Does seed dispersal mode matter?

Zoochory is fundamental for habitat colonization by plants with large and heavy seeds, such as Araucaria angustifolia. Recruitment by this endangered South American conifer is heavily impacted by animals, but the effect of different zoochoric dispersal modes and deposition sites on successful establishment remains unknown. In this study, we evaluated the effect of dispersal mode (based on seed disperser), distance from adult conspecifics, and disposition site on long-term recruitment success. The experimental design included two environments (forest and open field), in each of which we established 30 microhabitat sampling stations simulating deposition sites (10 under a conspecific; 10 far from a conspecific and next to a landmark; and 10 far from a conspecific and without a landmark). Each microhabitat contained three levels of dispersal type (intact buried seed; intact seed on the ground surface; and partially predated seed on the ground surface), each with five seeds, totaling 900 seeds. In the forest environment, an experiment was also conducted to verify the fate of seeds using a spool-and-line technique. Neither environment nor microhabitat alone significantly affected seed survival, although dispersal type was significant in seed survival, as only buried seeds survived until the last survey. The spool-and-line seed experiment showed that most A. angustifolia seeds were predated after removal (81.5%) and only buried seeds survived, reinforcing the role of scatter-hoarding animals as important agents in A. angustifolia dispersal. Our results suggest that A. angustifolia seeds suffer high predation rates, with only a few seeds escaping from predators and recruiting seedlings into the population (only 1.1% of all seeds used in both experiments). We conclude that seed survival is a critical life cycle step in this plant species and that dispersal mode is critical for its reproductive success.