Chimpanzees as ecosystem service providers: Seed dispersal of an economically important plant resource at Fongoli, Senegal
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Vertebrate-mediated seed dispersal is a vital mutualistic interaction in tropical ecosystems that is beginning to be recognized for its role in sustaining populations of plant resources on which people rely for food, medicine and other materials. Some studies have demonstrated that avian seed dispersers provide such ecosystem services whereas other taxa, such as primates, have received little attention in this regard despite their known importance as seed dispersers. Frugivorous primates are currently presumed to sustain forest resources utilized by people, but this hypothesis remains untested. To test this, I examined the effectiveness of critically endangered western chimpanzees (Pan troglodytes verus) as seed dispersers of an economically important fruit resource, Saba senegalensis, at the savanna-woodland site of Fongoli, Senegal. I hypothesized that these apes provide an effective seed dispersal service to Saba, likely sustaining its populations. Germination experiments were conducted on gut-passed seeds alongside seeds removed from fruits and observations were made on the germination and seedling establishment success of chimpanzee-dispersed seeds in situ. Experiments showed that gut passage decreased the delay to germination while increasing the likelihood of its occurrence when compared to unprocessed seeds that were removed from fruits. Chimpanzee-dispersed seeds germinated and established when left in situ and were distributed non-randomly across the landscape. Chimpanzees biased seed dispersal to gallery forest habitats, which had a positive effect on Saba germination and establishment and they dispersed seeds less often than expected to grassland habitats, which had a negative effect on germination and establishment. Chimpanzees therefore promote early stages of Saba recruitment by providing an effective gut treatment and depositing seeds to sites that allowed for germination and establishment to occur. They therefore likely play an important role in sustaining Saba populations at Fongoli. These results provide evidence that critically endangered primates can provide important ecosystem services via seed dispersal. Conservation and natural resource management policy throughout the tropics should emphasize the link between primate frugivores and the forest products that humans depend on.