Differential seed handling by two African primates affects seed fate and establishment of large-seeded trees

We examined the influence of seed handling by two semi-terrestrial African forest primates, chimpanzees (Pan troglodytes) and l’Hoest’s monkeys (Cercopithecus lhoesti), on the fate of large-seeded tree species in an afromontane forest. Chimpanzees and l’Hoest’s monkeys dispersed eleven seed species over one year, with quantity and quality of dispersal varying through time. Primates differed in their seed handling behaviors with chimpanzees defecating large seeds (>0.5 cm) significantly more than l’Hoest’s. Furthermore, they exhibited different oral-processing techniques with chimpanzees discarding wadges containing many seeds and l’Hoest’s monkeys spitting single seeds. A PCA examined the relationship between microhabitat characteristics and the site where primates deposited seeds. The first two components explained almost half of the observed variation. Microhabitat characteristics associated with sites where seeds were defecated had little overlap with those characteristics describing where spit seeds arrived, suggesting that seed handling in part determines the location where seeds are deposited. We monitored a total of 552 seed depositions through time, recording seed persistence, germination, and establishment. Defecations were deposited significantly farther from an adult conspecific than orally-discarded seeds where they experienced the greatest persistence but poorest establishment. In contrast, spit seeds were deposited closest to an adult conspecific but experienced the highest seed establishment rates. We used experimental plots to examine the relationship between seed handling, deposition site, and seed fate. We found a significant difference in seed handling and fate, with undispersed seeds in whole fruits experiencing the lowest establishment rates. Seed germination differed by habitat type with open forest experiencing the highest rates of germination. Our results highlight the relationship between primate seed handling and deposition site and seed fate, and may be helpful in developing models to predict seed shadows and recruitment patterns of large-seeded trees.

► Chimpanzees and l'Hoest's dispersed the seeds of one half of all large-seeded tree species.
► Microhabitat characteristics where a seed was deposited were in part explained by seed-handling, i.e. spit singly, wadged or defecated.
► Seed handling corresponded to different seed survivorship rates with orally-processed and discarded seeds experiencing the greatest establishment.
► Primates play a differentially significant role by dispersing large-seeded tree species into otherwise seed-limited areas.