On Ancient Madagascar, Large Native Herbivores Paid the Price as Introduced Livestock Spread

Adapted from an Oregon State University press release written by Steve Lundeberg.

New analyses of ancient cattle, sheep and goat bones on Madagascar suggest that the rapid spread of introduced livestock on the island 1,200 years ago coincided with forest loss and population declines among large native herbivores.

A research team led by Oregon State University and the Columbia Climate School published their results in the journal Proceedings of the Royal Society B.

Madagascar provides a unique window into extinct ecosystems and the role humans play in biodiversity loss, said the study’s co-lead author Sean Hixon, a postdoctoral researcher at the Oregon State University College of Science. As many as 90% of Madagascar’s species are found nowhere else. Roughly the size of Oregon and California combined, the island nation has been home to plants and animals that evolved largely in isolation for about 88 million years.

The findings, coupled with evidence that humans may have arrived on Madagascar thousands of years before introduced livestock became widespread, suggest that hunting alone did not drive the extinction of giant lemurs and other megafauna. Instead, the study points to a more complex period of ecological change involving introduced animals, vegetation shifts, climate variability and changing human land use.

“Madagascar’s past shows how tightly linked livelihoods, climate, vegetation and biodiversity can be,” said study co-lead author Leanne Phelps, an associate research scientist working in the Olo Be Taloha Lab based at the Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School.

Over the past five years, the researchers brought together the largest collection to date of ancient introduced livestock bone samples from across Madagascar for radiocarbon and stable isotope analysis.

“The data confirm that livestock rapidly spread across the island about 1,200 years ago, approximately coinciding with the disappearance of animals like elephant birds and pygmy hippos,” said Hixon.

Sedimentary pollen-based vegetation reconstructions indicate grasses likely became more abundant across much of Madagascar within the last millennium. These reconstructions involve analyzing fossil and sub-fossil pollen grains preserved in sediments to infer past plant communities at regional scales and beyond.

Meanwhile, paleoclimate reconstructions suggest that Madagascar experienced uneven patterns of drying during recent millennia, complicating earlier ideas that climate change alone was a key driver of past large animal extinctions.

Over the past 1,000 years, Madagascar’s cattle likely came to rely more heavily on C4 grasses—grasses whose photosynthesis process is well suited to warm and dry weather—as opposed to C3 grasses, which thrive in cooler, wetter conditions.

“Although cattle might have preferred wet habitat, they successfully exploited relatively dry habitat during their earlier spread across the island,” Hixon said.

He added that the earliest documented presence of sheep and cattle in the island’s interior more than a millennium ago likely reflects a rapid spread of livestock across Madagascar. The study findings reinforce the pattern that, despite regional climate changes that unfolded at different times across the island, endemic large herbivores disappeared around the time livestock and predators such as dogs were introduced. This suggests a link between livestock proliferation and past extinctions.

The comparatively late arrival of livestock and the megafauna extinctions, coupled with the early human arrival estimate, suggests that it wasn’t just hunting by humans that drove the extinctions.

“The next step is to understand more about the causal relationships between these associated human and environmental changes, how their relationships varied across Madagascar’s diverse landscapes, and the practical relevance of that for supporting healthy livelihoods and biodiversity today,” Phelps said.

Because livestock on Madagascar remain an important component of many livelihoods, Phelps added, the historical context highlights the immediate importance of efforts to both boost suitable forage in existing open habitat and prevent degradation in remaining biodiverse ecosystems.

“This livestock database can contribute to improving understanding of complex interactions among livestock, people, biodiversity and diverse environmental factors on Madagascar,” she said. “This is essential not only for understanding environmental change in the past, but also for informing land stewardship today and in the future.”

Max Planck Society and the National Science Foundation supported this research. The study featured an international collaboration of scientists from 19 institutions, including Princeton University, Rice University, the University of Michigan, Pennsylvania State University and the University of Tennessee.