Dispersion of large-seeded tree species by two forest primates: primate seed handling, microhabitat variability, and post-dispersal seed fate

I describe the relative effectiveness of two primates in dispersing large-seeded tree seeds (> 0.5 cm) in the Nyungwe National Park (NNP), Rwanda. My objectives are three-fold: (1) to describe the relative effectiveness of primates in dispersing the seeds of five large-seeded tree species, (2) to evaluate the influence of primate seed-handling method on seed fate, and (3) to determine the influence of deposition site on seed fate. I employed focal tree observations, day-follows of habituated primate groups, in situ monitoring of primate-dispersed seeds, and experimental plots to achieve these objectives. Data were collected over the course of one year (April 2006 – April 2007). Frugivore assemblages dispersed the seeds of four of the five focal tree species. Chimpanzees and cercopithecines spent the most time in trees and had the largest group size. Large-bodied birds (LB) and chimpanzees dispersed the highest number of seeds per minute. LB and cercopithecines potentially disperse the greatest number of seeds for Ekebergia capensis, and chimpanzees for Syzygium guineense. My study highlights the complexities of determining a disperser’s effectiveness and suggests that large-bodied birds and primates are relatively important dispersers of large-seeded trees. Primates deposit seeds most often in open forest where seeds experience the highest establishment. In addition primates deposit seeds in five habitats that are likely dispersal-limited suggesting that primates contribute to the regeneration processes of otherwise dispersal-limited areas. My results suggest that the former emphasis of seed dispersal studies on defecations is not representative and should be expanded to include orally-discarded seeds. Furthermore my study highlights that primates do not deposit seeds randomly and that the characteristics of the deposition site are a reflection of primate seed handling. I found no relationship between the top five fruiting tree species found in chimpanzee feces and fruit availability suggesting that chimpanzees do not choose fruits solely based on their availability. In contrast the wadged fruits of Syzygium guineense are positively correlated to fruit availability. A closer examination of the relationship between chimpanzees and S. guineense may provide insight into potential repercussions on the regeneration of S. guineense if the chimpanzee were to be extirpated. I compare the relationship of seed presence in the NNP chimpanzees’ feces and wadges and forest-wide fruit availability with two other chimpanzee communities in the Albertine Rift. Finally I organized a workshop for educators living in communities on the NNP’s periphery in an effort to disseminate my results to a broader community. Pre- and post-workshop questionnaires completed by workshop participants suggest that this kind of interaction between researchers, management authorities and local peoples helps to build trust as well as identify areas where sensitization of the population may be needed.