Researchers Suggest New “Subsistence Shift Hypothesis” to Explain Megafaunal Extinction on Madagascar

megafauna
Malagasy graduate student and research team member Peterson Faina with stalagmites in a cave in Madagascar.

A new study suggests that a rapid population crash of megafauna on Madagascar between 700-1000 AD was triggered by a fundamental shift in the island population’s society and economy, as the introduction of slash-and-burn agriculture led to habitat destruction, an increase in human population and, ultimately, greater hunting pressure. The megafauna never recovered from this population crash, leading to their extinction.

This “Subsistence Shift Hypothesis,” as the inter-disciplinary team of researchers from the University of Massachusetts Amherst and colleagues from other universities call it, brings together the results from three years of research, along with new data on evidence of human butchery via cut-marks. The new chronology of human activity, megafaunal abundance and climatic changes finds that humans existed alongside and hunted the megafauna for millennia without a decline in megafauna population, and that the megafaunal decline occurred only after the introduction of slash-and-burn agriculture and the transition in the human economy from hunting and foraging to farming.

The findings, published in the May 2019 issue of Journal of Human Evolution, come from a team consisting of UMass Amherst’s Laurie R. Godfrey, Nick Scroxton, Stephen J. Burns, Michael R. Sutherland and Ventura R. Pérez, David McGee of the Massachusetts Institute of Technology, Brooke E. Crowley of the University of Cincinnati and Peterson Faina and Lovasoa Ranivoharimanana of Université d’Antananarivo Madagascar.

“The subsistence shift hypothesis is supported by the facts that the megafaunal crash was not coincident with initial human arrival, nor did it follow human arrival within a few centuries. It was not triggered by aridification,” the researchers write. “It did, however, begin at around the time cattle were introduced to Madagascar, and it peaked as human populations began to grow rapidly.”

The researchers revisited the question of Madagascar megafauna extinction by updating and comparing three sources of data: the radiocarbon record for subfossil vertebrates, which has improved significantly in the last 15 years; new data on human butchery of extinct lemurs during the past 2,000 years; and calcium carbonate cave deposits, or speleothems, such as stalagmites.

They posit that the varying rates of the disappearance of these animals across the island can be traced to habitat modification by humans, specifically forest cutting and burning caused by population growth and increased trade, combined with the continued pressure on the animals’ populations due to hunting.

“The expansion of Madagascar’s trade network, influx of new settlers, and economic transition from hunting and foraging to herding and farming triggered rapid growth in the size of the effective human breeding population, greater direct exploitation of wild (in addition to domesticated) animals, and more rapid habitat modification (a change in the fire ecology of the island),” they write. “Prior to this, small human populations appear to have continually or intermittently occupied Madagascar over an extended period of time without triggering extinction. Megafaunal extinction occurred only after the expansion of the Indian Ocean trade network, when forest clearance through cutting and burning would have served the economic needs of both herders and farmers, who would have also hunted wild animals to varying degrees.”

The team members from UMass Amherst were lead author of the study and emeritus professor of anthropology Godfrey, postdoctoral associate in geosciences Scroxton, professor of geosciences Burns, emeritus director of the Statistical Consulting Center Sutherland and associate professor of anthropology Pérez.

McGee is associate professor of earth, atmospheric and planetary studies at MIT. Crowley is associate professor of geosciences at Cincinnati.