Seed predation of Araucaria angustifolia (Araucariaceae) in the Brazilian Araucaria Forest: influence of deposition site and comparative role of small and ‘large’ mammals

Abstract

Seed predation and seed dispersal are key factors that determine plant recruitment. In this study, we compared the role of small (<200 g) and ‘large’ mammals as predators of Araucaria angustifolia (Araucariaceae) seeds in the Brazilian Araucaria Forest. We also investigated the effect of deposition site, namely open grassland, forest edge or forest interior (>50 m from the edge) on seed-removal rates. We conducted field experiments on seed removal in July 2003 and 2004. We compared the habitat types using two exclusion treatments: semi-permeable exclosure (exclusive access of small rodents) and an open control (access of all mammal groups). We considered proportion of seeds removed after 15 days to investigate the effect of year, habitat type, and exclusion treatment on seed removal by using three-factor permutational ANOVA. We also evaluated seed fate and seed consumers by using spool-and-line devices attached to seeds and camera trapping. The results showed that seed removal differed significantly between years and among habitat types, but not between exclusion treatments. Removal rates were higher in 2004 than in 2003 and also were significantly lower in the open field when compared with both forested types (edge or interior) in both years. There was also a significant interaction between ‘year’ and ‘habitat’ which was driven by an increase in 2004 removal rates in the open field compared to the previous year. Our combination of manipulative experiments, camera-trapping survey, and spool-and-line seed tracking demonstrated that small rodents are responsible for the majority of seed removal of A. angustifolia in the study area. The low removal rates in open habitats indicate that they could serve as safe sites for A. angustifolia seeds. The results also suggested a potential role of small rodents as seed dispersers (about 4% of removed seeds were not consumed). The knowledge of how fragmentation affects pattern of seed predation and establishment of A. angustifolia through changes in abundance of different-sized mammals is essential for the conservation of the Brazilian Araucaria Forest and its most characteristic species.