Where Seeds go when they go Far? Distance and Directionality of Avian Seed Dispersal in Heterogeneous Landscapes

Abstract

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 replicate 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 meters. We found that seeds arrive in greater densities and at longer distances in habitats with trees, particularly fleshy-fruited types, which produced habitat-specific seed dispersal kernels (2Dt probability density functions). Results also show a disproportional arrival of seeds in habitats similar to those of mother plants, which can have important demographic consequences for seed establishment, such as Janzen-Connell effects, but also help decrease the genetic similarity of intraspecific neighborhoods. Findings reveal the strong dependence of seed dispersal on the templates that guide the movements of animal dispersers in heterogeneous landscapes.