With support from the Packard Foundation, we are exploring the relationships between photosynthetic pathway, changing atmospheric CO2, and mammalian herbivores. Atmospheric CO2 levels have changed over the last 200 million years; the recent pattern of increasing anthropogenic emissions has resulted in a dramatic increase in atmospheric CO2 today that differs from atmospheric CO2 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 CO2 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 abundance in response to changes in atmospheric CO2. The objectives of Packard C3/C4 interdisciplinary research are to better understand the constraints that atmospheric CO2 places on ecosystem productivity, which may in turn influence mammalian grazers.