Long-distance seed dispersal is a key ecological process responsible for population colonization, maintaining genetic diversity, and range shifts in response to the rapidly changing climate. Abiotic and biotic dispersal vectors facilitate seed movement, and vector behavior is frequently dictated by landscape heterogeneity. In this study, we examine gene flow across a complex, meso-scale landscape in two Pacific Northwest-native plant species with differing dispersal mechanisms. Plectritis congesta (Caprifoliaceae) seeds do not exhibit a strong dispersal syndrome and are primarily dispersed by gravity, and Achyrachaena mollis (Asteraceae) seeds produce a pappus for dispersal by wind. We isolated maternally inherited chloroplast DNA (cpDNA) from 26 P. congesta and 35 A. mollis populations across a distance of 30 kilometers in southern Oregon’s Rogue River Valley to estimate patterns of effective seed dispersal. Individual populations were pooled, and haplotypes frequencies determined using the CallHap bioinformatics pipeline. In addition to physical landscape features that may influence dispersal vectors, we also evaluated species habitat quality using ecological niche modelling. Using dispersal resistance tools, such as ResistanceGA and Circuitscape, we identified physical landscape and habitat quality features encouraging and inhibiting effective long-distance seed dispersal.
Results/Conclusions
Following bootstrap model selection, a combination of urban development, habitat quality, and rivers was the most significant predictor of Plectritis congesta cpDNA gene flow (marginal R2 = 0.542) with contributions of 57.2%, 20.6%, and 22.2% respectively. This model suggests effective seed dispersal of P. congesta is dependent upon occurrence of suitable habitat as well as a secondary dispersal mechanism; seeds may become lodged in the hooves of ungulates or other fauna as they migrate through P. congesta patches across natural areas. For Achyrachaena mollis¸ habitat quality has the greatest effect on gene flow (marginal R2 = 0.114; AICc = -255.6), followed by the elevation gradient (marginal R2 = 0.100; AICc = -253.7). As wind patterns are shaped by changes in topography, it follows the wind-dispersed syndrome of A. mollis influences seed dispersal across the landscape. The observed patterns of effective seed dispersal of both species emphasize the importance of considering suitable habitat as well as the influence of landscape features on vector behavior when evaluating the dispersal potential of plants.