Fig. 1.

Hypothesized relationships between species-specific traits, and ecological and anthropogenic factors and ground use by monkeys in the Americas and lemurs in Madagascar, and not any specific transition in one species or another. For species-specific traits, taxa exhibiting quadrupedal locomotion (inferred from their intermembral index (IMI)), have a larger group size, and have greater body mass are hypothesized to use the ground more. Taxa with diets consisting of more fruit, and exhibiting vertical clinging and leaping (VCL) and brachiator locomotion (inferred from their IMI) are hypothesized to spend less time on the ground. Regarding ecological factors, taxa inhabiting sites with higher maximum temperatures and greater primate species richness are hypothesized to use the ground more. Taxa inhabiting sites with a greater number of terrestrial predators and greater continuous canopy coverage are hypothesized to spend less time on the ground. Regarding anthropogenic factors, taxa inhabiting sites that are greater distances from roads are hypothesized to use the ground more, whereas taxa inhabiting sites that are closer to denser human populations are hypothesized to spend less time on the ground.