Mandrills are the world largest monkeys and live in large social groups in Central African rainforest. Fragmentation of their forest habitat by logging roads creates smaller, isolated groups with higher predation risk and reduced genetic diversity.
Mandrill groups in fragmented forests cannot maintain the large horde sizes that provide protection from leopard predation. Smaller isolated groups have reduced genetic diversity over generations. Logging roads that penetrate forests create hunting access, directly causing mortality of group members. The social disruption from the loss of experienced adults affects group foraging efficiency and predator vigilance for the remaining members.