The Anthropocene era is marked by the impact of human activities on our environment, forcing a rethink of the complex ways that our societies interact with the Earth-system. What happens when humans move into a new place? How do the changes we make cause other, unforeseen changes? Now, a new paper in Proceedings of the Royal Society B examines the case of Madagascar, revealing how the introduction of domesticated livestock transformed the island.

The research team, led by Sean Hixon of the Max Planck Institute of Geoanthropology, uses radiocarbon dating of bovid remains to show that, after their introduction roughly 1,200 years ago, livestock spread rapidly throughout Madagascar. The researchers then analysed the stable isotopes preserved in cattle bone protein and found that the animals’ diet changed over time, reflecting a change in landscape and vegetation after their introduction.

“Our isotope analysis shows that cattle diet changed towards more reliance on C4 grasses – the grasses that typically grow in dry, open settings. At the same time, pollen records indicate that grasses in general were becoming more common across the island,” says Hixon. “Together, these signals suggest that there was vegetation clearance and the widespread use of land for grazing during the past millennium.”

The apparently rapid spread of livestock across Madagascar and the increasing reliance of cattle on C4 grasses suggests that pastoralism could have contributed to observed declines of forest-dwelling endemic animals. The timing of these shifts, potentially millennia after humans first arrived on the island, indicates that hunting alone did not drive the extinction of Madagascar’s giant lemurs and other megafauna.

“Our data show that, even if livestock do not directly drive forest loss and the spread of grasslands, the spread of livestock across the island is associated with forest fragmentation,” says Ricardo Fernandes, senior author from the MPI of Geoanthropology. “For primarily forest-dwelling animals such as the giant lemurs, these changes to the environment may have been too much to endure.”

This scenario, in which the pressures of human-driven changes to an ecosystem are combined with hunting, is unlike the “overkill” previously envisioned for North American megafuana. Instead, it reveals the complex relationships that, not only humans, but indeed all animals have with their environment.

Because livestock remain an important insurance against crop failure on Madagascar, the historical context given by the present findings highlights the importance of efforts to both boost suitable foraging space in existing open habitat and prevent encroachment on remaining forest.

Sean Hixon
hixon@gea.mpg.de

Dr. Ricardo Fernandes
fernandes@gea.mpg.de

Title: Past rapid spread of introduced livestock coincided with vegetation clearance on Madagascar

Authors: Sean Hixon, Leanne Phelps, Lucien Rakotozafy, Zoë Crossland, Mary E. Prendergast, Chantal Radimilahy, Henry T. Wright, Noel Amano, Nicole Boivin, Alison Crowther, Kristina Douglass, Andrius Garbaras, Richard George, Sophia Hüsges, Anneke Janzen, Douglas J. Kennett, Heritiana Randrianatoandro, Stefanie Schirmer, Axel Steinhof, Ricardo Fernandes

Publication: Proceedings of the Royal Society B

Researcher Lucien Rakotozafy sampling bone in collections housed in the capital, Antananarivo

Copyright: © Lucien Rakotozafy