Climate Effects on Mammalian Body Size and Grassland Composition Inferred from Late Quaternary Grazers in the Great Plains of North America

Authors

• Tom Baldvins, University of Nebraska-LincolnFollow

Date of this Version

Spring 3-31-2015

Document Type

Thesis

Citation

Baldvins, T., 2015, Climate effects on mammalian body size and grassland composition inferred from late Quaternary grazers in the Great Plains of North America [M.S. thesis]:Lincoln, University of Nebraska, 66 p.

Comments

A thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Earth and Atmospheric Sciences, Under the Supervision of Professor Ross Secord. Lincoln, Nebraska: February 2015.

Copyright (c) 2015 Tom D. Baldvins

Abstract

Several mammalian taxa exhibited a diminution during the Pleistocene-Holocene transition. Two hypotheses have been proposed to explain this phenomenon: (1) human hunting and (2) climate change along with its effects on grasslands. I use stable isotopes from a variety of Quaternary grazing mammals to measure grassland changes following the Last Glacial Maximum (LGM) in Nebraska and to develop a climate proxy to compare with mammalian body size. Results indicate that latest Pleistocene equids and mammoths have δ¹³C values indicative of a C₃ or mixed C₃/C₄ diet. However, Holocene bison have greatly elevated δ¹³C values, indicating a diet dominated by C₄ vegetation, suggesting a northerly expansion of C₄ grasses with the warm conditions following the LGM. High δ¹³C values from Bison bison sampled in this study suggest a greater abundance of C₄ grasses in Nebraska than today, and may indicate that these bison lived during the Holocene thermal maximum. Bison bison sampled in this study display a significant but weak correlation (r²=0.20, p=0.004, n=39) between δ¹³C and first molar occlusal area, which acts as a proxy for body size, indicating that size decreased as dietary C₄ increased and climate warmed; however, weakness of the correlation does not support previous hypotheses that attribute bison diminution solely to increased dietary C₄. These data indicate that other factors, such as temperature, aridity, and/or human hunting, are needed to explain the decrease in bison body size. On the other hand, a strong significant relationship (r²=0.83, p=0.011, n=6) between δ¹³C and equid metacarpal length of middle Pleistocene equids spanning both warm and cold intervals suggests that an increase in body size occurred with warming. I propose that both of these trends in body size were driven by changes in productivity. C₄ dominated habitats of the Holocene provided less primary productivity than mixed C₃/C₄ habitats contributing to bison diminution, while increased productivity during warmer intervals of the Pleistocene allowed equids to increase in size.

Advisor: Ross Secord