More detail below. Thanks for posting, OP!
"In the late 19th century, whalers, settlers, and pirates changed the ecology of the Galapagos Islands by poaching some native species—like Galapagos giant tortoises—and introducing others, like goats and rats. The latter species became pests and severely destabilized the island ecosystems. Goats overgrazed the fruits and plants the tortoises ate while rats preyed on their eggs. Over time, the tortoise population plummeted. On Española, an island in the southeast of the archipelago, the tortoise count fell from over 10,000 to just 14. Along the way, with goats eating all the plants they could, Española—once akin to a savanna—turned barren.
A century later, conservationists set out to restore the Galapagos giant tortoise on Española—and the island ecosystem. They began eradicating the introduced species and capturing Española’s remaining tortoises and breeding them in captivity. With the goats wiped out and the tortoises in cages, the ecosystem transformed once again. This time, the overgrazed terrain became overgrown with densely packed trees and woody bushes. Española’s full recovery to its savanna-like state would have to wait for the tortoises’ return.
From the time those 14 tortoises were taken into captivity between 1963 and 1974 until they were finally released in 2020, conservationists with the NGO Galápagos Conservancy and the Galapagos National Park Directorate reintroduced nearly 2,000 captive-bred Galapagos giant tortoises to Española. Since then, the tortoises have continued to breed in the wild, causing the population to blossom to an estimated 3,000. They’ve also seen the ecology of Española transform once more as the tortoises are reducing the extent of woody plants, expanding the grasslands, and spreading the seeds of a key species.
Not only that, but the tortoises’ return has also helped the critically endangered waved albatross—a species that breeds exclusively on Española. During the island’s woody era, Maud Quinzin, a conservation geneticist who has previously worked with Galapagos tortoises, says that people had to repeatedly clear the areas the seabirds use as runways to take off and land. Now, if the landing strips are getting overgrown, they’ll move tortoises into the area to take care of it for them.
The secret to this success is that—much like beavers, brown bears, and elephants—giant tortoises are ecological architects. As they browse, poop, and plod about, they alter the landscape. They trample young trees and bushes before they can grow big enough to block the albatrosses’ way. The giant tortoises likewise have a potent impact on the giant species of prickly pear cactuses that call Española home—one of the tortoises’ favorite foods and an essential resource for the island’s other inhabitants.
When the tortoises graze the cactus’s fallen leaves, they prevent the paddle-shaped pads from taking root and competing with their parents. And, after they eat the cactus’s fruit, they drop the seeds across the island in balls of dung that offer a protective shell of fertilizer...
As few as one or two tortoises per hectare [about 2.5 acres], the scientists write, is enough to trigger a shift in the landscape."
-via Popular Science, October 15, 2023
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