An overlooked hotspot: persistence of large polyspecific assemblages of threatened primates in the unprotected Yabassi Key Biodiversity Area.

Abstract

The Gulf of Guinea rainforests, renowned for exceptional primate endemism, are increasingly fragmented and face severe hunting-induced defaunation. However, the long-term persistence of primate assemblages in these hunted forests remains understudied. The unprotected Ebo-Ndokbou-Makombe landscape, designated the Yabassi Key Biodiversity Area (YKBA), represents one of the region's largest remaining forest tracts, yet its primate community is largely unexplored. Research and conservation efforts within this landscape predominantly focus on the Ebo block to protect its cryptic gorilla population, while Ndokbou and Makombe receive less attention. Here, we assess the persistence and polyspecific assemblages of diurnal primates across the three forest blocks. From January to December 2019, we surveyed over 1,500 km of reconnaissance walks and sighted seven IUCN Threatened and one Near-Threatened species, including chimpanzees Pan troglodytes ellioti (56 groups and 296 nest groups), putty-nosed monkeys Cercopithecus nictitans (435 groups), crowned monkeys C. pogonias (251), red-eared monkeys C. erythrotis (122), mona monkeys C. mona (108), Preuss's monkeys Allochrocebus preussi (97), red-capped mangabeys Cercocebus torquatus (40), and drills Mandrillus leucophaeus (20). Notably, over 40% of primate encounters were polyspecific groups with up to five species. Despite conservation focus on Ebo, encounter rates, association patterns, and group sizes were comparable across Ebo, Ndokbou, and Makombe. Interestingly, primate encounter rates and assemblages in this unprotected landscape were also similar to observations in Korup National Park located within the same ecoregion. These findings underscore the critical conservation value of the YKBA and call for urgent landscape-scale interventions to mitigate hunting pressure and maintain habitat integrity.