Sunday, February 16, 2014

Tortoise poop

Thanks to Charles Darwin, the Galapagos Islands are known as a biological wonderland. After all, it was the relationships between its species which enabled Darwin to understand how different species could arise from a common ancestor.

But from a different perspective; the Galapagos actually aren’t species-rich; visitors to the islands often are surprised at how limited the number of species there really are compared to the mainland. The islands are remote, nearly 1000 kilometers from the mainland, and only a handful of species could ever make that trip.

In that setup…it turns out that the Galapagos tortoises wound up playing the role of a keystone species, one which the entire ecosystem depended on.

In new research, Dr. Cynthia Froyd of Swansea University took samples of soils throughout the Galapagos and tested them for the types of environments recorded and the species present.

They found that, prior to 500 years ago; they found “dung-affiliated” fungi, suggesting a large, plant-eating organism dominated the area. Since there aren’t other options living in the Galapagos wetlands, the only option was the tortoises.

Prior to the arrival of man, tortoises roamed freely across the islands, but starting in the 16th century, their numbers declined from 250,000 to 14,000 by 1970, and 5 of the original 14 subspecies have gone extinct.

At the same time, wetlands began drying up, a change recorded by the soil samples. About 500 years ago, the tortoise feces vanish, and at the same time, the plants change. The freshwater wetlands that once populated large areas of the Galapagos dried and the plants supported by those wetlands began dying, disappearing, and even going extinct.

The plants which supported those wetlands relied on the tortoises in several ways, including fertilization and churning up the ground as they walked through. The tortoises were a keystone species; once they began dying, the entire ecosystem surrounding them died with them.

Today, efforts are underway to protect the remaining tortoises and to introduce them into their previous environments, but many of the areas where the tortoises used to live simply don’t exist anymore. Once the tortoises died or were killed, the wetlands died with them, and reestablishing the entire ecosystem will be a difficult, long-term task.

Image credit: Wikimedia commons

Original paper:

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