Rocking the landscape: Chacma baboons (Papio ursinus) as zoogeomorphic agents

Animals sculpt landforms by physically altering the substrate. Many digging and burrowing animals are then considered zoogeomorphic agents. While the significance of soil disturbing species is well established, geomorphic impacts are rarely quantified for rock transporting species. The chacma baboon (Papio ursinus), a widespread and abundant primate throughout most of southern Africa south of the Zambezi, may be a zoogeomorphic agent through its role in rock displacement while foraging. We quantified baboon rock movement along belt-transects placed across a catena in a semi-arid Karoo environment in South Africa. Along each transect, we the counted the number of moved rocks and recorded their dimensions, mass and shape and related this to rock (i.e., mass, shape) and landscape (i.e., hillslope, obstacles that hinder movement) features to assess the drivers of the extent of rock transport. Baboon rock movement was found to be extensive, ranging from 26 to 54,615 kg (10,967.2 ± 2300.9 kg) of rock material displaced per ha and year. The distance of rock movement was influenced by rock size (large rocks were displaced further) and rock shape (flat rocks were moved further, followed by angular and rounded rocks). Furthermore, slope influenced rock movement, with rocks displaced greater distances on steeper slopes. Baboon rock movement brought about a loss in potential energy and a change in landscape entropy through the net downward movement of rocks. We show that baboons play an important geomorphic role and probably serve as a keystone species as they are the only species in this environment to intentionally move rocks in this way. Because baboons are considered pests and are widely persecuted, their role in zoogeomorphic processes are vulnerable to being lost.