Seed dispersal by western lowland gorillas: what about gut passage effect?

Animal-mediated seed dispersal is an essential ecological process in the tropics. Among African primates, the critically endangered western lowland gorilla (WLG) seems to fulfill many characteristics of an effective seed disperser. WLG preferentially disperses species of various seed-size into open canopy habitats suitable for seedling growth. However, few studies have addressed the effects of the passage through the digestive tract on germination. Thus, the effectiveness of WLG in ecological processes governing forest dynamics and regeneration is still poorly known.
Seed dispersal by WLG was studied in Central Gabon and Southeast Cameroon. Dispersed seed were identified from fresh fecal samples. Comparative germination trials based on 5 treatments (seeds from fresh fruits, seeds from fresh fruits surrounded by pulp, seeds from fresh fruits with fecal matrix, seeds from feces and seeds from feces with fecal matrix) were realized for 13 species. We recorded germination success for all species and germination delay for 6 species.
Our results suggest a neutral gut passage effect for 54% and positive effect for 40% of tested species. Germination success enhancement was linked to another factor than pulp suppression. For two species, pulp suppression enhanced germination success, but not gut passage. The presence of pulp or fecal matrix surrounding the seed seemed to longer germination delay, while gut passage would not fasten germination.
Globally, we conclude that WLG dispersed seeds are not damaged by gut passage. Consequently, WLG is thought to provide effective ecological services that could be essential to the maintenance and the recovery of forest ecosystems.