Seed dispersal by monk sakis (Pithecia monachus)

Seed dispersal by animals traditionally considered seed predators challenges the classical dichotomy between antagonistic and mutualistic plant-animal interactions. Pitheciines are typically regarded as specialized seed predators due to their seed-masticating feeding behavior, yet evidence suggests they can also contribute to endozoochorous seed dispersal when seeds escape damage during ingestion. We investigated fecal samples of monk sakis (Pithecia monachus) in a seasonally flooded forest in western Amazonia over the course of one year, quantifying and identifying intact seeds recovered from the samples. Of 92 fecal samples analyzed, 54% contained one or more intact seeds, with up to 17 seeds and three morphospecies per sample. In total, we recovered 165 intact seeds representing 20 morphospecies, all small-seeded taxa with a maximum seed length of < 1 cm. Fresh fecal pellets float on the water surface in flooded forest habitats, suggesting a potential interaction between endozoochorous and hydrochorous dispersal. Although we did not assess seed viability or germination, our results demonstrate that monk sakis can contribute to seed dispersal through gut passage and place them along the seed dispersal-predation continuum. These findings highlight the need to further investigate the dispersal potential and ecological significance of seed-predating primates.