Genetic adaptation can play an important role in driving species distributions, yet genetic information is rarely integrated into models of species responses to climate change. Here, we present a new method to estimate required migrations speeds in response to climate change, while taking into account population-level genetic differentiation. We illustrate this method using balsam poplar (Populus balsamifera L.), a northern broad leaf tree species. Using generalized dissimilarity modeling to predict population-level genetic differentiation through time and space, we identified the location on the landscape in past climates that minimized genetic differentiation at climate-adaptive loci with respect to current population locations. By identifying these locations at different time periods during post-glacial expansion, we estimated the speed at which populations would need to have migrated to track climatic change through time while minimizing the amount of adaptive evolution required. We also projected our models to scenarios of future climate to estimate and compare predicted future and past migration speeds.
Results/Conclusions
We found that the estimated migration speeds of balsam poplar populations in response to future climate change may need to be more than ten times faster than those estimated since the last glacial maximum. The average estimated migration speed across balsam poplar’s range for past climate was approximately 71 m/yr, but was found to vary geographically. In general, northern portions of the range may have required faster migrations speeds than central or western portions of the range. Predicted future migration speeds far outpaced those estimated from past climates, often requiring speeds greater than 1000 m/yr for populations to keep pace with future climate change. In some parts of the range, predicted future migration speeds were found to be particularly high, sometimes approaching 20,000 m/yr. These finding suggest that, not only may the rate of future migration need to be considerably faster compared to past migration speeds, but that there is likely to be large variation in required migrations speeds across balsam poplar’s range. We emphasize that predicted migration speeds are based on climate-tracking of adaptive alleles, without incorporating effects of selection in situ, and hence may represent an upper estimate of migration speeds.