Does the seed disperser matter? The influence of dispersal type on survival of Araucaria angustifolia seeds

Zoochoric dispersion is fundamental for the colonization of habitats by plants with large and heavy seeds such as the Paraná pine (Araucaria angustifolia). This is an endangered conifer from South America whose recruitment is heavily impacted by animals, but the way that different zoochoric dispersal modes and deposition sites can affect its successful establishment is not known yet. Thus, in this study, we aimed to evaluate the effect of dispersal mode (accordingly to the seed disperser), distance from adult conspecifics, and disposition site on long-term recruitment success. The experimental design included two environments (forest and open field) and each of them received 30 micro-habitat sampling stations (simulating deposition sites: 10 under conspecific; 10 far from conspecifics, next to a landmark; and 10 far from conspecifics, without a landmark), and each microhabitat had three levels of dispersal type simulating animal treatment (intact buried seed; intact seed over the ground; partially preyed seed over the ground), each with five seeds, totaling 900 seeds. In the forest environment, an experiment was also conducted to verify the fate of seeds using the spool and line technique. The environment and the micro-habitat alone did not explain seed survival, although the dispersal type given by the animal disperser was significant for survival and the buried seeds were the only ones that survived until the last survey. With the spool and line seed experiment, we attested that most of the Paraná pine seeds were preyed after removal (81.5%), and only buried seeds survived, reinforcing the role of scatter-hoarding animals as important agents in the Paraná pine dispersal. This way, our results showed that Paraná pine seeds suffer a very high predation rate, and that only a few seeds escape from predators and recruiting (only 1.1% of the all seeds used in the two experiments), indicating that the survival of seeds is a critical step in the life cycle of this plant, highlighting the role of dispersal mode in recruiting success.