Congratulations to Bian Wang, who successfully defended her dissertation on Thursday, May 13, 2021
Advisor: Catherine Badgley
The order Artiodactyla is a diverse group of terrestrial mammals that have been important components of terrestrial ecosystems since the Eocene. Understanding artiodactyl dietary ecology in relation to environmental gradients, morphological traits, and isotope ecology provides useful tools for making ecological inferences in the fossil record. I analyzed these topics in a wide range of extant species with a six-category classification of herbivorous diets, including frugivores, browsers, browser-grazer intermediates, generalists, variable grazers, and obligate grazers
First, I analyzed the ecological diversity represented in the diet and body size of extant artiodactyls in relation to climate and topography. Higher species richness is generally associated with greater ecological diversity, and the high artiodactyl richness in Africa is achieved by accommodation of more ecological traits as well as more coexisting species with the same traits. A range of ecological diversity levels, however, can occur in different areas with comparable species richness. Tropical and subtropical Asia supports a high dietary diversity comparable to that of Africa, despite having considerably fewer species, implying a more even distribution of species among ecological categories. Seasonal extremes of temperature and rainfall are important climatic predictors of artiodactyl richness. The dietary extremes (frugivores and obligate grazers) occur in the most restricted climatic conditions. The occurrence of these dietary categories in the ungulate fossil record, as well as the ecological structure of fossil ungulate faunas, can be useful for inferring paleoclimatic conditions
Next, I conducted ecomorphological analyses of bovid mandibles with landmark-based geometric-morphometrics. Mandibular morphology proves to be useful for differentiating dietary categories. Frugivores differ from browsers and obligate grazers from variable grazers. Notably, frugivorous bovids have a distinct mandibular shape that is readily distinguished from all other dietary groups. The main differences in mandibular shape among dietary groups are related to the functional needs of species during forage prehension and mastication. Compared to browsers, both frugivores and grazers have mandibles that are adapted for higher biomechanical demand of chewing. Additionally, frugivore mandibles are adapted for selective cropping. These results offer an approach for reconstructing the diet of extinct bovids with mandibular morphology.
Third, I compiled a global dataset of carbon-isotope composition of tooth enamel to evaluate the isotopic composition of ingested forage (δ13Cdiet). The herbivore dietary spectrum is expressed through increasing mean δ13Cdiet values from frugivores to obligate grazers, although the most depleted values occur in browsers that live under dense forest canopy. In general, grazing taxa have a wider range of δ13Cdiet values than browsing taxa. Notably, variable grazers exhibit a bimodal distribution of δ13Cdiet values, with North American taxa consuming C3 vegetation and African taxa consuming C4 vegetation, reflecting the different amounts of C4 biomass available in these regions today. Variation in δ13Cdiet values also occurs among ecoregions, taxonomic groups, and geographic regions. Grassland ecoregions differ significantly in δ13Cdiet values from forest ecoregions. Some of the oldest ruminant lineages have maintained C3 feeding, and pure C4 dietary signals are dominant in two bovid clades. Clarifying the contributing factors to variation in δ13Cdiet will refine paleoecological reconstructions. Overall, findings from these analyses support use of the more detailed dietary classification in the study of fossil artiodactyls. Identifying frugivory and obligate grazing, especially, will inform paleoenvironmental reconstructions.