This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: New analyses of ancient cattle, sheep and goat bones on Madagascar suggest the rapid spread of introduced livestock on the island 1,200 years ago coincided with forest loss and population declines of large native herbivores. Madagascar provides a unique window into extinct ecosystems and the roles humans play in biodiversity loss, said study co-leader Sean Hixon, a postdoctoral researcher in associate professor Rebecca Terry's integrative biology lab at Oregon State University.
The findings, coupled with evidence that humans may have first appeared on Madagascar thousands of years before introduced livestock did, suggest hunting alone did not drive the extinction of giant lemurs and other megafauna. The study, published in Proceedings of the Royal Society B: Biological Sciences, adds to a treasure trove of scientific discoveries fueled by the nation 250 miles (400 kilometers) off the east coast of Africa. As many as 90% of the species that live on Madagascar, which is roughly the size of Oregon and California combined, are found nowhere else.
Its plants and animals evolved independently from those on other continental landmasses for about 88 million years. "Over the past five years, we brought together the largest collection to date of ancient, introduced livestock bone samples from across Madagascar for radiocarbon and stable isotope analysis," Hixon said. "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." Hixon said sedimentary pollen-based vegetation reconstructions indicate that grasses likely became more abundant across much of the island within the last millennium.
These reconstructions involve analyzing fossil and subfossil pollen grains preserved in sediments to infer past plant communities at regional scales and beyond. Meanwhile, paleoclimate reconstructions suggest that drying occurred at different times across the island during recent millennia. Drying was previously thought to be a key driver of past large-animal extinctions.
Over the past 1,000 years, Madagascar's cattle likely came to rely more on C4 grasses—grasses whose photosynthesis process is well suited to warm and dry weather, unlike the C3 grasses that thrive in cooler and damper 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 the island.
The study reinforces the pattern that, regardless of regional climate changes occurring at different times, endemic large herbivores disappeared around the time livestock and predators such as dogs were introduced. That suggests a causal 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," Hixon said.
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