Almost all megafauna of Madagascar – including the famous dodo bird, lemurs the size of a gorilla, giant tortoises and the elephant bird that was 10 feet tall and weighed about half a ton – disappeared between 1500 and 500 years ago. Were these animals overhunted to extinction by humans? Or did they disappear because of climate change?
There are numerous hypotheses, but the exact cause of this megafauna disappearance remains elusive and highly debated. The Mascarene Islands east of Madagascar are of special interest because they are among the last islands on Earth to be colonized by humans. Interestingly, the megafauna of the islands precipitated in just a couple of centuries after human settlement.
In a recent study published by the journal Science Advances, a team of international researchers found that what doomed the megafauna was indeed likely a “double whammy”, starring an intensification of human activities in combination with a particularly severe period of aridity throughout the region. The researchers rule out that climate change is the sole cause, and instead suggest that the impact of human colonization was a crucial contributor to the collapse of the megafauna.
Hanying Li, from Xi’an Jiaotong University in China and lead author of this study, compiled a detailed history of regional climate variations. The main source of this new paleoclimatic record came from the small Mascarean island of Rodrigues, in the southwestern Indian Ocean, approximately 1600 km east of Madagascar. “An island so remote and small that it is not found in most schoolbook atlases,” says Gayatri Kathayat, one of the co-authors and adjunct professor of climate science at Xi’an Jiaotong University.
By analyzing the stalagmites in the cave of La Vierge, located in Rodrigues, the scientists reconstructed 8000 years of the region’s past climate. (Photo: Hanying Li)
Li and his colleagues built their climate records by analyzing the trace elements and isotopes of carbon and oxygen in each layer of incremental growth of stalagmites that they collected from one of the many caves on this island. Most of these analyzes were carried out in the Quaternary Research Group of the Institute of Geology at the University of Innsbruck, led by Prof. Christoph Spötl: “Variations in geochemical signatures provided the information necessary to reconstruct the patterns precipitation in the region over the last 8000 years. To analyze the stalagmites we used the stable isotope method in our laboratory in Innsbruck. “
Despite the distance between the two islands, summer rainfall in Rodrigues and Madagascar is influenced by the same tropical rain belt around the world that oscillates from north to south with the seasons. “And when this belt falters and remains further north of Rodrigues, droughts can hit the entire region from Madagascar to Rodrigues, “explains Hai Cheng, the lead co-author of the study. “The work of Li de Rodrigues shows that the hydroclimate of the region experienced a series of drought trends over the last 8 millennia, which were frequently interrupted by ‘mega-droughts’ that lasted decades,” says Hubert Vonhof, scientist from the Max Planck Institute of Chemistry in Mainz, Germany, and co-author.
The most recent of the drought trends in the region began around 1,500 years ago, at a time when archaeological records began to show definite signs of an increased human presence on the island. “Although we cannot say with 100% certainty whether human activity, such as overhunting or habitat destruction, was the proverbial last straw, our paleoclimatic records clearly show that the megafauna had survived all previous episodes. of even greater aridity. This resistance to the climatic oscillations of the past suggests that an additional stressor contributed to the elimination of the megafauna of the region, “says Ashish Sinha, professor of earth sciences at California State University, Domínguez Hills. (United States).
“There are still many pieces missing to fully solve the puzzle of megafauna collapse. This study now provides an important multi-millennial climatic context for megafauna extinction,” says Ny Rivao Voarintsoa of the University of Leuven (Belgium), a native of Madagascar , who participated in this research. The study sheds new light on the shrinking flora and fauna of Mauritius and Rodrigues: “Both islands were rapidly stripped of endemic species of vertebrates in the two centuries following initial human colonization, including the well-known flightless ‘Dodo’ bird. from Mauritius and the Rodrigues’ endemic Rodrigues giant tortoise, “adds Aurele Anquetil André, administrator and principal curator of the François Leguat Reserve of Giant Tortoises and Rodrigues Caves.
“The story our data tells is one of resilience and adaptability of the islands’ ecosystems and fauna in past episodes of severe climatic oscillations over eons, until they were hit by human activities and climate change,” the researchers conclude. (Source: NCYT Amazings)