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Transplanted giant tortoises revive ecosystem in Mauritius

Saturday, May 07, 2011 by: M.Thornley
Tags: tortoises, ecosystem, health news

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(NewsTarget) Ile aux Aigrettes, an island off the coast of Mauritius, was once a species haven. Giant tortoises weighing up to six hundred pounds helped propagate the island`s ebony trees by eating its fruit and dispersing the seeds. But once this delicate ecosystem was disturbed by humans cutting down the trees for firewood, and killing the turtles, birds and lizards, the island`s trees could no longer spread. The fruit formerly eaten by tortoises and lizards dropped to the ground under the trees and grew there only. In an attempt to restore the lost ecosystem, researchers introduced another species of giant tortoise.

Whaling ships and buccaneers in the 18th and 19th centuries used tortoises for food. Logbooks kept by these adventurers record harvests that number 250,000 and more. Their fat was also burned in oil lamps to provide light.

Although replacing an extinct life form with another is controversial, it has been done. Examples are the North American peregrine falcon and yellow crowned night herons in Bermuda. The falcon was re-established using seven subspecies from different locations. Yellow crowned night herons were brought to Bermuda in the hope that they would succeed in replacing the former herons that ate nuisance land crabs.

The tortoise selected for this project was the Aldabra. Aldabra tortoises are second to the Galapagos tortoise in size. An Aldabra can weigh more than 500 pounds and live to be ninety or more. They are vegetarian, eating grasses and herbs. They can reach as high as three feet to browse on plants.

The Aldabra tortoise once populated Madagascar and the Seychelles Islands. But in the 1900s the species was decimated to the point of extinction due to hunting. The Seychelles government intervened to stop the slaughter. Currently, about 100,000 Aldabra tortoises exist in the wild.

Because islands tend to have few predators, re-establishing giant tortoises is simpler than replacing falcons in America or herons in Bermuda. Also, the island, Ile aux Aigrettes, was uninhabited.

However, researchers were cautious about introducing the new tortoises. They feared the tortoises might eat too many native plants.

In 2000 four tortoises were delivered to the island, followed by others. In 2005, eleven were released from the pens where they had been kept for initial observation.

Changes wrought by the tortoises so far seem to indicate success. Ripe fruit that used to be found lying under the ebony trees are now in scant supply. In areas frequented by the tortoises, tree seedlings are beginning to appear. Researchers determined that seeds germinated better after passing through a tortoise gut. Trees and tortoises were truly a synergetic relationship.

And that isn`t all. The tortoises proved also to be levelers of non-native plants.

It remains to be seen if the ebony seeds the new giant tortoises were instrumental in distributing become reproductive adult trees. But researchers are sufficiently encouraged by the results to begin to consider using tortoises to rehabilitate other islands.


About the author

M. Thornley enjoys walking, writing and pursuing a raw vegan diet and lifestyle.

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