Effective dispersal patterns in prairie plant species across human-modified landscapes

Effective dispersal among plant populations is dependent on vector behavior, landscape features, and availability of adequate habitats. To capture landscape feature effects on dispersal, studies must be conducted at scales reflecting single-generation dispersal events (meso-scale). Many studies are conducted at large-scales where genetic differentiation is due to dispersal occurring over multiple generations, making it difficult to interpret the effects of specific landscape features on vector behavior. Genetic structure at the meso-scale may be determined by ecological and evolutionary processes, such as the consequences of vector behavior on patterns of gene flow. We used chloroplast haplotypes and nuclear genome SNP surveys to identify landscape features influencing seed and pollen dispersal at a meso-scale within the Rogue River Valley in southern Oregon. We evaluated biotic and abiotic vector behavior by contrasting two annual species with differing dispersal mechanisms; Achyrachaena mollis (Asteraceae) is a self-pollinating and anemochoric species, and Plectritis congesta (Caprifoliaceae) is biotically pollinated with barochoric seeds. Using landscape genetics methods, we identified features of the study region that conduct or restrict dispersal. We found chloroplast haplotypes were indicative of historic patterns of gene flow prior to human modification of landscapes. Seed dispersal of A. mollis was best supported by models of isolation-by-distance, while seed-driven gene flow of P. congesta was determined by the distribution of preserved natural spaces and quality habitat. Whole-genome genetic structure was driven by both pollen and seed dispersal, and both species responded to contemporary landscape changes, such as urban and agricultural conversion, and habitat availability.