Terrestriality Across the Primate Order
Most primates live in the trees, but some have evolved to spend much of their time on the ground. To understand why, I compiled one of the largest global datasets on primate terrestriality and used advanced comparative models to test leading evolutionary hypotheses. The results reveal that ground use has evolved multiple times across the primate order, often in larger-bodied species and in more open, less structurally complex habitats. You can access this published work here, in the journal Evolutionary Anthropology.
To test hypotheses about primate terrestriality, I compiled data from published sources on 515 primate taxa into a single database. The map above shows the global distribution of primates in this dataset. Larger circles represent the most terrestrial species, which are concentrated in Africa and Asia, with few terrestrial species in the Americas.
I also visualized terrestriality across a phylogenetic tree to examine which primate lineages are most and least terrestrial. This tree highlights that terrestrial behavior is especially concentrated in the cercopithecines, particularly the papionins, which includes primates such as macaques, baboons, geladas, and mandrills.
I used a Bayesian hierarchical approach, accounting for primate phylogeny, to model three measures of terrestriality: binary (arboreal vs. terrestrial), ordinal (arboreal, semi-terrestrial, terrestrial), and continuous (percent of time spent on the ground). I also fit two additional models to examine how different factors influence terrestriality in catarrhines versus non-catarrhines. For all models, results are shown for both sex-averaged and female-only predictors.
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Below, explore the model outputs through coefficient plots, which illustrate the effects of various primate traits and ecological factors on terrestrial behavior.