Abstract
Wild primates face a wide range of anthropogenic influences globally that impact their health, fitness, and survival. One area of potential impact that has been particularly understudied is the supplementation of wild primate diets with human foods. Although the consumption of human foods represents a substantial dietary change for wild primates, knowledge of how it impacts their physiology and behavior is limited. Here we explore how human food supplementation impacts wild primates by comparing the gut microbiomes of free-ranging brown howler monkeys (Alouatta guariba) in periurban Brazil that do or do not have access to human foods. We found that howler monkeys consuming human foods had reduced gut microbial diversity and reduced relative abundances of fiber degrading microbial taxa, which has been associated with negative health consequences in other animals, including humans. However, the effect size of these differences was relatively small and varied over time. Additionally, the composition of the gut microbiome varied significantly across months, regardless of the access to human foods. We suggest that the biology of this howler monkey population is minimally impacted by human foods. Further empirical research will help clarify the relationship between human food supplementation and health across primate populations, facilitating conservation applications.