Haurez B., Brostaux Y., Petre C.A., Doucet J.L.
In Central African tropical forests, the western lowland gorilla deposits most of the seeds it disperses in well-lit nesting sites that can favour seedling growth. The faecal matrix surrounding the seeds can act as a fertiliser and further enhance seedling development. This fertilisation effect had never been tested. Our research therefore aimed to determine whether seed deposition by gorillas (i) in faecal matter and (ii) in nest sites is advantageous for seedling development (growth rate and foliation rate) and survival (% of surviving seedlings). To assess the effect of the faecal matrix, seeds of Santiria trimera (Burseraceae), Chrysophyllum lacourtianum (Sapotaceae) and Plagiostyles africana (Euphorbiaceae) collected from gorilla faeces were sown in a nursery with and without a faecal matrix. Seedlings of Santiria trimera and Dacryodes normandii (Burseraceae) were established in nest sites and in closed canopy terra firme forest sites to assess the impact of seed deposition on seedling development and survival. The faecal matrix was observed to positively influence seedling development in the species studied, but showed no effect on survival. Regarding seed deposition sites, the development rates observed were two to ten times higher in the nest sites than in closed-canopy forest. This enhanced seedling development was positively correlated with canopy openness. In situ studies of seed germination, seedling growth and survival are needed to characterise the fate of gorilla-dispersed seeds more precisely. However, our results offer evidence that gorillas provide important directed dispersal services by depositing seeds most frequently in open canopy sites.
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