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Giant Tortoises Crawl Back From Extinction’s Edge In Galapagos

<p><a class="checked-link" href="http://www.eurekalert.org/multimedia/emb/81557.php?from=280615" style="text-decoration: none;">Credit: James P. Gibbs, SUNY-ESF</a></p>

The population of giant tortoises on Española, an island in the Galapagos archipelago, has increased almost seventy-fold over the last half century. In the ‘60s, a captive breeding program reintroduced 15 of the titan tortoises - they can weigh up to 600 pounds - to the island. Today, there are about 1,000 of the reptiles.

"It's a rare example of how biologists and managers can collaborate to recover a species from the brink of extinction," says biologist James P. Gibbs, in a statement. Gibbs, a researcher at the State University of New York, and his colleagues from the U.S. and Ecuador recently reviewed the ecological and demographic results of this recovery in the journal PLOS ONE.

For decades, feral goats roamed the island. Until they were removed in 1978, the goats may have fostered the spread of different types of plants; over that time, the wilds of Española changed from tastier (to reptiles) plants like prickly pear cactuses into more woody, less tortoise-friendly vegetation. Although the population of tortoises now seems stable - with a very low calculated risk of extinction - it won't continue to climb until the cactuses reclaim more of their historic range.

A tortoise takes a breather underneath a prickly pear cactus, with woody shrubs in the background. (Credit: Gibbs et al.)

Promoting more cactuses would be a boon to other species as well, Gibbs and his colleagues note. Lots of woody shrubs act as a barrier, for example, to the endangered waved albatross. Albatrosses are awkward birds, and, like commuter jets, they need plenty of flat, clear space to achieve liftoff.

Tortoises act as so-called "ecosystem engineers," restructuring plants through foraging and, on the other end, seed dispersal. But they need human help, the scientists write, to further restore the beneficial plants in Española.