Are invasive species good for giant tortoises? Ask the dung

From the Congo to the Galapagos Islands, Stephen Blake has dedicated his career to protecting endangered animals.  He says that in most cases, invasive species spell trouble for native species, especially if they are endangered.  “While introduced species, in general, are generally a bad thing for Galapagos ecosystems and any ecosystem, there are bits to that story, there are nuggets to that story that make it a little bit more complicated.”  That complication comes in the form of giant Galapagos Tortoises. For them, non-native grass and fruit species appear to be putting a spring in their step.

Blake and his colleagues observed that the tortoises, some weighing more than 500 pounds, will travel out of their way to where invasive species thrive for some lunch.  Apart from watching massive animals eat, Blake needed to quantify exactly how much and which invasive species the tortoises were munching on. He did that by “Analyzing tortoises dung piles and so my colleague Freddy Cabrerra have, and I think we have been through 300 to 400 hundred dung piles by this point counting every single seed in a pile of dung and sometimes you get 7 or 8 thousand seeds in a single dung pile, so it’s been a lot of work.”

And, according to Blake, it’s important work. He says that while the tortoises appear to be thriving on the invasive species, the long-term effects are still unknown.  “One could imagine tortoises modifying potentially their migration and movement behavior through special memory and things like that. Suddenly there is a nice new patch of nutritious stuff here that didn’t exist ten years ago so I will come back here next year.”

That change could affect migratory routines that could, in turn, affect reproductive patterns. But to answer those questions, Blake says only time….and a lot more dung…will tell.

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