Doctoral Dissertation Improvement Award: Aridification and Environmental Change

The intrinsic and economic values of biodiversity make species extinction a significant societal concern. To conserve the existing variety of species, it is important to understand past and present drivers of biodiversity loss. Archaeology and paleoecology provide relevant, long term perspectives on interactions among humans, other organisms, and climate that contribute to extinctions. This project will answer several longstanding questions regarding how a drying climate and the early colonization of Madagascar by humans and associated introduced species may have contributed to past extinctions of large animals on the island. For example, to what extent did humans hunt the now extinct animals? Did introduced animals compete with now-extinct natives, and were introduced animals drought-tolerant relative to natives? Recognizing feedbacks among sources of regional change is a challenge, but this case study of datasets from Madagascar is broadly applicable to the study of past interactions among organisms in the face of aridification. Given the relevance of this research to present environmental concerns and the ongoing development of drought-related policy in arid southwest Madagascar, community and local government outreach is a project priority. This interdisciplinary work involves students and faculty at Malagasy universities, and the students trained through the field component of this research will gain skills applicable to data gathering and natural resource management. This research investigates some of the many ways in which the arrival of humans and introduced species in a novel environment may have contributed to past and ongoing biodiversity loss. The field component of this project focuses on the coast of southwest Madagascar. This region is ideal for studies of environmental changes associated with human activity, because humans and human-introduced animals (e.g. goats, pigs, cattle, dogs, cats, and rats) arrived on the island several thousand years ago, and the bones of extinct endemic animals (e.g. pygmy hippos, giant tortoises, elephant birds, and giant lemurs) are abundant along this coastline. Survey and excavation of a series of coastal ponds with traces of past human presence serve to recover the material record of past human activity and biodiversity loss. Radiocarbon dating of bone recovered from fieldwork and museum collections provides the chronological control that is necessary to infer past interactions among humans, other organisms, and environmental change. A series of chemical analyses of radiocarbon-dated bone protein is used to trace aspects of organisms' diets and environments through time. These analyses, coupled with a separately-funded effort to reconstruct the past climate of the region through the chemical analysis of ancient lake sediments, make it possible to examine potential synergies between past human activity and the changing climate that may have driven past extinctions on the island. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.