National Museum of Natural History Smithsonian Institution Washington, D.C.
Paleoecology of the Smithsonian-Roosevelt African Expedition
Theodore Roosevelt famously led an expedition to East Africa to collect specimens of African mammals for the Smithsonian Institution following his retirement from the presidency in 1909. The 512 mammals he collected present a remarkable snapshot of ecology and environment in Kenya at the turn of the century. Using stable isotope analysis, we can learn important details about the ecology of these mammals and how modern life in East Africa - including habitat fragmentation, urbanization, industrialization and growing human-wildlife conflict - have changed their diets and behavior, and what conservation tactics we can employ to better protect them.
Reconstructing urban fossil fuel use
Understanding fossil fuel and point source emissions is cities is complicated by the fact that these kinds of measurements have not been historically made in many US cities. Using stable and radioisotopes of carbon in urban tree rings, we can determine the source of atmospheric carbon dioxide over the course the tree's growing history and reconstruct patterns of traffic density and urbanization in American cities.
Paleoclimate, paleoenvironments and human evolution
I am broadly interested in using stable isotopes in fossil tooth enamel in order to reconstruct paleoenvironments in East Africa at different periods of human biological and cultural evolution. Currently, I am using my research to assess how changes in local environment due to climate may have influenced the spread of herding or herders in East Africa, and what kinds of unique challenges may have been presented to Kenya's first herders due to changing environments. I am also interested in paleoenvironments and paleobiology of mammals in the Plio-Pleistocene, as well, with and emphasis on paleoecology during periods of high climatic variability, and issues of isotope signal attenuation and blurring in faunal assemblages during these time periods.
Holocene paleoenvironments in Kenya
Milankovitch periodicity (changes in the shape of the Earth's orbit) is one of the primary driving forces behind tropical climate variability. In equatorial Africa, eccentricity-mediated precession is particularly important in determining the timing and strength of the monsoon over geologic time. Although we see abundant evidence in the geologic record for wet-dry cycles that appear to be determined by precessional forcing, we do not currently have a good understanding of how these large-scale climatic changes translate to terrestrial ecology, especially on millennial timescales. My research involves stable isotope analysis of mammalian tooth enamel and sedimentary leaf wax biomarkers to reconstruct basinal scale ecology during the Holocene in two distinct basins in Kenya, the Turkana Basin and the Victoria Basin, in order to understand connections between climate and ecology across both time and space.
Stable Isotope ecology of modern East African environments
In order to gain a more accurate understanding of the past, we require on-going research on how isotopes are distributed in the modern environment. I have initiated projects on stable isotope ecology in national parks and protected areas in Uganda. This work includes analysis of modern mammalian teeth, soils and plants. In particular, collection and analysis of modern Ugandan plants for leaf wax biomarkers will refine our interpretations of biomarker isotope analysis in older sediments. I also work on isotope ecology of modern mammals in Kenya and Uganda. Ongoing modern isotope studies will create a more robust interpretive framework in addition to assisting wildlife authorities with management and conservation issues.