Global impacts of anthropogenic threats on bird and mammal diet functional groups

Anthropogenic threats vary in how they affect individual species, functional diversity, and consequently, ecosystems as a whole. However, which groups of species are most affected by specific threats remains poorly understood. To evaluate which bird and mammal functional groups are most affected by specific threats, we use data aggregated by the International Union for Conservation of Nature (IUCN) to calculate the extent to which diet functional groups and body size explain the global impacts of the most common anthropogenic threats. For both birds and mammals, we found that terrestrial vertivores, aquatic predators, and frugivores (including mammalian nectivores and granivores) are most negatively impacted by anthropogenic threats, with crops and livestock as the top threats to vertivores, climate change and pollution for aquatic predators, and logging for the frugivores. Threats associated with plantations and recreation/work affect less than 5% of species across functional groups. Body mass is positively correlated with the impact of anthropogenic threats especially for hunting, such that larger species are substantially more threatened by hunting than smaller species. Our results reveal that bird and mammal vulnerabilities vary by diet functional group, body mass, and the type of anthropogenic threat. Given our findings that functionally important groups (i.e., predators and frugivores) are disproportionately impacted by multiple anthropogenic threats, and that individual threats differ in their severity across functional groups, we recommend targeting conservation actions to mitigate threats in a manner that will preserve critical ecosystem functions.