Mycophagy in Primates of the Issa Valley, Tanzania

Mycophagy (fungi consumption) is an important animal-ecosystem interaction and provides nutrients for numerous mammalian taxa, such as primates. Although mushroom consumption is a widespread behavior documented in about a quarter of all known primate species, surprisingly little is known about their use of mushrooms as either a staple or fallback food and the relationship between mushroom availability and consumption. We used direct observational data on mushroom consumption in the diet of three sympatric primate species: chimpanzees (Pan troglodytes schweinfurthii) and red-tailed monkeys (Cercopithecus ascanius) from 2019 to 2022, and yellow baboons (Papio cynocephalus) from 2015 to 2022 in a mosaic woodland habitat in the Issa valley, western Tanzania, to address these gaps. We analyzed mushroom consumption patterns and assessed mushroom availability from line transects for a period of 15 months (Oct 2022-Dec 2023). Our findings show that mushrooms were a consistent dietary component for all three species during the wet season (October-April; chimpanzees-4%, baboons-17% and red-tailed monkeys-4%), while baboons also continued to consume mushrooms (~11% of their annual diet) even when availability was low outside the wet season. This is also the first report of mushroom consumption by red-tailed monkeys. We conclude that mushrooms serve as a fallback resource for Issa chimpanzees and red-tailed monkeys, while they represent a preferred food for Issa baboons. We contextualize mushroom consumption as a potential strategy of niche partitioning to reduce interspecific feeding competition and underscore the importance of mycophagy and its role in primate dietary ecology and human evolution.