Galapagos tortoises, which live in the South Pacific, are starting to eat invasive plants that could benefit their health, according to a new study. This nonnative vegetation appears to be providing a nutritional boost to the endangered animals, research reveals.
The island of Santa Cruz in the Galapagos is an extinct volcano heavily populated by human beings. People there have farmed much of the rich soil, covering large portions of the island with farm crops nonnative to the area.
During an earlier study, researchers fitted GPS devices to tortoises on Santa Cruz, finding that the animals regularly moved between highland meadows that offered food year-round and lowlands, where food only grows during the wet season. Only 14 percent of the highland regions are still populated largely by native species of plants.
This behavior from the tortoises seemed unusual because the animals can go a year between meals. Researchers wondered why the 500-pound creatures would expend energy on moving between the two regions when they could simply wait out the dry season.
Researchers studied the animals for four years, watching their movements and examining their dung for the presence of seeds to precisely measure food intake. A veterinarian regularly weighed the animals and took blood samples as part of the study.
Galapagos tortoises were found to spend more time eating crops bred by humans than those native to their habitat.
"We weren't really that surprised. Consider it from a tortoise's point of view. The native guava, for example, produces small fruits containing large seeds and a small amount of relatively bitter pulp in a thick skin. The introduced guava is large and contains abundant sweet pulp in a thin, pliable skin," Stephen Blake from Washington University in St. Louis said.
The nonnative plants seem to be providing roughly half of the nutrition for the turtles, offering the animals a boost in their health and energy. These crops were first introduced en masse to the island group in the 1930s as agriculture began to dominate the region.
Galapagos tortoises were once prevalent around the globe, appearing on every continent except Antarctica. Today, the animals are only seen in two locations — the Galapagos Archipelago and the Aldabra Atoll in the Indian Ocean. Every subspecies of the tortoise that still exist in the Galapagos is currently classified as endangered or vulnerable.
Invasive species are usually harmful to environments to which they are introduced. However, all indications suggest that tortoises in the Galapagos are benefiting from eating crops bred for human agriculture.
Analysis of feeding habits of Galapagos tortoises was detailed in the journal Biotropica.
Photo: Eric Chan | Flickr
