Diet disparity and diversity predict extinction risk in primates

Species vary in their vulnerability to extinction according to their biology, ecology, environmental factors and threats to which they are exposed. Diet is an important ecological trait that affects many aspects of a species' biology, including its vulnerability to extinction. Despite the importance of diet as a species' trait, its influence on extinction risk has only been studied in a coarse way, in part due to a lack of detailed diet data covering a large breadth of species or geographic areas. We examined the association between diet and extinction risk in primates, using a high-resolution dataset covering all major primate lineages and habitats on a global scale. The resolution of the dataset allowed us to calculate multiple biologically informative metrics for diet composition and diversity, allowing us to tease apart what aspects of diet were most important for predicting the risk of extinction, whilst accounting for phylogeny, body mass and geographic range size. Our results showed that both diet disparity and diet diversity predict primate extinction risk, showing that primates that are able to consume more types of items, and items that are more disparate from one another, are less prone to extinction. Furthermore, we found that although closely related species tend to have similar dietary diversity and disparity, these metrics vary widely amongst primate families. Primates with a high diet diversity and disparity may be able to cope better with fluctuations in food availability than species with homogeneous diet items, through a portfolio effect. Understanding the degree of dietary specialization of the species may help guide new studies relating to extinction risk and threats and be useful in future species assessments.