Ehleringer, J.*; Cerling, T.: Possible relationships between atmospheric carbon dioxide and mammalian grazers

We explore the possible relationships between photosynthetic pathway, changing atmospheric carbon dioxide, and mammalian herbivores. Atmospheric carbon dioxide levels have changed over the last 200 million years; the recent pattern of increasing anthropogenic emissions has resulted in a dramatic increase in atmospheric carbon dioxide today that differs from atmospheric carbon dioxide in the glacial-interglacial cycles of the past. At the same time, many questions remain unanswered about abrupt changes in mammalian diversity. Might the observed changes in atmospheric carbon dioxide and changes in mammalian diversity be related through photosynthetic pathway differences that occur as a function of environmental conditions? Modeling efforts predict shifts in C3/C4 plant abundance in response to changes in atmospheric carbon dioxide. Our objectives are to better understand the constraints that atmospheric carbon dioxide places on ecosystem productivity, which may in turn influence mammalian grazers.