In 2012, the world mourned the loss of Lonesome George, a 100-year-old giant tortoise that resided on the Galapagos Island of Pinta. While losing any member of these ancient species that outlive most humans is sad, what made it worse was that George was believed to be the last known living member of the Pinta Island giant tortoise subspecies. Fortunately, the same fate does not await the Hood Island giant tortoises of Española Island.
According to a new study published in the scientific journal PLOS ONE on October 28th by James Gibbs, a biology professor at the State University of New York College of Environmental Science and Forestry, the island is now home to over 1,500 of the giants. This is a far cry from just fifty years ago, when the population of the saddle-backed shell tortoises that once used to inhabit Española Island in the thousands, had been reduced to just 14 - a number that included 12 females and two males.
The decimation of the species was attributed to two factors. During the 18th and 19th centuries the tortoises were captured in large numbers by buccaneers, whalers and other sea-goers passing through the Galapagos Islands. According to Linda Cayot, the science advisor to the Galapagos Conservancy Group, the ancient reptile's popularity stemmed from the fact that they are able to survive without food or water for an entire year. This meant that they could be taken live on long voyages and used as a natural source of fresh meat.
The other and probably bigger contributor to their demise was the introduction of goats to the remote island by fishermen seeking a supply of meat for return voyages. The animals grazed through everything they could lay their eyes on, including the cacti that helped sustain the tortoises during the dry season.
With not much to feed on, the animals stopped moving around the low rocky island that measures just 60 square km. That made things worse because as the tortoises walk around, they disseminate cacti seeds through their droppings. This helps spur the growth of the succulent plants, which also provide sustenance for finches and mockingbirds, as well as reptiles like lava lizards. Hence, as the population of the giant tortoises declined, so did the island's biodiversity.
When the island was finally declared a nature reserve in 1959, most conservationists thought that the Española giant tortoises were extinct. Fortunately, they were able to find the last 14 that were still roaming around. These along with a male tortoise that was living at the San Diego Zoo in California, were brought together by naturalists at the Galapagos National Program for a captivity breeding experiment. Given that previous attempts with other giant tortoise species had failed, nobody knew what to expect. However, slowly but surely, the experts were able to revive the population to a number that Gibbs believes is large enough to allow the tortoises to sustain themselves, alleviating the need for additional human aid.
But the researcher warns that things are not quite back to normal. That's because though the goats were eradicated in the early 1970's, the grass and cacti that once dotted the tiny island has been replaced by woody plants. Though he is confident that the giant tortoises will be able to trample the plants, respread the cacti and restore the island back to its formal glory, he warns that the process could take a few centuries.
Native to seven of the several volcanic islands that make up Ecuador's Galapagos Island arch, the Galapagos giant tortoise is the largest living species of its kind and the 10th heaviest living reptile in the world. While all of them are huge, the size and shape of the tortoises vary, depending on the island they reside on.
Those that live in the humid regions are generally larger and feature domed shells and shorter necks. The species endemic to the drier areas like Española, are smaller, have saddle-shaped shells and longer necks. In fact, the Hood Island specimens are the smallest of the giant tortoise subspecies. Scientists believe that it may have to do with the size of the tiny island they inhabit. The tortoises have also evolved longer limbs, extended necks and arched carapace openings that allow them to get to vegetation that is out of reach for most of the other subspecies. What's interesting is that it was the differences in each of the subspecies of these ancient reptiles that inspired Charles Darwin's 1859 theory of evolution by natural selection.
Resources: newsweek.com,takepart.com,news.yahoo.com, webecoist