Community Dynamics of Browsing and Grazing Ungulates

The world’s 240 ungulate species belong largely to the same guild, feeding on terrestrial plants, and yet, ungulates typically occur in multi-species assemblages. What allows multiple ungulate species dependent on similar resources to coexist? We focus on the role of variation in ungulate body masses and their feeding adaptations in facilitating coexistence at multiple scales. Our analyses of a global dataset of extant ungulates (incl. proboscideans) show that grazing species tend to have significantly larger body masses, browsers significantly smaller, and mixed feeders tend to have body masses similar to the global median of all species. We report evidence for body mass structuring in grazer and browser assemblages at the biome scale, presumably brought about by the interplay of competitive and facilitative interactions. Our analyses of the Pleistocene species assemblage indicate biased extinction of species across body mass extremes, and point to the role of Pleistocene extinctions in determining the continental ungulate assemblages of today. Our findings also indicate the possibility of mass extinctions not just of larger bodied species but of smaller bodied ungulates as well; this may have gone undetected so far, or is most likely, poorly represented in the fossil record.