The Galapagos Islands, a remote set of islands located far off the coast of Ecuador, are best known for their influence on Charles Darwin’s theory of evolution – because the plants and animals found there aren’t found anywhere else, he could study them in a controlled, contained environment. However, as with all things humans touch, our interference has changed the Islands in the form of alien, invasive plant species. Now, a new study reveals that nature has a peculiar justification for their spread: The endangered giant tortoise.
Researchers Stephen Blake, PhD, an honorary research scientist at Washington University in St. Louis, and Fredy Cabrera, of the Charles Darwin Foundation in the Galapagos, found that not only do the giant tortoises seem to prefer some of the invasive plant species, but they seem to thrive on them.
Blake and Cabrera happened upon the finding while researching a different phenomena: Galapagos tortoises appeared to be able to go as long as a year without food or water, and yet the researchers observed them migrating between lowlands and highland meadows. Why, they wondered, would a creature capable of fasting until the next rainy season lug a heavy shell up and down a rocky mountain? In fact, they even wondered where they got the energy to do so.
By closely watching what they ate and identifying plant specimens in the tortoises’ dung, they found that the tortoises spent a lot of time foraging among non-native invasive plant species, to the point where they made up nearly half their diets.
“Consider it from a tortoise’s point of view,” Blake told Discovery News. “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.”
What’s more, a physical examination of the tortoises found that the invasive plants at worst had no effect, and may even significantly improve the tortoises’ health. It makes sense – an animal with access to ample calories and nutrients will be healthier than one without, which explains why the tortoises are willing to make the journey to the highland meadows, which produce vegetation year round.
Though the tortoises aren’t nearly numerous enough to have any meaningful impact on the spread of invasive plant species, Blake says it’s nice to find a silver lining, of sorts.
“Eradicating the more than 750 species of invasive plants is all but impossible, and even control is difficult. Fortunately, tortoise conservation seems to be compatible with the presence of some introduced species,” he said.