly, we assess the phylogenetic structure of life history traits and their correlation with biotic velocities.