Fine-scale habitat heterogeneity and vole runways influence seed dispersal in Plagiobothrys nothofulvus

Seed dispersal allows plants to colonize new sites and contributes to gene flow among populations. Despite its fundamental importance to ecological and evolutionary processes, our understanding of seed dispersal is limited due to the difficulty of directly observing dispersal events. This is particularly true for the majority of plant species that are considered to have gravity as their primary dispersal mechanism. The potential for long-distance movement of gravity-dispersed seeds by secondary dispersal vectors is rarely evaluated.

We employ whole-genome assays of maternally inherited cpDNA in Plagiobothrys nothofulvus to resolve patterns of genetic variation due to effective (realized) seed dispersal within a 16 hectare prairie that is characterized by a mosaic of habitat types. We evaluate the effects of microgeographic landscape features extracted from micro-UAV aerial surveys on patterns of seed dispersal using landscape genetics methods.

We found evidence of high resistance to seed-mediated gene flow (effective dispersal) within patches of Plagiobothrys nothofulvus, and strong genetic structure over distances of less than 20 m. Geographic distance was a poor predictor of dispersal distance, while landscape features had stronger influences on patterns of dispersal (distance and direction of seed movement). Patterns of dispersal were best predicted by the combined distribution of flower patches, habitat type, and the network of vole runways, with the latter explaining the largest proportion of variation in the model.

Our results suggest that primary dispersal occurs mostly within microhabitats and infrequent secondary dispersal may occur over longer distances due to the activity of small mammals and other vertebrates.