Consideration of dispersal processes and northern refugia can improve our understanding of past plant migration rates in North America

Abstract

Aim According to the palynological record, rapid plant migrations following the retreat of the last glacier were common in North America and Europe. However, providing an explanation for these rapid migration rates has been challenging considering modern-day seed dispersal distances. We used the newly developed seed dispersal functionality in a hybrid dynamic global vegetation model (DGVM) to simulate two theories that have been proposed to explain rapid plant migrations: long-distance seed dispersal and northern refugial populations.Location Idealized landscapes representing temperate and boreal regions of North America.Methods Vegetation migration rates for three species (Acer rubrum, Fagus grandifolia and Picea glauca) were simulated in response to climate change across a landscape. All simulations included long-distance seed dispersal; however, we compared landscape colonization rates both with and without the presence of northern refugial populations.Results For all three species, the colonization rates were faster when there was a northern refugial population. Increasing the number of locations of refugia further increased the rate of landscape colonization, and this was most effective when refugial populations were spatially separated. The perceived migration rates (i.e. the time it took to spread the furthest distance away from the southern refugium) were approximately twice as fast when a refugium was present. For example, A. rubrum had a perceived migration rate of 119 m yr À1 without refugia and a perceived migration rate of 204 m yr À1 with a northern refugium.Main conclusions The simulated migration rates that matched the rapid migration rates observed in the pollen record for Acer were only achieved when both long-distance dispersal and northern refugial populations were included in the simulations. Even with refugial populations, migration rates for P. glauca and F. grandifolia were slower than historical rates. The results of this study are consistent with the hypothesis that plant migration rates calculated from the pollen record overestimate the ability of most species to track rapid climate change.

Invoking adaptation to decipher the genetic legacy of past climate change

“…Hence, cryptic refugia appear to have played a major role during postglacial colonization, implying that the dispersal capacity of species is probably more limited than previously thought (Feurdean et al. , Snell and Cowling ).…”

“…A major inference from phylogeographic surveys over the past two decades is that small populations survived closer to the ice sheets during the last glaciation than previously suggested from fossil pollen data. These "microrefugial" outpost populations supplied colonists at the forefront of expansions during postglacial recolonization, which challenges the notion of rapid migration (McLachlan et al 2005, Anderson et al 2006, Feurdean et al 2013, Snell and Cowling 2015.…”

The critical role of local refugia in postglacial colonization of Chinese pine: joint inferences from DNA analyses, pollen records, and species distribution modeling

“…By contrast, recent phylogeographic surveys across the ranges of a number of species revealed genetic structures indicative of small refugial populations of trees that survived through the LGM in northern areas close to the ice sheets and sometimes even north of them (McLachlan et al 2005, Anderson et al 2006, Parducci et al 2012, Warren et al 2016. These findings highlight the importance of local spread from these refugia in postglacial forest development and allowed for more biologically realistic estimates of species migration rates for European and North American tree taxa (Feurdean et al 2013, Snell andCowling 2015).…”

Phylogeographic assessment of mtDNA paraphyly and the evolution of unisexuality inCalligrapha(Coleoptera: Chrysomelidae)

“…In every interglacial, these ice age survivors colonized newly available habitat after the retreating ice and the reestablishment of favorable conditions in previously glaciated areas relatively quickly, at least in the case of plants (Clark et al., ). These migrations took advantage of the physiographic configuration of North America, offering limited barriers to south–north dispersal (Soltis et al., ), but also to the mentioned fact that temperate species may have remained close to the newly available habitat as suggested by the analysis of dispersal rates and recent phylogeographic evidence in plants (e.g., Clark et al., ; Peterson & Graves, ; Rowe et al., ; Snell & Cowling, ). The cyclical range expansions throughout Ice Ages changed the distribution of species following a variety of, sometimes relatively congruent patterns (e.g., Soltis et al., ).…”