Genetic divergence in population mean fitness is weakly associated with environmental and geographic distance in four prairie perennial forbs

Plant propagules are frequently relocated between populations for restoration, especially in fragmented ecosystems like prairies, where few pristine patches remain. While research shows that plant populations often perform better in their native environments than in foreign sites, this pattern is not universal. The extent to which plant population fitness varies with distance from its site of origin remains unclear. Using aster models, we investigated the relationship of fitness with geographic distance and climate differences between the source and experimental sites for four perennial prairie forbs by planting 12 populations of each species at a north and south experimental site in the tallgrass prairie of Minnesota, USA. At both experimental sites, individuals from warmer and southern source sites had greater fitness, but the deviations of population mean fitnesses from the fitted relationships were substantial and idiosyncratic. Our results suggest limited effectiveness of geographic distance and temperature difference in predicting population mean fitness. This challenges the efficacy of long distance seed transfers as seed sourcing strategies to promote population persistence in prairie restorations.