Where do seeds go when they go far? Distance and directionality of avian seed dispersal in heterogeneous landscapes.

Seed dispersal at large scales strongly influences plant population dynamics. Still, ecologists have rarely measured seed dispersal at relevant scales, and the role of habitat types in affecting seed dispersal at long distances remains unexplored. We studied seed dispersal of Ilex aquifolium and Crataegus monogyna in northern Spain, hypothesizing that seeds would be recovered at higher rates and at longer distances (LDD) at habitats with fleshy-fruited trees, compared to habitats with other tree types or at open habitats. We tracked seeds in eight landscapes by enriching trees with 15N isotopes at the center of landscapes, and then detected 15N-marked seeds by sampling at distances of up to 700 m. We found that seeds arrive in greater densities and at longer distances in habitats with trees, particularly fleshy-fruited types, producing different LDD probabilities for each habitat. Results also show a disproportional arrival of seeds in habitats similar to those of mother plants, which should affect seed establishment and the genetic diversity of plant neighborhoods. Findings reveal the strong dependence of seed dispersal on the existing templates that guide the movements of avian dispersers in heterogeneous landscapes and also suggest that LDD above tree lines and beyond hard habitat edges can be difficult.